RTO-TR-059

AC/323(SET-005)TP/22
NORTH ATLANTIC TREATY ORGANISATION
RTO-TR-059

RESEARCH AND TECHNOLOGY ORGANISATION

BP 25, 7 RUE ANCELLE, F-92201 NEUILLY-SUR-SEINE CEDEX, FRANCE

© RTO/NATO 2002
Single copies of this publication or of a part of it may be made for individual use only. The approval
of the RTA Information Management and Systems Branch is required for more than one copy to be
made or an extract included in another publication. Requests to do so should be sent to the address
above.
RTO TECHNICAL REPORT 59

Electromagnetic Compatibility in the

Defense Systems of Future Years
(La compatibilité électromagnétique des systèmes de
défense de l’avenir)

Report of the RTO Sensors and Electronics Technology Panel (SET) Working Group WG-01.

Published June 2002

Distribution and Availability on Back Cover

This page has been deliberately left blank

Page intentionnellement blanche

 RTO-TR-059
AC/323(SET-005)TP/22
NORTH ATLANTIC TREATY ORGANISATION

RESEARCH AND TECHNOLOGY ORGANISATION

BP 25, 7 RUE ANCELLE, F-92201 NEUILLY-SUR-SEINE CEDEX, FRANCE

RTO TECHNICAL REPORT 59

Electromagnetic Compatibility in the Defense

Systems of Future Years
(La compatibilité électromagnétique des systèmes de défense de l’avenir)

Report of the RTO Sensors and Electronics Technology Panel (SET) Working Group WG-01.
 The Research and Technology
Organisation (RTO) of NATO
RTO is the single focus in NATO for Defence Research and Technology activities. Its mission is to conduct and promote
cooperative research and information exchange. The objective is to support the development and effective use of national
defence research and technology and to meet the military needs of the Alliance, to maintain a technological lead, and to
provide advice to NATO and national decision makers. The RTO performs its mission with the support of an extensive
network of national experts. It also ensures effective coordination with other NATO bodies involved in R&T activities.
RTO reports both to the Military Committee of NATO and to the Conference of National Armament Directors. It comprises a
Research and Technology Board (RTB) as the highest level of national representation and the Research and Technology
Agency (RTA), a dedicated staff with its headquarters in Neuilly, near Paris, France. In order to facilitate contacts with the
military users and other NATO activities, a small part of the RTA staff is located in NATO Headquarters in Brussels. The
Brussels staff also coordinates RTO’s cooperation with nations in Middle and Eastern Europe, to which RTO attaches
particular importance especially as working together in the field of research is one of the more promising areas of initial
cooperation.
The total spectrum of R&T activities is covered by the following 7 bodies:
• AVT Applied Vehicle Technology Panel
• HFM Human Factors and Medicine Panel
• IST Information Systems Technology Panel
• NMSG NATO Modelling and Simulation Group
• SAS Studies, Analysis and Simulation Panel
• SCI Systems Concepts and Integration Panel
• SET Sensors and Electronics Technology Panel
These bodies are made up of national representatives as well as generally recognised ‘world class’ scientists. They also
provide a communication link to military users and other NATO bodies. RTO’s scientific and technological work is carried
out by Technical Teams, created for specific activities and with a specific duration. Such Technical Teams can organise
workshops, symposia, field trials, lecture series and training courses. An important function of these Technical Teams is to
ensure the continuity of the expert networks.
RTO builds upon earlier cooperation in defence research and technology as set-up under the Advisory Group for Aerospace
Research and Development (AGARD) and the Defence Research Group (DRG). AGARD and the DRG share common roots
in that they were both established at the initiative of Dr Theodore von Kármán, a leading aerospace scientist, who early on
recognised the importance of scientific support for the Allied Armed Forces. RTO is capitalising on these common roots in
order to provide the Alliance and the NATO nations with a strong scientific and technological basis that will guarantee a
solid base for the future.

The content of this publication has been reproduced

directly from material supplied by RTO or the authors.

Published June 2002

Copyright  RTO/NATO 2002

All Rights Reserved

ISBN 92-837-1084-3

Printed by St. Joseph Print Group Inc.

(A St. Joseph Corporation Company)
1165 Kenaston Street, Ottawa, Ontario, Canada K1G 6S1

ii
 Electromagnetic Compatibility in the
Defense Systems of Future Years
(RTO TR-059 / SET-005)

Executive Summary
The recent increasing recognition of EMC problems is based on two facts (detailed below), calling for
an activity of assessment of the state of the art and a forecast of future trends.
The first fact is the increasing number of electronic equipment in every system, and the miniaturization
of the devices that can be achieved by the new technologies. The consequence is the requirement for
higher and higher frequencies and the increased likelihood of interference. The impact on the design at
system level is evident: better tools are needed to estimate the system performance and to specify the
EMC constraints, considering that conventional rules of thumb are inadequate to describe systems
which are electromagnetically complex.
The second fact of concern about EMC in the military environment is related to the coexistence and
harmonization between commercial and military standards. In fact, military standards are mainly
concerned with the immunity of equipment and their operation in the same installation (e.g., aircraft,
fixed station, etc.), with less concern for the ‘external world’. Commercial standards, on the contrary,
seek a ‘pacific’ coexistence of all equipment (i.e., reduced emissions and sufficient immunity).
Airborne platforms are foreseen to increase the number of on-board transmitters for satellite and
ground communications, self defense, monitoring and surveillance systems. The introduction of new
technologies, relying largely on miniaturization and high speed, is triggered by the reduced weight of
the equipment and the increased bandwidth of information processing.
Procurement Agencies may experience difficulties specifying the EMC requirements of next
generation systems, because new technologies involve physical phenomena and frequency ranges of
little concern in the past. The ability to produce correct specifications must rely on the updated
knowledge of the state of the art in technology, and has a great economical impact, since reduce the
risk for over/under specified systems which prove to be costlier.
The study has focussed on three areas of EMC design, development and qualification in future defence
systems. The limitations of existing techniques and standards have been examined and highlighted.
Such limitations cause risks at the present time. However, the risks will increase as a result of changes
in the commercial and technological environment. Potential increases in risk, as a result of these
changes in the absence of research development, have been highlighted. Furthermore,
recommendations on investment in research and development have been made in order to mitigate the
increasing risks.

iii
 La compatibilité électromagnétique
des systèmes de défense de l’avenir
(RTO TR-059 / SET-005)

Synthèse
La reconnaissance croissante actuelle des problèmes de CEM a pour origine deux états de fait (explicités ci-
dessous) qui appellent une activité de définition de l’état actuel des connaissances dans ce domaine, ainsi
que la prévision des tendances futures.
Le premier fait constaté est le nombre croissant de composants électroniques intégrés dans chaque système,
ainsi que la miniaturisation des dispositifs désormais permise par les nouvelles technologies. Il en résulte
une demande de fréquences de plus en plus hautes, associée à la probabilité accrue d’interférences.
L’impact sur la conception au niveau systèmes est évident : de meilleurs outils sont demandés pour évaluer
les performances des systèmes et pour spécifier les contraintes CEM, étant donné que les règles empiriques
traditionnelles ne suffisent plus à décrire des systèmes électromagnétiques complexes.
Le deuxième élément de préoccupation dans le domaine de la CEM militaire concerne le degré de
coexistence et d’harmonisation entre les normes militaires et les normes commerciales. En effet, les normes
militaires portent principalement sur l’immunité des équipements et leur fonctionnement au sein d’une
même installation (par exemple, aéronef, station fixe etc..), et concernent moins le “monde extérieur”.
Les normes du commerce, visent au contraire la coexistence “pacifique” de l’ensemble des équipements
(c’est-à-dire la réduction des émissions et une immunité suffisante).
Le nombre d’émetteurs aéroportés destinés aux communications terrestres et par satellite, à l’autodéfense,
et aux systèmes de contrôle et de surveillance doit normalement augmenter. La mise en application de ces
nouvelles technologies, qui privilégient la miniaturisation et la vitesse, s’explique par la masse réduite des
équipements et par l’augmentation de la bande passante utilisée pour le traitement de l’information.
Les agences d’achat pourraient rencontrer des difficultés lors de la spécification des besoins CEM de la
prochaine génération de systèmes, parce que les nouvelles technologies entraı̂nent des bandes passantes et
des phénomènes physiques peu connus jusqu’ici. La capacité d’établir des spécifications correctes passe par
des connaissances actualisées des technologies de pointe, et produit un impact économique considérable,
car elle permet de réduire le risque de fabrication de systèmes inadéquats et par conséquent, plus coûteux.
L’étude a privilégié les trois aspects de la conception, du développement et de la qualification des futurs
systèmes de défense. Les limites des techniques et des normes existantes ont été examinées et mises en
évidence. Aujourd’hui, de telles limites ont pour effet de créer des risques. Mais de tels risques seront plus
nombreux à l’avenir en raison de l’évolution de l’environnement commercial et technologique. Les risques
possibles, qui résulteraient de ces changements, en l’absence d’activités de recherche, ont été soulignés. En
outre, des recommandations ont été faites concernant l’investissement en recherche et développement qui
serait à faire afin d’atténuer les effets de ces risques accrus.

iv
 Click inside the blue boxes to view the corresponding section

Contents

Page
Executive Summary iii
Synthèse iv
The Working Group WG01 vi

1. Introduction and Motivation 1

2. Examination of the Limitations of Modelling and Testing 3
2.1 Description of a Generic Processes 3
2.2 Numerical modelling and present limitations 5
2.3 Test Techniques and Present Limitations 41
3. Applicable Standards for Military Systems 55
4. Evaluation of Standards and Proposals for Improvement 79
5. Risks in EMC of Future Systems 87
5.1 Risk Analysis 87
5.2 Specific considerations for safety related systems 89
5.3 Proposals for Risk Reduction 94
6. Recommendations 95
6.1 Developments in modelling techniques 95
6.2 Developments in test techniques 95
6.3 Developments of standards 95
6.4 Recommendations on legacy systems 96

v
 The Working Group WG01

• Approved
1997 by Agard SPP Panel

• Membership
– BELGIUM:
J. Catrysse
– CANADA:
J. Seregelyi
– FRANCE:
C. Alliot
– GERMANY:
D. Jaeger, J. Nitsch
– ITALY:
B. Audone, F. Canavero
– the NETHERLANDS:
H. Clemens
– UK:
N. Carter, I. MacDiarmid
– USA:
M. Kanda

• Coordination meetings
– 23/24 Apr. 1998: kickoff meeting (Turin, IT)
– 14 Sept. 1998: 2nd meeting (Rome, IT)
– 16 Feb. 1999: 3rd meeting (Zurich, CH)
– 25/26 Oct. 1999: 4th meeting (Turin, IT)

vi
 1

1. INTRODUCTION AND MOTIVATION

Background
The recent increasing recognition of EMC problems is based on two facts (detailed below), calling for an
activity of assessment of the state of the art and a forecast of future trends.
The first fact is the increasing number of electronic equipment in every system, and the miniaturization of the
devices that can be achieved by the new technologies. The consequence is the requirement for higher and
higher frequencies and the increased likelihood of interference. The impact on the design at system level is
evident: better tools are needed to estimate the system performance and to specify the EMC constraints,
considering that conventional rules of thumb are inadequate to describe systems which are electromagnetically
complex.
The second fact of concern about EMC in the military environment is related to the coexistence and
harmonization between commercial and military standards. In fact, military standards are mainly concerned
with the immunity of equipment and their operation in the same installation (e.g., aircraft, fixed station, etc.),
with less concern for the 'external world'. Commercial standards, on the contrary, seek a 'pacific' coexistence
of all equipment (i.e., reduced emissions and sufficient immunity).

Military Benefit
Airborne platforms are foreseen to increase the number of on-board transmitters for satellite and ground
communications, self defense, monitoring and surveillance systems. The introduction of new technologies,
relying largely on miniaturization and high speed, is triggered by the reduced weight of the equipment and the
increased bandwidth of information processing.
Procurement Agencies may experience difficulties specifying the EMC requirements of next generation
systems, because new technologies involve physical phenomena and frequency ranges of little concern in the
past. The ability to produce correct specifications must rely on the updated knowledge of the state of the art in
technology, and has a great economical impact, since reduce the risk for over/under specified systems which
prove to be costlier.

Objectives
The objective of this RSG is twofold.
State of the art of prediction techniques in EMC
The activity of the RSG will aim at the assessment of the state of the art of the techniques (both analytical and
numerical) that can be used for the prediction of system performance. Open problems which require further
investigation will also be identified.

Commercial vs. military EMC standards: future perspectives

The aim of the RSG is to provide an understanding on how military equipment can operate in a world ruled by
commercial specifications, and possibly how (and if) commercial standards (which are less expensive for the
industry to fulfill) can be adopted by military organizations.

Summary
The study has focussed on three areas of EMC design, development and qualification in future defence
systems, namely:
Numerical modelling
Test techniques
Published standards

The limitations of existing techniques and standards have been examined and highlighted. Such limitations
cause risks at the present time. However, the risks will increase as a result of changes in the commercial and
technological environment and potential increases in risk as a result of these changes in the absence of
research development, have been highlighted. Furthermore, recommendations on investment in research and
development have been made in order to mitigate the increasing risks.
This page has been deliberately left blank

Page intentionnellement blanche

 3

2. EXAMINATION OF THE LIMITATIONS OF MODELLING

AND TESTING
2.1 Description of Generic Processes.

The nature of design, development and qualification in EMC results in a process which is a well balanced
combination of designing within guidelines, modelling and testing at component, equipment and complete
system level. At the present time the balance between testing and modelling is determined by the limitations
of modelling the phenomena. This balance could be shifted with considerable business benefits if modelling
capabilities could be enhanced.

A generic EMC design, development and qualification process that applies to any system is shown in Fig.1.
The diagram shows a progression of stages of maturity of a project down the middle. The EMC activities are
shown in bold shadowed boxes on either side with arrows showing contributions to the various stages of
maturity. The final basis for qualification consists of data of five different forms, namely:

• Whole system test data

• Component & equipment test data
• Documented design guidance data
• Documented concessions against the guidance
• Modelling results

It can be seen that there is a balance of test and modelling activities in the process.

The Role of Modelling.

It can be seen that modelling contributes to the process at all stages. It is used to explore design options at the
conceptual design phase, provide the basis for equipment procurement specifications and engineering design
guides. Later in the programme detailed design options and conflicts are explored using modelling.

Finally, modelling supports the component, equipment and whole system test programmes. Such input
includes support for the design of test rigs, determination of the details of the procedure, exploration of areas
that cannot be tested (once validated) and provision of corrections to remove the effects of the test conditions.

The Role of Testing.

The role of testing at the present time is larger than is desirable as a result of the lack of capability available in
modelling. If the modelling had a wider bandwidth capability it could be used for all examination of the linear
transfer functions and testing could be limited to validating the modelling and exploration of the system
behaviours involving non-linearity and active component upset behaviour. However, due to present
limitations testing must also be used to explore the higher frequency transfer functions above 100MHz.
4

Modelling in Produce Electromagnetic

support of Concept environmental
conceptual Definition requirements for the
design whole system
(structure & Analyse/
installation Select
design) Product
Options

Produce
product &
equipment
specifications Design
EMH Design guides Consultancy
for the system supported by
structure and Produce detailed
systems installation engineering modelling
definition

Manufacture
test articles, &, Modelling in
rigs. support of the test
Design control
Equipment programme (rig &
(Concessions, programme design)
procurement
Risks etc) &
interface guide
Structural
component &
equipment qual’

Whole system
qual’ testing Modelling in
direct support of
clearance

CLEARANCE

PRODUCTION AND IN-SERVICE SUPPORT

Fig.1 The Electromagnetic Hazard Protection Design and Clearance Process Framework
 5

2.2 Numerical modelling and present limitations.

Computer techniques have revolutionized the way in which electromagnetic problems are analyzed. Antenna
and microwave engineers rely heavily on computer methods to analyze and help evaluate new designs or
design modifications. Although most EM problems ultimately involve solving only one or two partial
differential equations subject to boundary constraints, very few practical problems can be solved without the
aid of a computer.
Computer methods for analyzing problems in electromagnetics generally fall into one of three categories,
analytical techniques, numerical techniques, and expert systems. Analytical techniques make simplifying
assumptions about the geometry of a problem in order to apply a closed-form solution. Numerical techniques
attempt to solve fundamental field equations directly, subject to the boundary constraints posed by the
geometry. Expert systems do not actually calculate the field directly, but instead estimate values for the
parameters of interest based on a rules database.
A number of computer programs based on analytical techniques are available to the EMC engineer. Some are
very simple and run on personal computers. Others are very elaborate and run on supercalculators. Analytical
techniques can be a useful tool when the important EM interactions of the configuration can be anticipated.
However, most EMC problems of interest are simply too unpredictable to be modeled using this approach.
Expert systems approach a problem in much the same way as a quick-thinking, experienced EM engineer with
a calculator would approach it. As system design and board layout procedures become more automated, expert
system EM software will certainly play an important rôle. Neverthless, expert systems are no better than their
rules database and it is unlikely that they will ever be used to model or understand, for example, the complex
EM interactions that cause EMI sources to radiate.
Numerical techniques generally require more computation than anlytical techniques or expert systems, but
they are very powerful EM analysis tools. Without making a priori assumptions about which field interactions
are most significant, numerical techniques analyze the entire geometry provided as input. They calculate the
solution to a problem based on a full-wave analysis.
A number of different numerical techniques for solving electromagnetic problems are available. Each
numerical technique is well-suited for the analysis of a particular type of problem. The numerical technique
used by a particular EM analysis program plays a significant role in determining what kinds of problems the
program will be able to analyze.
This report reviews and summarize the main numerical electromagnetic modeling techniques that can be used
for analyzing electromagnetic configurations. Several references are cited to aid the reader who wishes to
investigate a particular technique in more detail.

Modeling choices in computational electromagnetics

Classification of electromagnetic problems

Problem classification is an important concept because the general theory and methods of solution usually
apply only to a given class of problems. Classifying EM problems will help engineers to answer the question
of what method is best for solving a given problem. Continuum problems are categorized differently
depending on the particular item of interest, which could be one of these :
• The solution region,
• The nature of the equation describing the problem,
• The associated boundary conditions.
It is evident that these classifications are sometimes not independent of each other.

Classification of solution regions

In terms of the solution region or problem domain, the problem could be an interior problem, also variably
called an inner, closed, or bounded problem, or an exterior problem, also variably called an outer, open, or
unbounded problem.
Consider the solution region R with boundary S, as shown in figure 2.1. If part or all of S is at infinity, R is
exterior/open, otherwise R is interior/closed. For example, wave propagation in a waveguide is an interior
problem, whereas while wave propagation in free space, scattering of EM waves by raindrops, and radiation
from a dipole antenna are exterior.
6

A problem can also be classified in terms of the electrical, constitutive properties (σ, ε, µ) of the solution
region. This solution region could be linear (or nonlinear), homogeneous (or inhomogeneous), and isotropic
(or anisotropic).

Figure 2.1: Solution region R with boundary S.

Classification of differential equations

EM problems are classified in terms of the equations describing them. The equations could be differential or
integral or both. Most EM problems can be stated in terms of an operator equation :

LΦ = g (2-1)

where L is an operator (differential, integral, or integro-differential), g is the known excitation or source, and
Φ is the unknown function to be determined.
EM problems involve linear, second-order differential equations. In general, a second-order partial differential
equation (PDE) is given by :

∂ 2Φ ∂ 2Φ ∂ 2Φ ∂Φ ∂Φ
a + b + c 2 + d +e + fΦ = g (2-2)
∂x 2
∂x∂y ∂y ∂x ∂y

The coefficients a, b, and c in general are functions of coordinates x and y ; they may also depend on Φ itself,
in which case the PDE is said to be nonlinear. Since most EM problems involve linear PDE, a, b, and c will
be regarded as constants. A PDE in which g(x,y) in equation (2-2) equals zero is termed homogeneous ; it is
inhomogeneous if g(x,y) ≠ 0. Notice that equation (2-2) has the same form as equation (2-1), where L is now a
differential operator given by :

∂2 ∂2 ∂2 ∂ ∂
L = a 2 +b +c 2 +d +e + f = g (2-3)
∂x ∂x ∂y ∂y ∂x ∂y

A PDE in general can have both boundary values and initial values. PDEs whose boundary conditions are
specified are called steady-state equations. If only initial values are specified, they are called transient
equations.
Any linear second-order PDE can be classified as elliptic, hyperbolic, or parabolic depending on the
coefficients a, b, and c. Equation (2-2) is said to be :

Elliptic if b 2 − 4 ac < 0
Hyperbolic if b 2 − 4ac > 0 (2-4)
Parabolic if b − 4ac = 0
2
 7

The terms hyperbolic, parabolic, and elliptic are derived from the fact that the quadratic equation :

ax 2 + bxy + cy 2 + dx + ey + f = 0 (2-5)

represents a hyperbola, parabola, or ellipse if b 2 − 4ac is positive, zero, or negative, respectively.

Elliptic PDEs are associated with steady-state phenomena, i.e., boundary-value problems. Typical examples of
this type of PDE include Laplace’s equation and Poisson's equation. An elliptic PDE usually models an
interior problem, and hence the solution region is usually closed or bounded.
Hyperbolic PDEs arise in propagation problems. The solution region is usually open so that a solution
advances outward indefinitely from initial conditions while always satisfying specified boundary conditions.
Parabolic PDEs are generally associated with problems in which the quantity of interest varies slowly in
comparison with the random motions which produce the variations. The most common parabolic PDE is the
diffusion equation in one dimension. Like hyperbolic PDE, the solution region for parabolic PDE is usually
open. The initial and boundary conditions typically associated with parabolic equations resemble those for
hyperbolic problems except that only one initial condition at t = 0 is necessary since the equation is only first
order in time. Also, parabolic and hyperbolic equations are solved using similar techniques, whereas elliptic
equations are usually more difficult and require different techniques.
The type of problem represented by equation (2-1) is said to be deterministic, since the quantity of interest can
be determined directly. Another type of problem where the quantity is found indirectly is called
nondeterministic or eigenvalue. The standard eigenproblem is of the form :

LΦ = λΦ (2-6)

where the source term in equation (2-1) has been replaced by λΦ . A more general version is the generalized
eigenproblem having the form :

LΦ = λ M Φ (2-7)

where M, like L, is a linear operator for EM problems. In equations (2-6) and (2-7), only some particular
values of λ called eigenvalues are permissible ; associated with these values are the corresponding solutions Φ
called eigenfunctions. Eigenproblems are usually encountered in vibration and waveguide problems where the
eigenvalues λ correspond to physical quantities such as resonance and cutoff frequencies, respectively.

Classification of boundary conditions

The problem consists of finding the unknown function Φ of a partial differential equation. In addition to the
fact that Φ satifies (2-1) within a prescribed solution region R, Φ must satisfy certain conditions on S, the
boundary of R. Usually these boundary conditions are of the Dirichlet and Neumann types. Where a boundary
has both, a mixed boundary condition is said to exist.
- Dirichlet boundary condition :

Φ(r ) = 0, r on S (2-8)

- Neumann boundary condition:

∂Φ(r )
= 0, r on S (2-9)
∂n

i.e., the normal derivative of Φ vanishes on S.

8

- Mixed boundary conditions :

∂Φ ( r )
+ h ( r )Φ ( r ) = 0, r on S (2-10)
∂n

∂Φ(r )
where h(r) is a known function and is the directional derivative of Φ along the outward normal to the
∂n
boundary S, i.e. :

∂Φ
= ∇Φ • an (2-11)
∂n

where an is a unit normal directed out of R. Note that the Neumann boundary condition is a special case of the
mixed condition with h(r) = 0. The conditions in equations (2-8) to (2-10) are called homogeneous boundary
conditions. The more general ones are the inhomogeneous :

Dirichlet :

Φ(r ) = p(r ), r on S (2-12)

Neumann :

∂Φ(r )
= q (r ), r on S (2-13)
∂n

Mixed :

∂Φ ( r )
+ h(r ) Φ(r ) = w(r ), r on S (2-14)
∂n

where p(r), q(r), and w(r) are explicitly known functions on the boundary S. For example, Φ(0) = 1 is an
inhomogeneous Dirichlet boundary condition, and the associated homogeneous counterpart is Φ(0) = 0. Also
Φ’(1) = 2 and Φ’(1) = 0 are, respectively, inhomogeneous and homogeneous Neumann boundary conditions.
In electrostatics, for example, if the value of electric potential is specified on S, we have Dirichlet boundary
∂V
condition, whereas if the surface charge ( ρs = Dn = ε ) is specified, the boundary condition is Neumann.
∂n
The problem of finding a function Φ that is harmonic in a region is called Dirichlet problem (or Neumann
∂Φ
problem) if Φ (or ) is prescribed on the boundary of the region.
∂n
It is worth observing that the term « homogeneous » has been used to mean different things. The solution
region could be homogeneous meaning that σ, ε, and µ are constant within R ; the PDE could be
homogeneous if g = 0 so that LΦ = 0 ; and the boundary conditions are homogeneous when p(r) = q(r) = w(r)
= 0.

Alternative modeling approaches available for CEM

There are four major, first principles, models in computational electromagnetics, given by:

Frequency Domain Integral Equation (FDIE) models remain the most widely studied and used models; they
were the first to receive detailed development.

Frequency Domain Differential Equation (FDDE) models, whose use has also increased considerably in
recent years, although most work to date has emphasized low-frequency applications.
 9

Time Domain Differential Equation (TDDE) models, the use of which has increased tremendously over the
past several years, primiraly as a result of much and faster computers.

Time Domain Integral Equation (TDIE) models, although available for more than 30 years, have gained
increased attention in the past decade. The recent advances in this area make these methods very attractive for
a large variety of applications.

It is worth mentioning several of the advantages in performing time domain modeling. First, wide band data
are made available from one model computation as opposed to the frequency domain approach, in which
many frequency samples are required to obtain the equivalent data. Second, it provides a more straightforward
approach in modeling impedance nonlinearities in the time domain. Third, time domain models can handle
time variations of load impedances.
Besides physical interpretability, there are two basic reasons for modeling in the time domain which provide a
distinct advantage in most applications in which transient results are available:
- The first reason is the computational efficiency: For certain problems and/or approaches, fewer arithmetic
operations are required when performed in the time domain. For example, in applications in which the early
time peak response of an object to an impulsive field is sought, a time domain model offers an intrinsically
more efficient approach compared to a frequency domain model, which requires frequency samples across a
broad bandwidth followed by a Fourier (or other) transform to obtain the desired result. When seeking
broadband information, a time domain model is also a more natural choice because it provides a transient
response whose bandwidth is limited only by the frequency content of the excitation and the time and space
sampling used in developing the model. In addition, time domain models may offer a naturally better match to
massively parallel computer architectures than do frequency domain models.
- The second reason is the problem requirement: Problems that involve nonlinear or components can usually
be modeled in a more straightforward and efficient manner in time domain, as can problems involving time-
varying media and components. An additional benefit of time domain modeling is that time gating can be used
in modeling, as in measurements, to remove the effects of unwanted reflections or to simulate larger objects.
An example of the latter application is that of replacing an infinite cylindrical antenna model with a three-
dimensional (3D) wire model whose behavior at a midpoint feed at early times, prior to end reflections, will
be identical to that of an infinite structure [2-1]. Finally, body resonances, or singularity expansion method
(SEM) poles, may be computed more directly from a time domain model.

Evolution of Time Domain Modeling

Representative examples of the growing variety of time domain research include the original TDDE approach
by Yee [2-2] which forms the basis of the widely used finite-difference time domain (FDTD) model. An
extensive survey of the application of this method is available [2-3]. A related application of a TDIE to
acoustics was presented by Mitzner [2-4]. This work was closely followed by TDIE EM applications [2-5 to
2-8]. An alternative implementation of TDDE models was shortly thereafter initiated as the transmission-line
method (TLM) by Johns and Beurle [2-9]. Recently, TD versions of the method of lines (TDML) and the
geometrical theory of diffraction (TDGTD) were presented by Nam et al. [2-10] and Veruttipong [2-11],
respectively. It seems likely that TD versions of other modeling approaches can also be expected to be
developed.
Accompanying this initial research into TD CEM models was continuing work of a more analytical nature,
including a series of papers in the early 1960s, one of which was a study by Brundell [2-12] on transient
current waves propagating azimuthally around an infinite circular cylinder. Related papers by Wu [2-13] and
Einarsson [2-14] investigated the impulse response of an infinite dipole antenna. Another fundamental
analytical study of antennas excited by impulsive sources was presented by Franceschetti and Papas [2-15],
Tijhuis et al. [2-16] reexamined a classical problem, the transient response of a thin, straight wire.
An increasing amount of TDIE modeling has followed. For example, Miller et al. [2-17] emphasized wire
applications of the electric field IE (EFIE) which is further developed together with surface modeling using
the magnetic field IE (MFIE) [2-18]. Other examples of developing TD models include Lui and Mei [2-19],
Bennett [2-20 to 2-21], Bennett and Mieras [2-22 to 2-23], Gomez et al. [2-24], Marx [2-25], Bretones et al.
[2-26], Gomez et al. [2-27 to 2-28], Rao and Wilton [2-29], Vechinski et al. [2-30 to 2-31] and Walker et al.
[2-32 to 2-33]. Application examples have grown commensurately, as demonstrated by some nonlinear
modeling [2-34 to 2-35], and as illustrated by using the time-gating feature of TD modeling for simulating
10

infinite structures with a 3D wire model [2-1]. Selective overviews of this early TD research are given by
Bennett and Ross [2-36], Miller and Landt [2-37], and Miller [2-38 to 2-39].
Althrough the literature devoted to time domain EM is rapidly expanding, there are few books devoted to the
topic. Three edited books are by Felsen [2-40], Rao [2-41] and Miller [2-42]. The two former cover a variety
of topics in time domain modeling and analysis, whereas the later systematically addresses the topic of time
domain measurements in Electromagnetics together with an associated discussion of modeling and signal
processing applications. Also, books by Kunz and Lubbers [2-43] and Taflove [2-44] are devoted exclusively
to the FDTD formulation, whereas the TLM is the topic of a book by Christopoulos [2-45]. Recent edited
books devoted to a related topic, ultra-wideband EM, include Noël [2-46], Bertoni et al. [2-47], and Taylor [2-
48], whereas Lamensdorf and Susman [2-49] presented work on pulsed antennas.

Finite Element Methods

The finite element method (FEM) has its origin in the field of structural analysis. Although the earlier
mathematical treatment of the method was provided by Courant [3-1] in 1943, the method was not applied to
electromagnetic (EM) problems until 1968. Since then the method has been employed in diverses areas such
as waveguide problems, electric machines, semiconductor devices, microstrips, and absorption of EM
radiation by biological bodies. For a review of the historical development of FEM, the interested reader is
referred to textbooks that are exclusively devoted to the FEM.
Although the finite difference method (FDM) and the method of moments (MOM) are conceptually simpler
and easier to program than the finite element method (FEM), FEM is a more powerful and versatile numerical
technique for handling problems involving complex geometries and inhomogeneous media. The systematic
generality of the method makes it possible to construct general-purpose programs for solving a wide range of
problems. Consequently, programs developed for a particular discipline have been applied successfully to
solve problems in a different field with little or no modification [3-2].
Electrical engineers use finite element methods to solve complex, nonlinear problems in magnetics and
electrostatics. Until recently however, very little practical modeling of 3-dimensional electromagnetic
radiation problems was performed using this technique. There were two reasons for this. First, practical three-
dimensional vector problems require significantly more computation than two-dimensional or scalar
problems. Second, spurious solutions known as vector parasites often result in unpredictable, erroneous
results. However, recent developments in this field [3-3, 3-4] appear to have solved the vector parasite
problem. An increasing availability of computer ressources coupled with a desire to model more complex
electromagnetic problems has resulted in a wave of renewed interest in finite element methods to solve EM
radiation problems.
The first step in finite-element analysis is to divide the configuration into a number of small homogeneous
pieces or elements. An example of a finite-element model is shown in figure 3-1. The model contains
information about the device geometry, material constants, excitations and boundary constraints. The elements
can be small where geometric details exist and much larger elsewhere. In each finite element, a simple (often
linear) variation of the field quantity is assumed. The corners of the elements are called nodes.

Figure 3.1: Finite-Element Modeling Example.

 11

The finite element analysis of any problem involves basically four steps [3-5]:
- Discretizing the solution region into finite number of subregions or elements,
- Deriving governing equations for a typical element,
- Assembling of all elements in the solution region, and
- Solving the system of equations obtained.
Most finite element methods are variational techniques. Variational methods work by minimizing or
maximizing an expression that is known to be stationary about the true solution. Generally, finite-element
analysis techniques solve for the unknown field quantities by minimizing an energy functional. The energy
functional is an expression describing all the energy associated with the configuration being analyzed. For 3-
dimensional, time-harmonic problems this functional may be represented as:
µH εE J ⋅E
2 2

F=∫ + − dν (3-1)
υ
2 2 2 jω

The first two terms in the integrand represent the energy stored in the magnetic and electric fields and the third
term is the energy dissipated (or supplied) by conduction currents.
Expressing H in terms of E and setting the derivative of this functional with respect to E equal to zero, an
equation of the form f(J,E) = 0 is obtained. A kth-order approximation of the function f is then applied at each
of the N nodes and boundary conditions are enforced, resulting in the system of equations:

 J1   y11 y12 . .   E1 
J  y y 22 . .  E 2 
 2  21  
 . =  . . . .   (3-2)
    
 .   . . . .  
 J n   . . . y nn   E n 

The values of J on the left-hand side of this equation are referred to as the source terms. They represent the
known excitations. The elements of the Y-matrix are functions of the problem geometry and boundary
constraints. Since each element only interacts with elements in its own neighborhood, the Y-matrix is
generally sparse. The terms of the vector on the right-hand side represent the unknown electric field at each
node. These values are obtained by solving the system of equations. Other parameters, such as the magnetic
field, induced currents, and power loss can be obtained from the electric field values.
In order to obtain a unique solution, it is necessary to constrain the values of the field at all boundary nodes.
For example, the metal box of the model in figure 3-1 constrains the tangential electric field at all boundary
nodes to be zero. A major weakness of the finite element method is that it is relatively difficult to model open
configurations (i.e. configurations where the fields are not known at every point on a closed boundary).
Various techniques such as ballooning and absorbing boundaries are used in practice to overcome this
defiency. These techniques work reasonably well for 2-dimensional problems, but so far they are not very
effective for 3-dimensional electromagnetic radiation problems.
The major advantage that finite element methods have over other EM modeling techniques stems from the
fact that the electrical and geometric properties of each element can be defined independently. This permits
the problem to be set up with a large number of small elements in regions of complex geometry and fewer,
larger elements in relatively open regions. Thus it is possible to model configurations that have complicated
geometries and many arbitrarily shaped dielectric regions in a relatively efficient manner.
Commercial finite element codes [3-6, 3-7] are available that have graphical user interfaces and can determine
the optimum placement of node points for a given geometry automatically. These codes are used to model a
wide variety of electromagnetic devices such as spark plugs, transformers, waveguides, and integrated
circuits.

Specific implementations of three-dimensional electromagnetic finite element codes are described in Ph.D.
dissertations by Maile [3-8] and Webb [3-9]. Silvester and Ferrari [3-10] have written an excellent text on this
subject for electrical engineers.
One of the major difficulties encountered in the finite element analysis of continuum problems is the tedious
and time-consuming effort required in data preparation. Discretization of the continuum involves dividing up
the solution region into subdomains, called finite elements. Figure 3-2 shows some typical elements for one-,
12

two-, and three-dimensional problems. Efficient finite element programs must have node and element
generating schemes, referred to collectively as mesh generators. Automatic mesh generation minimizes the
input data required to specify a problem. It not only reduces the time involved in data preparation, it
eliminates human errors introduced when data preparation is performed manually. Combining the automatic
mesh generation program with computer graphics is particularly valuable since the output can be monitored
visually. As the solution regions become more complex than the ones considered previously, the task of
developing mesh generators becomes more tedious. A number of mesh generation algorithms of varying
degrees of automation have been proposed for arbitrary solution domains. Reviews of various mesh
generation techniques can be found in [3-11, 3-12].

Figure 3-2: Typical finite elements:

a) One-dimensional,
b) Two-dimensional,
c) Three-dimensional.

The basic steps involved in a mesh generation are as follows [3-13]:

- Subdivide solution region into few quadrilateral blocks,
- Separately subdivide each block into elements,
- Connect individual blocks.
The accuracy of a finite element solution can be improved by using finer mesh or using higher order elements
or both. A discussion on mesh refinement versus higher order elements is given by Desai and Abel [3-2]; a
motivation for using higher order elements is given by Csendes in [3-14]. In general, fewer higher order
elements are needed to achieve the same degree of accuracy in the final results. The higher order elements are
particularly useful when the gradient of the field variable is expected to vary rapidly. They have been applied
with great success in solving EM-related problems [3-10, 3-14 to 3-19].

Hybrid Finite Element Methods

To apply the FEM to exterior or unbounded problems such as open-type transmission lines (e.g., microstrip),
scattering, and radiation problems poses certain difficulties. To overcome these difficulties, several
approaches [3-20 to 3-30] have been proposed, all of which have strengths and weaknesses. Two common
approaches are the infinite element method and the boundary element method.
The finite element method (FEM) and the method of moments (MOM) have become the two most popular
methods of numerical analysis of electromagnetic problems. The choice between the two numerical
techniques will usually depend on the particular problem, although both are ultimately capable of yielding the
 13

same information. The two methods result in a set of simultaneous equations. These equations look quite
different from each other, and each set of equations presents its own peculiar problems. Perhaps the best way
to compare MOM with FEM is shown in table 3.1. From the table, it is evident that the two methods have
properties that complement each other. In view of this, hybrid methods have been proposed. These methods
allow the use of both MOM and FEM with the aim of exploiting the strong points in each method.

Table: Comparison between Method of Moments and Finite Element Method [3-31]

One of these hybrid methods involves using the so-called boundary element method (BEM). It is a finite
element approach for handling exterior problems [3-26 to 3-30]. It basically involves obtaining the boundary-
integral equation from Green's identity and solving this by a discretization procedure similar to that used in
regular finite element analysis. Since the BEM is based on the boundary integral equivalent to the governing
differential equation, only the surface of the problem domain needs to be modeled. Thus the dimension of the
problem is reduced by one as in MOM. For 2-D problems, the boundary elements are taken to be straight line
segments, whereas for 3-D problems, they are taken as triangular elements. Thus the shape or interpolation
functions corresponding to subsectional bases in the MOM are used in the finite element analysis.

Concluding remarks on FEM

The finite element method has been applied with great success to numerous EM-related problems. Such
applications are :
• Transmission line problems,
• Optical and microwave waveguide problems,
• Electric machines,
• Semiconductor devices,
• Scattering problems,
• Human exposition to EM radiation,
• Others.

Moment Methods
Like finite-element analysis, the method of moments (or moment method) is a technique for solving complex
integral equations by reducing them to a system of simpler linear equations. In contrast to the variational
approach of the finite element method however, moment methods employ a technique known as the method of
weighted residuals. Actually, the terms method-of-moments and method-of-weighted-residuals are
synonymous. Harrington [4-1] was largely responsible for popularizing the term method of moments in the
14

field of electrical engineering. His pioneering efforts first demonstrated the power and flexibility of this
numerical technique for solving problems in electromagnetics.
All weighted residual techniques begin by establishing a set of trial solutions functions with one or more
variable parameters. The residuals are a measure of the difference between the trial solution and the true
solution. The variable parameters are determined in a manner that guarantees a best fit of the trial functions
based on a minimization of the residuals.
The equation solved by moment method techniques is generally a form of the electric field integral equation
(EFIE) or the magnetic field integral equation (MFIE). Both of these equations can be derived from
Maxwell's equations by considering the problem of a field scattered by a perfect conductor (or a lossless
dielectric). These equations are of the form:

EFIE: E = f e ( J ) (4-1)
MFIE: H = f m ( J ) (4-2)

where the terms on the left-hand side of these equations are incident field quantities and J is the induced
current.
The form of the integral equation used determines which types of problems a moment-method technique is
best suited to solve. For example one form of the EFIE may be particularly well suited for modeling thin-wire
structures, while another form is better suited for analysing metal plates. Usually these equations are
expressed in the frequency domain, however the method of moments can also be applied in the time domain.
The first step in the moment-method solution process is to expand J as a finite sum of basis (or expansion)
functions:

M
J = ∑ Jib i (4-3)
i =1

where bi is the ith basis function and Ji is an unknown coefficient.

Next, a set of M linearly independent weighting (or testing) functions, wj, are defined. An inner product of
each weighting function is formed with both sides of the equation being solved. In the case of the MFIE
(Equation 4-2), this results in a set of M independant equations of the form:

〈 w j , H〉 = 〈 w j , f m ( J ) 〉 j = 1,2,....,M (4-4)

By expanding J using equation (4-3), we obtain a set of M equations in M unknowns:

M
〈 w j , H〉 = ∑ 〈 w j , f m ( J i , b i )〉 j = 1,2,....,M (4-5)
i =1

This can be written in matrix form as:

[H] = [ Z ][ J ] (4-6)

where: Zij = 〈 w j , f m (bi )〉

J i = Ji
H j = 〈 w j , H inc 〉

The vector H contains the known incident field quantities and the terms of the Z-matrix are functions of the
geometry. The unknown coefficients of the induced current are the terms of the J vector. These values are
obtained by solving the system of equations. Other parameters such as the scattered electric and magnetic
fields can be calculated directly from the induced currents.
Depending on the form of the field integral equation used, moment methods can be applied to configurations
of conductors only, homogeneous dielectrics only, or very specific conductor-dielectric geometries. Moment
method techniques applied to integral equations are not very effective when applied to arbitrary configurations
 15

with complex geometries or inhomogeneous dielectrics. They also are not well-suited for analyzing the
interior of conductive enclosures or thin plates with wire attachments on both sides [4-2].
Nevertheless, moment method techniques do an excellent job of analyzing a wide variety of important three-
dimensional electromagnetic radiation problems. General purpose moment method codes are particurlarly
efficient at modeling wire antennas or wires attached to large conductive surfaces. They are widely used for
antenna and electromagnetic scattering analysis. Several non-commercial general-purpose moment-method
computer programs are available [4-3, 4-4].

Concluding remarks on MOM

The method of moments is a powerful numerical method capable of applying weighted residual techniques to
reduce an integral equation to a matrix equation. The solution of the matrix equation is usually carried out via
inversion, elimination, or iterative techniques. Although MOM is commonly applied to open problems such as
those involving radiation and scattering, it has been successfully applied to closed problems such as
waveguides and cavities.
General concepts on MOM are covered in [4-5] and [4-6]. Clear and elementary discussions on the IEs and
Green's functions may be found in [4-7 to 4-13]. For further study on the theory of the method of moments,
one should see [4-1, 4-5, 4-8, 4-14, 4-15].
The number of problems that can be treated by MOM is endless. The following problems represent typical
EM-related application areas:
• Electrostatic problems,
• Wire antennas and scatterers,
• Scattering and radiation from bodies of revolution,
• Scattering and radiation from bodies of arbitrary shape,
• Transmission lines,
• Aperture problems,
• Biomagnetic problems.
A number of user-oriented computer programs have evolved over the years to solve electromagnetic integral
equations by the method of moments. These codes can handle radiation and scattering problems in both the
frequency and time domains. Reviews of the code may be found in [4-16 to 4-18]. The most popular of these
codes is the Numerical Electromagnetic Code (NEC) developed at the Lawrence Livermore National
Laboratory [4-16, 4-19]. NEC is a frequency domain antenna modeling FORTRAN IV code applying the
MOM to IEs for wire and surface structures. Its most notable features are probably that it is user oriented,
includes documentation, and is available; for these reasons, it is being used in public and private institutions.
A compact version of NEC is the mini-numerical electromagnetic code (MININEC) [4-20], which is intented
to be used in personal computers.
It is important that we recognize the fact that MOM is limited in applications to radiation and scattering from
bodies that are electrically large. The size of the scatterer or radiator must be of the order of λ3. This is
because the cost of storing, inverting, and computing matrix elements becomes prohibitively large. At high
frequencies, asymptotic techniques such as the geometrical theory of diffraction (GTD) are usually employed
to derive approximate but accurate solutions [4-21 to 4-23].

Finite Difference Time Domain Method

The Finite Difference Time Domain (FDTD) method is a direct solution of Maxwell's time dependent curl
equations:

∂H
∇ × E = −µ (5-1)
∂t

∂E
∇ × H = σE + ε (5-2)
∂t

It uses simple central-difference approximations to evaluate the space and time derivatives [5-1 to 5-7].
16

The FDTD method is a time stepping procedure. Inputs are time-sampled analog signals. The region being
modeled is represented by two interleaved grids of discrete points. One grid contains the points at which the
magnetic field is evaluated. The second grid contains the points at which the electric field is evaluated.
A basic element of the FDTD space lattice is illustrated in figure 5-1. Note that each magnetic field vector
component is surrounded by four electric field components. A first-order central-difference approximation can
be expressed as:

1
A
[ ] [µ
]
Ez1 ( t ) + E y 2 ( t ) − Ez 3 ( t ) − E y 4 ( t ) = − 0 Hx 0. ( t + ∆t ) − Hx 0. ( t − ∆t ) (5-3)
2 ∆t

where A is the area of the near face of the cell in figure 5-1. Hx 0. ( t + ∆t ) is the only unknown in this
equation, since all other quantities were found in a previous time step. In this way, the electric field values at
time t are used to find the magnetic field values at time t+∆t. A similar central-difference approximation of
equation (5-2) can then be applied to find the electric field values at time t+2∆t from the magnetic values at
time t+∆t. By alternately calculating the electric and magnetic fields at each time step, fields are propagated
throughout the grid.

Figure 5-1: Basic Element of the FDTD Space Lattice.

Time stepping is continued until a steady state solution or the desired response is obtained. At each time step,
the equations used to update the field components are fully explicit. No system of linear equations must be
solved. The required computer storage and running time is proportional to the electrical size of the volume
being modeled and the grid resolution.
Figure 5-2 illustrates an arbitrary scatterer embedded in a FDTD space lattice. Special absorbing elements are
used at the outer boundary of the lattice in order to prevent unwanted reflexion of signals that reach this
boundary [5-8 to 5-15]. Values of µ, ε and σ assigned to each field component in each cell define the position
and electrical properties of the scatterer. These parameters can have different values for different field
orientations permitting anisotropic materials to be modeled. Their values can also be adjusted at each time-
step depending on conditions making it easy to model nonlinear materials.
 17

Figure 5-2 : Arbitrarily shaped three-dimensional material scatterer embedded in a FDTD structured space
lattice.

Because the basic elements are cubes, curved surfaces on a scatterer must be staircased. For many
configurations this does not present a problem. However for configurations with sharp, acute edges, an
adequately staircased approximation may require a very small grid size. This can significantly increase the
computational size of the problem. Surface conforming FDTD techniques with non-rectangular elements have
been introduced to combat this problem. One of the more promising of these techniques, which permits each
element in the grid to have an arbitrary shape, is referred to as the Finite-Volume Time-Domain (FVTD)
method [5-16 to 5-29]. Figure 5-3 shows an example of meshing used for FVTD method.

Figure 5-3: Meshing of an airplane.

Frequency domain results can be obtained by applying a discrete Fourier transform to the time domain results.
This requires additional computation, but a wide-band frequency-domain analysis can be obtained by
transforming the system's impulse response.
The FDTD and FVTD methods are widely used for radar cross section analysis although they have been
applied to a wide range of EM modeling problems [5-30 to 5-40]. Their primary advantage is their great
flexibility. Arbitrary signal waveforms can be modeled as they propagate through complex configurations of
conductors, dielectrics, and lossy non-linear non-isotropic materials [5-41 to 5-47]. These techniques have
also been developped in the frequency domain [5-48]. Another advantage of these techniques is that they are
readily implemented on massively parallel computers, particularly vector processors and SIMD (single-
instruction-multiple-data) machines.
The only significant disadvantage of this technique, is that the problem size can easily get out of hand for
some configurations. The fineness of the grid is generally determined by the dimensions of the smallest
features that need to be modeled. The volume of the grid must be great enough to encompass the entire object
and most of the near field. Large objects with regions that contain small, complex geometries may require
large, dense grids. When this is the case, other numerical techniques may be much more efficient than the
FDTD or FVTD methods alone : a good approach is to combine the FVTD method with the standard FDTD
method [5-49, 5-50]. Indeed, with the finite-volume method, we can use an unstructured conformal mesh to
18

represent the object and its immediate neighborhood with relatively few cells. With the finite-difference
method, we can use a structured mesh for the remaining part of the computational domain and apply an
efficient boundary condition, for example, the PML formalism [5-9, 5-10] which reduces considerably the
number of unknowns. The gain in CPU time can also be improved for both methods by using a local time
step. For the finite-volume method, the stability condition on the time step leading to a convergent numerical
scheme is :

 
 
Vi 
dt ≤ min 
1
(5-4)
i v mi 


∑
k =1
Sk 

where Vi is the volume of the cell Vi, mi is the number of faces enclosing the cell Vi , Sk is the surface of the
face k, and v is the speed of light in the medium. For the finite-difference scheme of Yee, this condition is
given by :

 
 
1 1 
dt ≤ min 
1 
(5-5)
i v 1 1
 + +
 dx i2 dy i2 dz i2 

where dxi, dyi, and dzi are the lengths of the edges of a rectangular cell in the grid.
We observe that the stability criterion for the finite-volume method is generally more restrictive than that for
the finite-difference method. This implies that if we can use the two different time steps for each numerical
scheme, we can expect a reduction in CPU time.

Accuracy and stability of FD solutions

The question of accuracy and stability of numerical methods is extremely important if the solution is to be
reliable and useful. Accuracy has to do with the closeness of the approximate solution to exact solutions
(assuming they exist). Stability is the requirement that the scheme does not increase the magnitude of the
solution with increase in time.
They are three sources of errors that are nearly unavoidable in numerical solution of physical problems:
• Modeling errors,
• Truncation (or discretization) errors,
• Roundoff errors.
Each of these error types will affect accuracy and therefore degrade the solution. The modeling errors are due
to several assumptions made in arriving at the mathematical model. For example, a nonlinear system may be
represented by a linear PDE. Truncation errors arise from the fact that in numerical analysis, we can deal only
with a finite number of terms from processes which are usually described by infinite series. For example, in
deriving finite difference schemes, some higher-order terms in the Taylor series expansion were neglected,
thereby introducing truncation error. Truncation errors may be reduced by using finer meshes, that is, by
reducing the mesh size and time increment. Alternatively, truncation errors may be reduced by using a large
number of terms in the series expansion of derivatives, that is, by using higher-order approximations.
However, care must be exercised in applying higher-order approximations. Instability may result if we apply a
difference equation of an order higher than the PDE being examined. These higher-order difference equations
may introduce "spurious solutions".
Roundoff errors reflect the fact that computations can be done only with a finite precision on a computer. This
unavoidable source of errors is due to the limited size of registers in the arithmetic unit of the computer.
Roundoff errors can be minimized by the use of double-precision arithmetic. The only way to avoid roundoff
errors completely is to code all operations using integer arithmetic. This is hardly possible in most practical
situations.
Although it has been noted that reducing the mesh size will increase accuracy, it is not possible to indefinitely
reduce the mesh size. Decreasing the truncation error by using a finer mesh may result in increasing the
 19

roundoff error due to the increased number of arithmetic operations. A point is reached where the minimum
total error occurs for any particular algorithm using any given word length [5-51]. This is illustrated in figure
5-4. The concern about accuracy leads us to question whether the finite difference solution can grow
unbounded, a property termed the instability of the difference scheme. A numerical algorithm is said to be
stable if a small error at any stage produces a smaller cumulative error. It is unstable otherwise. The
consequence of instability (producing unbounded solution) is disastrous. To determine whether a finite
difference scheme is stable, we define an error, εn, which occurs at time step n, assuming that there is one
independent variable. We define the amplification of this error at time step n+1 as:

ε n +1 = gε n (5-6)

where g is known as the amplification factor.

The problems of stability and convergence of finite difference solutions are further discussed in [5-52, 5-53],
while the error estimates in [5-54].

Figure 5-4: Error as a function of the mesh size.

Concluding remarks
As noted previously, the finite difference method has some inherent advantages and disadvantages. It is
conceptually simple and easy to program. The finite difference approximation to a given PDE is by no means
unique; more accurate expressions can be obtained by employing more elaborate and complicated formulas.
However, the relatively simple approximations may be employed to yield solutions of any specified accuracy
simply by reducing the mesh size provided that the criteria for stability and convergence are met.
A very important difficulty in finite differencing of PDEs, especially parabolic and hyperbolic types, is that if
one value of the function Φ under study is not calculated and therefore set equal to zero by mistake, the
solution may become unstable.
A serious limitation of the finite difference method is that interpolation of some kind must be used to
determine solutions at points not on the grid.

Finite Difference Frequency Domain Method

Although conceptually the Finite Difference Frequency Domain (FDFD) method is similar to the Finite
Difference Time Domain (FDTD) method, from a practical standpoint it is more closely related to the finite
element method. Like FDTD, this technique results from a finite difference approximation of Maxwell's curl
equations. However, in this case the time-harmonic versions of these equations are employed:

∇ × E = − jωµH (6-1)
20

∇ × H = (σ + jωε )E (6-2)

Since there is no time stepping it is not necessary to keep the mesh spacing uniform. Therefore optimal FDFD
meshes generally resemble optimal finite element meshes. Like the moment-method and finite-element
techniques, the FDFD technique generates a system of linear equations. The corresponding matrix is sparse
like that of the finite element method.
Although it is conceptually much simpler than the finite element method, very little attention has been devoted
to this technique in the literature. Perhaps this is due to the head start that finite element techniques achieved
in the field of structural mechanics.
There are apparently very few codes available that utilize this technique. A notable exception is the FDFD
module that is included in the GEMACS software marketed by Advanced Electromagnetics [6-1].

Transmission Line Matrix Method

The link between field theory and circuit theory, the major theories on which electrical engineering is based,
has been exploited in developing numerical techniques to solve certain types of partial differential equations
arising in field problems with the aid of equivalent electrical networks. There are three ranges in the frequency
spectrum for which numerical techniques for field problems in general have been developed. In terms of the
wavelenght λ and the approximate dimension l of the apparatus, these ranges are:

• λ >> l
•λ # l
• λ << l.

In the first range, the special analysis techniques are known as circuit theory, in the second, as microwave
theory, and in the third, as geometric optics (frequency independent). Hence the fundamental laws of circuit
can be obtained from Maxwell's equations by applying an approximation valid when λ >> l. However, it
should be noted that circuit theory was not developed by approximating Maxwell's equations, but rather was
developed independently from experimentally obtained laws. The connection between circuit theory and
Maxwell's equations (summarizing field theory) is important; it adds to the comprehension of the
fundamentals of electromagnetics. In fact, circuits are mathematical abstractions of physically real fields;
nevertheless, electrical engineers at times feel they understand circuit theory more clearly than fields.
The idea of replacing a complicated electrical system by a simple equivalent circuit goes back to Kirchhoff
and Helmholtz. As a result of Park's [7-1], Kron's [7-2, 7-3] and Schwinger's [7-4, 7-5] works, the power and
flexibility of equivalent circuits become more obvious to engineers. The recent applications of this idea to
scattering problems, originally due to Johns [7-6], has made the method more popular and attractive.

TLM basic concepts

The Transmission Line Matrix (TLM) method is similar to the FDTD method in terms of its capabilities, but
its approach is unique. Like FDTD, analysis is performed in the time domain and the entire region of the
analysis is gridded. Instead of interleaving E-field and H-field grids however, a single grid is established and
the nodes of this grid are interconnected by virtual transmission lines. Excitations at the source nodes
propagate to adjacent nodes through these transmission lines at each time step.
The symmetrical condensed node formulation introduced by Johns [7-7] has become the standard for three-
dimensional TLM analysis. The basic structure of the symmetrical condensed node is illustrated in figure 7-1.
Each node is connected to its neighboring nodes by a pair of orthogonally polarized transmission lines.
Generally, dielectric loading is accomplished by loading nodes with reactive stubs. These stubs are usually
half the length of the mesh spacing and have a characteristic impedance appropriate for the amount of loading
desired. Lossy media can be modeled by introducing loss into the transmission line equations or by loading
the nodes with lossy stubs. Absorbing boundaries are easily constructed in TLM meshes by terminating each
boundary node transmission line with its characteristic impedance.
 21

Figure 7-1: The Symmetrical Condensed Node.

Like other numerical techniques, the TLM method is a discretization process. Unlike other methods such as
finite difference and finite element methods, which are mathematical discretization approaches, the TLM is a
physical discretization approach. In the TLM, the discretization of a field involves replacing a continuous
system by a network or array of lumped elements. For example, consider the one-dimensional system (a
conducting wire) with no energy storage as in figure 7-2a. The wire can be replaced by a number of lumped
resistors providing a discretized equivalent in figure 7-2b. The discretization of the two-dimensional,
distributed field is shown in figure 7-3.

Figure 7-2: a) One-dimensional conducting system,

b) Discretized equivalent.

Figure 7-3 : a) Two-dimensional conductive sheet,

b) Partially discretized equivalent,
c) Fully discretized equivalent.
22

The TLM method involves dividing the solution region into a rectangular mesh of transmission lines.
Junctions are formed where the lines cross forming impedance discontinuities. A comparison between the
transmission-line equations and Maxwell's equations allows equivalence to be drawn between voltages and
currents on the lines and electromagnetic fields in the solution region. Thus, the TLM method involves two
basic steps:
• Replacing the field problem by the equivalent network and deriving analogy between the field and network
quantities.
• Solving the equivalent network by iterative methods.
Figure 7-4 represents the dispersion curve of the velocity of waves in a two-dimensional TLM network. From
this figure, we conclude that the TLM can represent Maxwell’s equations over the range of frequencies from
zero to the first network cutoff frequency, which occurs at ω∆l/c = π/2 or ∆l/λ = ¼. Over this range, the
velocity of the waves behaves according to the characteristic of figure 7-4. For frequencies much smaller than
the network cutoff frequency, the propagation velocity approximates to 1 2 of the free-space velocity.

Figure 7-4 : Dispersion of the velocity of waves in a two-dimensional TLM network.

The dispersion relation for three-dimensional problems can be derived as :

 π ∆l   ∆l 
sin  ⋅  = 2 sin  π  (7-1)
r λ  λ

where r represents the normalized propagation velocity (r = un/c).

Thus for low frequencies (∆l/λ<0.1), the network propagation velocity in three-dimensional space may be
considered constant and equal to c/2.

Error sources and corrections

As in all approximate solutions such as the TLM technique, it is important that the error in the final result be
minimal. In the TLM method, four principal sources of error can be identified:
• Truncation error,
• Coarseness error,
• Velocity error,
• Misalignment error.
Each of these sources of error and ways of minimizing it will be discussed in what follows.

Truncation error
The truncation error is due to the need to truncate the impulse response in time. As a result of the finite
duration of the impulse response, its Fourier transform is not a line spectrum but rather a superposition of
 23

sinx/x functions, which may interfere with each other and cause a slight shift in their maxima.The maximum
truncation error is given by :

∆S 3λc
eT = = (7-2)
∆l λc SN 2 π 2 ∆l

where λc is the cutoff wavelength to be calculated. ∆S is the absolute error in ∆l/λc, S is the frequency
separation (expressed in terms of ∆l/λc, λc being the free-space wavelength) between two neighboring peaks as
shown in figure 7-5, and N is the number of iterations. Equation (7-2) indicates that eT decreases with
increasing N and increasing S. It is therefore desirable to make N large and suppress all unwanted modes close
to the desired mode by carefully selecting the input and output points in the TLM mesh. An alternative way of
reducing the truncation error is to use a Hanning window in the Fourier transform [7-8, 7-9].

Figure 7-5 : Source of truncation error :

a) Truncated output impulse,
b) Resulting truncation error in the frequency domain.

Coarseness error
This occurs when the TLM mesh is too coarse to resolve highly nonuniform fields as can be found at corners
and edges. An obvious solution is to use a finer mesh (∆l→0), but this would lead to large memory
requirements and there are limits to this refinement. A better approach is to use variable mesh size so that a
higher resolution can be obtained in the nonuniform field region [7-10]. This approach requires more
complicated programming.

Velocity error
This stems from the assumption that propagation velocity in the TLM mesh is the same in all directions and
equal to un = u 2 , where u is the propagation velocity in the medium filling the structure. The assumption
is only valid if the wavelength λn in the TLM mesh is large compared with the mesh size ∆l ( ∆l λn < 01 . ).
Thus the cutoff frequency fcn in the TLM mesh is related to the cutoff frequency fc of the real structure
according to f c = f cn 2 . If ∆l is comparable with λn, the velocity of propagation depends on the direction
and the assumption of constant velocity results in a velocity error in fc. Fortunately, a measure to reduce the
coarseness error takes care of the velocity error as well.

Misalignment error
This error occurs in dielectric interfaces in three-dimensional inhomogeneous structures such as microstrip or
fin line. Ait is due to the manner in which boundaries are simulated in a three-dimensional TLM mesh ;
dielectric interfaces appear halfway between nodes, while electric and magnetic boundaries appear across
24

such nodes. If the resulting error is not acceptable, one must make two computations, one with recessed and
one with protruding dielectric, and take the average of the results.

Concluding remarks
Transmission-line modelling (TLM), otherwise known as the transmission-line-matrix method, is a numerical
technique for solving field problems using circuit equivalent. It is based on the equivalence between
Maxwell's equations and the equations for voltages and currents on a mesh of continuous two-wire
transmission lines. The main feature of this method is the simplicity of formulation and programming for a
wide range of applications [7-8]. As compared with the lumped network model, the transmission-line model is
more general and performs better at high frequencies where the transmission and reflection properties of
geometrical discontinuities cannot be regarded as lumped [7-4].
A comparison of the TLM method with the finite difference method can be interesting. While TLM provides a
physical model, finite difference provides a mathematical model. According to Johns, the two methods
complement each other rather than compete with each other [7-11].
The advantage of using the TLM method are similar to those of the FDTD method. Complex nonlinear
materials are readily modeled. Impulse responses and the time-domain behavior of systems are determined
explicitly. And, like FDTD, this technique is suitable for implementation on massively parallel machines. A
major advantage of the TLM method , as compared with other numerical techniques, is the ease with which
complicated structures can be analysed. The great flexibility and versatility of the method reside in the fact
that the TLM mesh incorporates the properties of EM fields and their interaction with the boundaries and
material media. Hence, the EM problem need not be formulated for every new structure. Thus a general-
purpose program such as in [7-12] can be developed such that only the parameters of the structure need be
entered for computation. Another advantage of using the TLM method is that certain stability properties can
be deduced by inspection of the circuit. There are no problems with convergence, stability, or spurious
solutions.
The disadvantage of the FDTD method are also shared by this technique. The primary disadvantage being that
voluminous problems that must use a fine grid require excessive amounts of computation.
Nevertheless, both the TLM and FDTD techniques are very powerful and widely used. For many types of EM
problems they represent the only practical methods of analysis. Deciding whether to utilize a TLM or FDTD
technique is a largely personal decision. Many engineers find the transmission line analogies of the TLM
method to be more intuitive and easier to work with. On the other hand, others prefer the FDTD method
because of its simple, direct approach to the solution of Maxwell's field equations. The TLM method requires
significantly more computer memory per node, but it generally does a better job of modeling complex
boundary geometries. This is because both E and H are calculated at every boundary node.
A listing for a general purpose TLM code written in FORTRAN can be found in a Ph.D. dissertation by S.
Akhtarzad [7-12]. This program can be adapted to a variety of applications. A general overview of the TLM
method and a two-dimensional TLM code is provided in a book by Hoefer [7-13].

Generalized Multipole Technique

The Generalized Multipole Technique (GMT) is a relatively new method for analyzing EM problems. It is a
frequency domain technique that (like the method of moments) is based on the method of weighted residuals.
However, this method is unique in that the expansion functions are analytic solutions of the fields generated
by sources located some distance away from the surface where the boundary condition is being enforced.
Moment methods generally employ expansion functions representing quantities such as charge or current that
exist on a boundary surface. The expansion functions of the Generalized Multipole Technique are spherical
wave field solutions corresponding to multipole sources. By locating these sources away from the boundary,
the field solutions form a smooth set of expansion functions on the boundary and singularities on the boundary
are avoided.
Like the method of moments, a system of linear equations is developed and then solved to determine the
coefficients of the expansion functions that yield the best solution. Since the expansion functions are already
field solutions, it is not necessary to do any further computation to determine the fields. Conventional moment
methods determine the currents and/or charges on the surface first and then must integrate these quantities
over the entire surface to determine the fields. This integration is not necessary at any stage of the GMT
solution.
There is little difference in the way dielectric and conducting boundaries are treated by the GMT. The same
multipole expansion functions are used. For this reason, a general purpose implementation of the GMT
 25

models configurations with multiple dielectrics and conductors much more readily than a general purpose
moment-method technique. On the other hand, moment method techniques which employ expansion functions
that are optimized for a particular type of configuration (e.g. thin wires), are generally much more efficient at
modeling that specific type of problem.
Over the last ten years, the GMT has been applied to a variety of EM configurations including dielectric
bodies [8-1, 8-2], obstacles in waveguides [8-3], and scattering from perfect conductors [8-4, 8-5]. Work in
this young field is continuing and new developments are regularly announced. Recent significant
developments include the addition of a thin-wire capability [8-6, 8-7] and a "ringpole" expansion function for
modeling symmetric structures [8-8].
A commercial GMT code has been developed at the Swiss Federal Institute of Technology. This code is called
the MMP (Multiple MultiPole) code. A two-dimensional PC version is available through Artech House
Publishers [8-9]. A comprehensive text describing the GMT technique and the MMP code is also available [8-
10].

Conjugate Gradient Method

The Conjugate Gradient Method is another technique based on the method of weighted residuals. It is very
similar conceptually to conventional moment method techniques. Nevertheless, there are two features that
generally distinguish this technique from other moment methods. The first has to do with the way in which the
weighting functions are utilized. The second involves the method of solving the system of linear equations.
Conventional moment methods define the inner product of the weighting functions, wj, with another function
g as:

〈 w j , g 〉 = ∫ 〈 w j ⋅ g )dS (9-1)
S
This is referred to as the symmetric product. The conjugate gradient method uses a different form of the inner
product called the Hilbert inner product. This is defined as:

〈 w j , g 〉 = ∫ 〈 w j ⋅ g ∗ )dS (9-2)
S

where the * denotes complex conjugation. If both functions are real, these two definitions are equivalent.
However, when complex weighting functions are utilized, the symmetric product is a complex quantity and
therefore not a valid norm. In this case, the Hilbert inner product is preferred [9-1].
The other major difference between conventional moment methods and the conjugate gradient method
involves the technique used to solve the large system of equations these methods generate. Conventional
moment method techniques generally employ a Gauss-Jordan method or another direct solution procedure.
Direct solution techniques solve the system of equations with a given number of calculations (generally
O[N3], where N is the order of the matrix).
Conjugate gradient methods utilize an iterative solution procedure. This procedure, called the method of
conjugate gradients, can be applied to the system of equations or it can be applied directly to the operator
equation [9-2]. Iterative solution procedures such as the method of conjugate gradients are most advantageous
when applied to large, sparse matrices.

Boundary Element Method

The Boundary Element Method (BEM) is a weighted residual technique. It is essentially a moment-method
technique whose expansion and weighting functions are defined only on a boundary surface. Most general
purpose moment-method EM modeling codes employ a boundary element method [10-1, 10-4].
Like the finite element method, its origins are in the field of structural mechanics. Electrical engineers are
likely to use the more general term moment method to describe an implementation of this technique. Outside
of electrical engineering however, the terms boundary element method or boundary integral element method
are commonly used.
26

High frequency methods

In many practical high frequency scattering problems, the scatterers are very large compared to wavelength.
When high frequency radar cross section (RCS) is required, exact solution is impossible with current
computer ressources. In this cases, approximate methods are very helpful. Typical approximate techniques are
geometric optics (GO), physical optics (PO), geometric theory of diffraction (GTD), and physical theory of
diffraction (PTD). These approximations have been incorporated into the shooting and bouncing ray (SBR)
method [11-1].

Uniform Theory of Diffraction

The Uniform Theory of Diffraction (UTD) is an extension of the Geometrical Theory of Diffraction (GTD).
Both of these techniques are high-frequency methods. They are only accurate when the dimensions of objects
being analyzed are large relative to the wavelength of the field. In general, as the wavelengths of an
electromagnetic excitation approach zero, the fields can be determined using geometic optics. UTD and GTD
are extensions of geometric optics that include the effects of diffraction.
Diffraction is a local phenomena at high frequencies. Therefore, the behavior of the diffracted wave at edges,
corners, and surfaces can be determined from an asymptotic form of the exact solution for simpler canonical
problems. For example, the diffraction around a sharp edge is found by considering the asymptotic form of the
solution for an infinite wedge. GTD and UTD methods add diffracted rays to geometric optical rays to obtain
an improved estimate of the exact field solution.
The Basic Scattering Code (BSC) is a popular implementation of UTD. It is available from the ElectroScience
Laboratory of the Ohio State University [11-2].

Fast far field approximation (FAFFA)

Another RCS estimation technique, called the fast far field approximation (FAFFA), has been developed [11-
3]. The idea of this method is to compute the interactions between elements using different methods
depending on the electrical distance between the elements. When the distance is small, exact interaction is
calculated ; when the distance is large, a far field approximation is used. The field interactions are calculated
iteratively using conjugate gradient (CG) method. The iteration process is equivalent to taking into account
the higher order terms in GO, PO or PTD approximations. After several iterations, the results are found to be
greatly improved over that of a simple PO or GO. On the other hand, this method can deal with small scale
target geometry variations since it computes the near field interaction exactly hence it is more flexible to be
applied to arbitrary complex targets. This algorithm has a computational complexity of O(N1.33) and memory
requirement of O(N) for N unknown problems. The method differs from exact method since far field
approximation is used. It also differs from pure PO since the solution is calculated iteratively so that the
higher order scattering field, such as edge diffraction, surface wave and multiple-reflection, are automatically
taken into account.

Hybrid Techniques
It is apparent from the previous sections that none of the techniques described is well-suited to all (or even
most) electromagnetic modeling problems. Most moment method codes won't model inhomogeneous,
nonlinear dielectrics. Finite element codes can't efficiently model large radiation problems. GMT and UTD
codes are not appropriate for small, complex geometries or problems that require accurate determination of
the surface and wire currents. Unfortunately, most practical printed circuit card radiation models have all of
these features and therefore cannot be analyzed by any of these techniques.
One solution, which has been employed by a number of researchers, is to combine two or more techniques
into a single code. Each technique is applied to the region of the problem for which it is best suited. The
appropriate boundary conditions are enforced at the interfaces between these regions. Normally a surface
integral technique such as the boundary element method will be combined with a finite method such as the
finite element, FDTD, or TLM method. Several successful implementations of hybrid techniques are
described in the literature [12-1, 12-10].
So far, none of the available hybrid techniques model the radiation from printed circuit cards very well. This
is due to the fact that most of these methods were developed to predict radar cross section (RCS) values or for
other scattering problems where the source is remote from the configuration being modeled. Work in this area
is continuing however. Several researchers are involved in efforts to develop hybrid techniques that can be
applied to a variety of presently intractable problems.
 27

Advances in the development and implementation of codes based on a single technique continue to be
important. However, there will always be problems that defy analysis by any one technique.
Hybrid methods permit numerical modeling techniques to be applied to a whole new class of configurations.

New numerical modelling techniques

Fast Multipole Method (FFM)
As shown in chapter 4, the EM field scattering by arbitrarily shaped conductor can be obtained by finding the
solution of an integral equation where the unknown function is the induced current distribution. The integral
equation is discretized into a matrix equation by the method of moments (MOM). The resultant matrix
equation is then solved by Gaussian elimination, which requires O(N3) floating-point operations if Gaussian
elimination is used to solve N linear equations, or O(N2) operations per iteration if the conjugate gradient
(CG) method is used.
The fast multipole method (FMM) [13-1 to 13-6] speeds up the matrix-vector multiply in the conjugate
gradient (CG) method when it is used to solve the matrix equation iteratively. FMM can be applied with the
electric field integral equation (EFIE), the magnetic field integral equation (MFIE), and the combined field
integral equation (CFIE). A FMM formula for CFIE has been derived, which reduces the complexity of a
matrix-vector multiply from O(N2) to O(N1.5), where N is the number of unknowns. With a nonnested method,
using the ray-propagation fast multipole algorithm (RPFMA) [13-5, 13-6], the cost of a FMM matrix-vector
multiply is reduced to O(N4/3). The authors of this technique have also implemented a multilevel fast
multipole algorithm (MLFMA), whose complexity is further reduced to O(NlogN) [13-7]. To test the
complexity, the electromagnetic scattering from a conducting sphere has been calculated using the combined-
field integral equation (CFIE). The machine was the SGI Power Challenge with 4 processors (R8000) and 2
GB of memory. However, only one processor has been used for this simulation. The diameter of the sphere
varied from 1.5 λ to 24 λ, the number of unknowns (N) ranged from 2352 to 602112, while the number of
levels in MLFMA was from three to seven. The longest edge length was 0.15 λ, while the average edge length
was 0.10 λ. The CPU time per iteration and the memory requirements are plotted as functions of the number
of unknowns in figure 13-1. Two curves, 8x10-5NlogN and 2.7x10-3N, are also plotted in the same figure, for
comparison. A total of 602112 unknowns, with a seven-level MLFMA, was used in the last point in figure 13-
1. It consumed 12 hours on the Power Challenge using one processor {six hours were needed for setup (filling
the matrix and calculating plane-wave expansion), four hours were required for 41 iterations to reach 0.001
normalized residual error, and two hours were required for calculating 1201 points of bistatic RCS}. A good
agreement between the calculations and the Mie-series solution was observed. The RMS error was 0.30 dB for
all 1201 points for θ varying from 0° to 120°.
A computer code, named FISC (Fast Illinois Solver Code), has been co-developed by the Center for
Computational Electromagnetics, University of Illinois, and DEMACO [13-8]. FISC [13-9] is designed to
compute the RCS of a target described by a triangular-facet file. The problem is formulated using the Method
of Moments (MoM), where the Rao, Wilton, and Glisson basis functions are used. The resultant matrix
equation is solved iteratively by the Conjugate Gradient (CG) method. The Multilevel Fast Multipole
Algorithm (MLFMA) is used to speed up the matrix-vector multiply in the CG method.

Figure 13-1 : The CPU time per iteration and memory requirements (points) as functions of the number of
unknowns for FISC. Two curves, 8x10-5NlogN and 2.7x10-3N, are also plotted for comparison [13-9].
28

Domain decomposition method

The EMC analysis of a complex structure leads, in most cases, to prohibitive computation time and/or
memory requirements. The principle of the proposed method [13-10, to 13-14] is to decompose the complete
problem into a set of smaller problems, which interact only through a limited number of interfaces. In each
sub-domain we solve series of boundary-value problems which completely parametrize the behaviour of the
sub-domain as far as the field relations on the interfaces are concerned. This parametrization can be put in the
form of an interface admittance operator or an interface scattering operator.
This technique has a lot of advantages such as :
• A change in one of the sub-domain necessitates only the recalculation of this particular sub-domain,
• One can use different numerical methods adapted to the particular sub-domain problem.
However, the gain in efficiency is interesting only when the number of unknowns on the interfaces is small
compared to the number of unknowns of the original problem.
Using 3D codes coupled with a transmission line code, this technique has been used with success to predict
electromagnetic coupling on cable bundles located in complex 3D structures [13-15 to 13-20].

Conclusions
Various methods for efficiently solving electromagnetic problems have been described. A fundamental
description of each technique and an overview of the types of problems they are best suited to analyze have
been presented. References have been provided that direct the reader to more detailed information and sources
of computer codes.
The state-of-the-art in numerical modeling is progressing rapidly. Each year new types of problems can be
analyzed. Implementation of these techniques are getting more accurate and powerful.
Computational techniques for solving electromagnetic wave scattering problems involving large complex
bodies and for analyzing wave propagation through inhomogeneous media have been intensely studied by
many researchers in the past. This is due to the importance of this research in many practical applications,
such as the prediction of the Radar Cross Section (RCS) of complex objects like aircrafts, the interaction of
antenna elements with aircraft and ships, the environmental effects of vegetation, clouds, and aerosols on
electromagnetic wave propagation, the interaction of electromagnetic waves with biological media, and the
propagation of signals in high-speed and millimeter-wave circuits. The recent phenomenal growth in
computer technology, coupled with the development of fast algorithms with reduced computational
complexity and memory requirements, have made a rigorous numerical solution of the problem of scattering
from electrically large objects feasible. These numerical techniques involve either solving partial-differential
equations with the Finite-Difference Method (FDM) or the Finite-Element Method (FEM) which result in
sparse matrices, or integral equations which are converted into dense matrix equations using the Method Of
Moments (MOM). To reduce the computational complexity of such computational techniques, especially for
large-scale electromagnetic problems, several powerful solvers have been developed. Among these solvers,
iterative solvers are ubiquitously used to solve both differential and integral equations. Iterative solvers, in
general, require less memory storage, and exhibit reduced computational complexities when compared to
direct solvers. Hence, they portend an important method for large scale computing.
For surface structures, there exists no direct solver with reduced computational for efficiently solving the
integral equation of scattering. Therefore, one resorts to an iterative solver whereby the computational
complexity of a matrix-vector multiply can be reduced. Many methods for expediting matrix-vector multiplies
have been proposed, but the Fast Multipole Method (FMM) and its variants hold most promise in providing a
fast method that applies to scatterers or arbitrary geometry.
Even though a matrix-vector multiply for scattering problems only require O(NlogN) operations both for
volume scattering and surface scattering problems, the number of iterations needed remains unpredictable.
Therefore, preconditioning techniques for reducing the required number of iterations in iterative methods are
urgently needed in solving electromagnetic wave scattering problems. Finally, even though direct solvers with
reduced computational complexities are available for volumetric scattering problems, no such solvers exist for
surface scatterers, except for collinear (or almost coplanar) structures. Hence, this remains an open problem
for researchers in the future.

Bibliography

[2-1] J.A. Landt and E.K. Miller Transient Response of the Infinite Cylindrical Antenna and Scatterer. IEEE
Trans. Antennas Propagat., Vol. AP-24, p. 246, 1976.
 29

[2-2] K.S.Yee Numerical Solution of Initial Boundary Value Problems Involving Maxwell's Equations in
Isotropic Media. IEEE Trans. Antennas Propagat., vol. 14, pp. 302-307, 1966.

[2-3] K.L. Shlager and J.B. Schneider A Selective Survey of the Finite-Difference Time Domain Literature
IEEE Antennas Propagat. Mag. Vol. 37, pp. 39-57, 1995.

[2-4] K.M. Mitzner Numerical Solution for Transient Scattering from a Hard Surface of Arbitrary Shape-
Retarded Potential Technique. J. Acoust. Soc. Am., vol. 42, pp. 391-397, 1967.

[2-5] C.L. Bennett and W.L. Weeks Electromagnetic Pulse Response of Cylindrical Scatterer in 1968 IEEE
G-AP International Symposium, Northeastern University, Boston, pp. 176-183, 1968.

[2-6] C.L. Bennett and W.L. Weeks Transient Scattering from Conducting Cylinders IEEE Trans. Antennas
Propagat. vol. 18, pp. 627-633, 1970.

[2-7] E.P. Sayre and R.F. Harrington Transient Response of Straight Wire Scatterers and Antennas. In 1968
IEEE G-AP International Symposium, Northeastern University, Boston, pp. 160-164, 1968.

[2-8] E.P. Sayre and R.F. Harrington Time Domain Radiation and Scattering by Thin Wires Appl. Sci. Res.,
vol. 26, pp. 413-444, 1972.

[2-9] P.B. Johns and R.L.Beurle Numerical Solution of Two-Dimensional Scattering Problems Using a
Transmission-Line Matrix Proc. IEEE, vol. 118, Pt. H, pp. 1203-1208, 1971.

[2-10] S. Nam, H. Ling and T. Itoh Characterization of Uniform Microstrip Line and Its Discontinuities Using
the Time Domain Method of Lines. IEEE Trans. Microwave Theory Tech., vol. 37, pp. 2051-2057, 1989.

[2-11] T.W. Veruttipong Time Domain Version of the Uniform GTD IEEE Trans. Antennas Propagat., vol. 38,
pp. 1757-1764, 1990.

[2-12] P.O. Brundell Transient Electromagnetic Waves around a Cylindrical Transmitting Antenna, Erricsson
Tech., vol. 16, pp. 137-162, 1960.

[2-13] T.T. Wu Transient Response of a Dipole Antenna J. Math. Phys., vol. 2, pp. 982-984, 1961.

[2-14] O. Einarsson The Step-Voltage Current Response of an Infinite Conducting Cylinder. Trans. R. Inst.
Technol., Stockholm, Sweden, pp. 191, 1962.

[2-15] G. Franceschetti and C.H. Papas Pulsed Antennas IEEE Trans. Antennas Propagat., vol. 22, pp. 651-
661, 1974.

[2-16] A.G. Tijhuis, P. Zhongqiu and A.R. Bretones Transient Excitation of a Straight Thin-Wire Segment: A
New Look at an Old Problem IEEE Trans. Antennas Propagat., vol. 40, pp. 1132-1146, 1992.

[2-17] E.K. Miller, A.J. Poggio and G.J. Burke An Integro-Differential Equation Technique Equation
Technique for the Time Domain Analysis of Thin-Wires Structures Part I- The Numerical Method, Part II-
Numerical Results, J. Comput. Phys., vol. 12, 1973.

[2-18] A.J. Poggio and E.K. Miller Integral Equation Solution of Three-Dimensional Scattering Problems. In
Computer Techniques for Electromagnetics, R. Mittra, ed., Pergamon, New York, 1973.

[2-19] T.K. Lui and K.K. Mei A Time Domain Integral Equation Solution for Linear Antennas and Scatterers.
Radio Sci., vol. 8, pp.797-804, 1973.

[2-20] C.L. Bennett The Numerical Solution of Transient Electromagnetic Scattering Problems In
Electromagnetic Scattering , P.G.E. Uslenghi, ed., Academic Press, New York, pp. 393-428, 1978.
30

[2-21] C.L. Bennett Time Domain Solution via Integral Equation-Surfaces and Composite Bodies. In
Theoretical Methods for Determining the Interaction of Electromagnetic Waves with Structures. Sijthoff and
Noordhoff, Rockville, MD, pp. 255-275, 1981.

[2-22] C.L. Bennett and H. Mieras Time Domain Scattering from Open Thin Conducting Surfaces. Radio Sci.,
vol. 16, pp. 1231-1239, 1981.

[2-23] C.L. Bennett and H. Mieras Space-Time Integral Equation Approach to Dielectric Targets. IEEE
Trans. Antennas Propagat., vol. 30, pp. 2-9, 1982.

[2-24] R. Gomez, J.A. Morente and A. Salinas Time Domain Analysis of an Array of Straight-Wire Coupled
Antennas. IEEE Electronic Lett., vol. 22, pp. 316-318, 1986.

[2-25] E. Marx Electromagnetic Pulse Scattered by a Sphere IEEE Trans. Antennas Propagat., vol. 35, pp.
412-417, 1987.

[2-26] A.R. Bretones, A. Salinas, R. Gomez-Martin and A. Perez The Comparison of a Time Domain
Numerical Code (DOTIG1) with Several Frequency-Domain Codes Applied to the Case of Scattering from a
Thin-Wire Cross ACES J.,pp. 121-129, 1989.

[2-27] R. Gomez, A. Salinas, A.R. Bretones, J. Fornieles and M. Martin Time Domain Integral Equations for
EMP Analysis. Int. J. Numerical Modeling, vol. 4, pp. 153-162, 1991.

[2-28] R. Gomez, A. Salinas, and A.R. Bretones Time Domain Integral Equation Methods for Transient
Analysis. IEEE AP-S Mag., vol. 34, pp. 15-22, 1992.

[2-29] S.M. Rao and D.R. Wilton Transient Scattering by Conducting Surfaces of Arbitrary Shape. IEEE
Trans. Antennas Propagat., vol. 39, pp. 56-61, 1991.

[2-30] D.A. Vechinski and S.M. Rao A Stable Procedure to Calculate the Transient Scattering by Conducting
Surfaces of Arbitrary Shape. IEEE Trans. Antennas Propagat., vol. 40, pp. 661-665, 1992.

[2-31] D.A. Vechinski, S.M. Rao and T.K. Sarkar Transient Scattering from Three-Dimensional Arbitrarily
Shaped Dielectric Bodies. J. Optical Soc. Am., vol. 11, pp. 1458-1470, 1994.

[2-32] S.P. Walker, M.J. Bluck, M.D. Pocock, C.Y. Leung and S.J. Dodson Curvilinear, Isoparametric
Modeling for RCS Prediction Using Time Domain Integral Equation. In 12th Annual Review of Progress in
APPLIED Computational Electromagnetics, vol. 1, pp. 196-204, 1996.

[2-33] S.P. Walker Developement in Time Domain-Equation Modeling at Imperial College. IEEE Trans.
Antennas Propagat., vol. 39, pp. 7-19, 1997.

[2-34] J.A. Landt, E.K. Miller and F.J. Deadrick Time Domain Modeling of Nonlinear Loads IEEE Trans.
Antennas Propagat., vol. 31, pp. 121-126, 1983.

[2-35] T.K. Sarkar and D.D. Weiner Scattering Analysis ol Nonlinearly Loaded Antennas. IEEE Trans.
Antennas Propagat., vol. 24, pp. 125-131, 1976.

[2-36] C.L. Bennett and G.F. Ross Time Domain Electromagnetics and its Applications. Proc. IEEE, vol.
66,pp. 299-318, 1978.

[2-37] E.K. Miller and J.A. Landt Direct Time Domain Techniques for Transient Radiation and Scattering
from Wires Proc. IEEE, vol. 68, pp. 1396-1423, 1980.

[2-38] E.K. Miller An Overview of Time Domain Integral-Equation Models in Electromagnetics. J.

Electromagnetics Waves Appl., vol. 1, pp. 269-293, 1987.
 31

[2-39] E.K. Miller Time Domain Modeling in Electromagnetics. J. Electromagnetics Waves Appl., vol. 8, pp.
1125-1172, 1994.

[2-40] L. Felsen Transient Electromagnetics. Springer-Verlag, New York, 1976.

[2-41] S.M. Rao (ed.) Time Domain Electromagnetics. Academic Press, 1999.

[2-42] E.K. Miller Time Domain Measurements in Electromagnetics. Van Nostrand-Reinhold, New York,
1986.

[2-43] K.S. Kunz and R.J. Luebbers The Finite Difference Time Domain Method in Electromagnetics. CRC
Press, Boca Raton, FL, 1993.

[2-44] A. Taflove Computational Electromagnetics: The Finite-Difference Time Domain Method. Artech
House, Boston, 1995.

[2-45] C. Christopoulos Transmission-Line Modeling (TLM) Method. IEEE Press, Piscataway, NJ, 1995.

[2-46] B. Noël Ultra-Wideband Radar. In Proceedings of the First Los Alamos Symposium, CRC Press, Boca
Raton, FL, 1991.

[2-47] H.L. Bertoni, L. Carin and L.B. Felsen Ultra-Wideband Short-Pulse Electromagnetics. Plenum, New
York, 1993.

[2-48] J.D. Taylor Introduction to Ultra-Wideband Radar Systems. CRC Press, Boca Raton, FL, 1995.

[2-49] D. Lamensdorf and L. Susman Baseband-Pulse-Antenna Techniques IEEE Trans. Antennas Propagat.
Mag., vol. 36, pp. 20-30, 1994.

[3-1] R. Courant Variational Methods for the Solution of Problems of Equilibrium and Vibrations. Bull. Am.
Math. Soc., vol. 49, pp. 1-23, 1943.

[3-2] C.S. Desai and J.F. Abel Introduction to the Finite Element Method: A Numerical Approach for
Engineering Analysis. New York: Van Nostrand Reinhold, 1972.

[3-3] D.R. Lynch and K.D. Paulsen Origin of Vector Parasites in Numerical Maxwell Solutions IEEE Trans.
Microwave Theory and Tech., vol. MTT-39, pp. 383-394, March. 1991.

[3-4] K.D. Paulsen and D.R. Lynch Elimination of Vector Parasites in Finite Element Maxwell Solutions.
IEEE Trans. Microwave Theory and Tech., vol. MTT-39, pp. 395-404, March. 1991.

[3-5] M.N.O. Sadiku A Simple Introduction to Finite Element Analysis of Electromagnetic Problems. IEEE
Trans. Educ., vol. 32, n° 2, pp. 85-93, May 1989.

[3-6] MSC/EMASTM, Finite-Element Software available from MacNeal-Schwendler Corporation, 9076 North
Deerbrook Trail, Milwaukee, WI 53223-2434.

[3-7] MAXWELLTM, Finite-Element Software available from Ansoft Corporation, 4516 Henry Street,
Pittsburgh, PA 15213.

[3-8] G.L. Maile Three-Dimensional Analysis of Electromagnetic Problems by Finite Element Methods. Ph.D.
dissertation, University of Cambridge, Dec. 1979.

[3-9] J.P. Webb Developments in Finite Element Method for Three-Dimensional Electromagnetic Problems.
Ph.D. dissertation, University of Cambridge, Sept. 1981.
32

[3-10] P.P. Silvester and R.L. Ferrari Finite Elements for Electrical Engineers 2nd Ed., Cambridge University
Press, Cambridge, 1990.

[3-11] H. Kardestuncer (ed.) Finite Element Handbook New York: Mc-Graw-Hill, pp. 4191-4207, 1987.

[3-12] W.C. Thacker A Brief Review of Techniques for Generating Irregular Computational Grids. Inter. J.
Num. Meth. Engr., vol. 15, pp. 1335-1341, 1980.

[3-13] E. Hinton and D.R.J. Owen An Introduction to Finite Element Computations. Swansea, UK: Pineridge
Press, pp. 247, 328-346, 1979.

[3-14] M.V.K. Chari and P.P. Silvester (eds.) Finite Elements for Electrical and Magnetic Field Problems.
Chichester: John Wiley, pp. 125-143, 1980.

[3-15] P. Silvester Construction of Triangular Finite Element Universal Matrices. Inter. J. Engr.Sci., vol. 12,
pp. 237-244, 1978.

[3-16] P. Silvester High-Order Polynomial Triangular Finite Elements for Potential Problems. Inter. J.
Engr.Sci., vol. 7, pp. 849-861, 1969.

[3-17] G.O. Stone High-Order Finite Elements for Inhomogeneous Acoustic Guiding Structures. IEEE Trans.
Micro. Theory Tech., vol. MTT-21, n° 8, pp. 538-542, Aug. 1973.

[3-18] A. Konrad High-Order Triangular Finite Elements for Electromagnetic Waves in Anisotropic Media.
IEEE Trans. Micro. Theory Tech., vol. MTT-25, n° 5, pp. 353-360, May 1977.

[3-19] P. Daly Finite Elements for Field Problems in Cylindrical Coordinates. Inter. J. Num. Meth. Engr.,
vol. 6, pp. 169-178, 1973.

[3-20] B.H. McDonald and A. Wexler Finite Elements Solution of Unbounded Field Problems. IEEE Trans.
Micro. Theory Tech., vol. MTT-20, n°12, pp. 841-847, Dec.1972.

[3-21] S. Washisu, et al. Extension of Finite Element Method to Unbounded Field Problems. Elect. Lett., vol.
15, n° 24, pp. 772-774, Nov. 1979.

[3-22] Z.J. Csendes A Note on the Finite Element Solution of Exterior Field Problems. IEEE Trans. Micro.
Theory Tech., vol. MTT-24, n°7, pp. 468-473, July 1976.

[3-23] T. Corzani, et al. Numerical Analysis of Surface Wave Propagation Using Finite and Infinite Elements.
Alta Frequenza, vol. 51, n°3, pp. 127-133, June 1982.

[3-24] O.C. Zienkiewicz, et al. Mapped Infinite Elements for Exterior Wave Problems. Inter. J. Num. Meth.
Engr., vol. 21, 1985.

[3-25] K.H. Lee, et al. A Hybrid Three-Dimensional Electromagnetic Modeling Scheme. Geophys., vol. 46,
n°5, pp. 796-805, May 1981.

[3-26] S.J. Salon and J. Peng Hybrid Finite Element Boundary Element Solutions to Axisymetric Scalar
Potential Problems. In Z.J. Caendes (ed.) Computational Electromagnetics. New York: North-Holland/
Elsevier, pp. 251-261, 1986.

[3-27] M.A. Morgan, et al. Finite Element Boundary Integral Formulation for Electromagnetic Scattering.
Wave Motion, vol. 6, n°1, pp. 91-103, 1984.

[3-28] S. Kagami and I. Fukai Application of Boundary Element Method to Electromagnetic Field Problems.
IEEE Trans. Micro. Theory Tech., vol. MTT-32, n°4, pp. 455-461, Apr. 1984.
 33

[3-29] S. Washiru, et al. An Analysis of Unbounded Field Problems by Finite Element Method. Electr. Comm.
Japan, vol. 64-B, n°1,pp. 60-66, 1981.

[3-30] K.L. Wu and J. Litva Boundary Element Method for Modelling MIC Devices. Elect. Lett., vol. 26, n°8,
pp. 518-520, April 1990.

[3-31] M.N.O. Sadiku and A.F. Peterson A Comparison of Numerical Methods for Computing
Electromagnetic Fields. Proc. of IEEE South-Eastcon, pp. 42-47, April 1990.

[4-1] R.F. Harrington Field Computation by Moment Method. The Macmillan Co., New York, 1968.

[4-2] T.H. Hubing Calculating the Currents Induced on Wires Attached to Opposite Sides of a Thin Plate.
ACES Collection of Canonical Problems, Set 1, published by Applied Computational Electromagnetics
Society, pp. 9-13, Spring 1990.

[4-3] G.J. Burke and A.J. Poggio Numerical Electromagnetic Code (NEC) - Method of Moments. Naval Ocean
Syst. Center, San Diego, CA, NOSC Tech. Document 116, Jan. 1981.

[4-4] Thin Wire Time Domain Code (TWTD), contact G.J. Burke, Lawrence livermore National
Laboratories, Livermore, CA.

[4-5] M.M. Ney Method of Moments as applied to Electromagnetics Problems. IEEE Trans. Micro. Thev.
Tech., vol. MTT-33, n° 10, pp. 972-980, Oct. 1985.

[4-6] J.J. Wang Generalized Moment Methods in Electromagnetics. IEE Proc., vol. 137, Pt. H, n° 2, pp. 127-
132, April 1990.

[4-7] P.M. Morse and H. Feshbach Methods of Theoretical Physics. New York: McGraw-Hill, Part I, Chap. 7,
pp. 791-895, 1953.

[4-8] C.A. Balanis Advanced Engineering Electromagnetics. New York: John Willey, pp. 670-742, 851-916,
1989.

[4-9] E. Butkov Mathematical Physics. New York: Addison-Wesley, pp. 503-552, 1968.

[4-10] J.D. Jackson Classical Electrodynamics. 2nd ed. New York: John Wiley, pp. 119-135, 1975.

[4-11] G. Goertzed and N.Tralli Some Mathematical Methods of Physics. New York: McGraw-Hill, 1960.

[4-12] W.V. Lovitt Linear Integral Equations. New York: Dover Publ., 1950.

[4-13] C.D. Green Integral Equations Methods. New York: Barnes & Nobles, 1969.

[4-14] R.F. Harrington Matrix methods for field problems. Proc. IEEE, vol. 55, n° 2, pp. 136-149, Feb. 1967.

[4-15] R. Mittra (ed.) Computer Techniques for Electromagnetics. Oxford: Pergamon Press, pp. 7-95, 1973.

[4-16] H.J. Strait Applications of the method of moments to electromagnetics. St. Cloud, FL: SCEEE Press,
1980.

[4-17] J. Moore and P. Pizer (eds.) Moment Methods in Electromagnetics: Techniques and Application.
Letchworth, UK: Research Studies Press, 1984.

[4-18] R.M. Bevensee Computer codes for EMP interactions and coupling. IEEE Trans. Ant. Prog., vol. AP-
26, n° 1, pp. 156-165, Jan. 1978.
34

[4-19] G.J. Burke and A.J. Poggio Numerical Electromagnetic Code (NEC)-Method of Moments. Lawrence
Livermore National Lab., Jan. 1981.

[4-20] J.W. Rockway, et al. The MININEC System: Microcomputer Analysis of Wire Antennas. Norwood,
MA: Artech House, 1988.

[4-21] R.F. Harrington et al. (eds) Lectures on Computational Methods in Electromagnetics. St. Cloud, FL:
SCEEE Press, 1981.

[4-22] R. Mittra (ed.) Numerical and Asymptotic Techniques in Electromagnetics. New York: Springer-
Verlag, 1975.

[4-23] G.L. James Geometrical Theory of Diffraction for Electromagnetic Waves. 3rd ed. London: Peregrinus,
1986.

[5-1] K.S. Yee Numerical Solution of Initial Boundary Value Problems Involving Maxwell's Equations in
Isotropic Media. IEEE Trans. on Antennas and Propagat., vol. AP-14, pp. 302-307, May 1966.

[5-2] J.S. Shang A Fractional Step Method for Solving 3D Time-Domain Maxwell Equations. J. Comp.
Phys., vol. 118, pp. 109-219, 1995.

[5-3] J.S. Shang and R.H. Fitten A Comparative Study of Characteristic-Based Algorithms for the Maxwell
Equations. J. Comp. Phys., vol. 125, pp. 378-394, 1996.

[5-4] J.S. Shang Characteristic-Based Algorithms for Solving the Maxwell Equations in the Time Domain.
IEEE Antennas and Propagation Magazine, vol. 37, pp. 15-25 , June 1995.

[5-5] R. Courant, E. Isaacson, and M. Reeves On the Solution of Nonlinear Hyperbolic Differential Equations
by Finite Differences. Comm. on Pure and Appl. Math., vol. 5, pp. 243-255, 1952.

[5-6] V. Shankar and W.F. Hall A Time Domain Differential Solver for Electromagnetic Scattering. URSI
Meeting., Univ. of Colorado, Boulder, CO, January 1988.

[5-7] A. Taflove and K.R. Umashankar Finite Difference Time Domain Method. Electromagnetics, vol. 10,
pp. 105-126, 1990.

[5-8] J.P. Berenger Perfectly Matched Layer for the FDTD Solution of Wave-Structure Interaction Problems.
IEEE Trans. on Antennas and Propagat., vol. 44, pp. 110-117 , January 1996.

[5-9] J.P. Berenger A Perfectly Matched Layer for the Absorption of Electromagnetic Waves. J. Comput.
Phys., vol. 114, pp. 185-200, 1994.

[5-10] J.P. Berenger Three-Dimensional Perfectly Matched Layer for the Absorption of Electromagnetic
Waves. J. Comput. Phys., vol. 127, pp. 363-379, 1996.

[5-11] J.R. Wait On the PML Concept: A View from the Outside. IEEE Antennas and Propagation Magazine,
vol. 38, pp. 48-51, April 1996.

[5-12] Z. Wu and J. Fang Numerical Implementation and Performance of Perfectly Matched Layer Boundary
Condition for Waveguide Structures. IEEE Trans. on Microwave Theory and Techn., vol. 43, pp. 2676-2683,
Dec. 1995.

[5-13] W.C. Chew and J.M. Jin Perfectly Matched Layers in the discretized space: an analysis and
optimization. Electromagnetics, vol. 16, pp. 325-340, 1996.

[5-14] J.W. Nehrbass, J.F. Lee and R. Lee Stability Analysis for Perfectly Matched Layered Absorbers.
Electromagnetics, vol. 16, pp. 385-397, 1996.
 35

[5-15] D.C. Wittwer and R. W. Ziolkowski How to Design the Imperfect Berenger PML Electromagnetics,
vol. 16, pp. 465-485, 1996.

[5-16] D.J. Riley and C.D. Turner Local Tetrahedron Modeling of Microelectronics Using the Finite-Volume
Hybrid-Grid Technique. SANDIA Report n° SAND95-2790, UC-706, December 1995.

[5-17] N.K. Madsen and R.W. Ziolkowski Numerical Solutions of Maxwell’s Equations in the Time-Domain
Using Irregular Nonorthogonal Grids. Waves Motion, vol. 10, pp. 538-596, 1988.

[5-18] A.H. Mohammadian, V. Shankar, and W.F. Hall Computation of electromagnetic Scattering and
Radiation Using a Time-Domain Finite-Volume Discretization Procedure. Comput. Phys. Commun., vol. 68,
pp. 175-196, 1991.

[5-19] P. Bonnet, et al. Numerical Modeling of Scattering Problems Using a Time-Domain Finite-Volume
Method. J. Electromag. Waves Appl., vol.11, pp. 1165-1189, 1997.

[5-20] P. Bonnet, et al. Electromagnetic Wave Diffraction Using a Finite Volume Method Electronics Letters,
vol. 33, n° 1, pp.107-108, Jan. 1997.

[5-21] X. Ferrieres and J.C. Alliot Finite Volume Method to Solve Electromagnetic Diffraction Problems.
Proceedings of the 1999 ICOLSE , Toulouse, June 22-24, 1999.

[5-22] K.S. Yee and J.S. Chen The Finite-Difference Time-Domain (FDTD) and the Finite-Volume Time-
Domain (FVTD) Methods in Solving Maxwell’s Equations. IEEE Trans. Antennas Propagat., vol. 45, pp. 354-
363, 1997.

[5-23] J.P. Cioni and M. Remaki Comparaison de deux Méthodes de Volumes Finis en Electromagnétisme.
Rapport de Recherche INRIA, n° 3166, May 1997.

[5-24] J.P. Cioni, L. Fezoui, and D. Issautier High Order Upwind Schemes for Solving Time-Domain
Maxwell’s Equations. La Recherche Aérospatiale, n° 5, 1994.

[5-25] M. Remaki, L. Fezoui and F. Poupaud Un nouveau schéma de type volumes finis appliqué aux
équations de Maxwell en milieu hétérogène. Rapport de recherche INRIA, n° 3351, January 1998.

[5-26] M.A. Jensen and Y. Rahmat-Samii Finite Difference and Finite Volume Time Domain Techniques in
Electromagnetics: A Comparative Study. Radio Science, vol. 31, pp. 1823-1836, November-December 1996.

[5-27] N.K. Madsen and R.W. Ziolkowski A Three-Dimensionnal Modified Finite Volume Technique for
Maxwell's Equations. Electromagnetics, vol. 10, pp. 147-161, 1990.

[5-28] R. Le Martret and C. Le Potier Finite-Volume Solution of Maxwell's Equations in Nonsteady Mode.
La Recherche Aérospatiale, n° 5, pp. 329-342, 1994.

[5-29] K.S. Yee and J.S. Chen Impedance Boundary Condition Simulation in the FDTD/FVTD Hybrid. IEEE
Trans. on Antennas and Propagat., vol. 45, pp. 921-925, June 1997.

[5-30] J.Grando, G. Labaune, J.C. Alliot, and Francois Issac Comparison of Experimental and Numerical
Results for Transient Electromagnetic Fields induced on a Scale Model Aircraft by Current Injection
Technique. IEEE Antennas and Propagat. Soc. Int Symposium, vol. 4, (San Jose, CA), 1989.

[5-31] J.C. Alliot, J.Grando, and X.Ferrières A 3D Finite Difference Solution of the External and Internal
Responses of an Aircraft during in-flight Lightning Strikes. EMC Symposium, Zurich (Switzerland) 1991.

[5-32] X.Ferrières, J.Grando, and J.C. Alliot Using Time Domain Methods (FDTD, MOT) for Radar Cross
Section (RCS) Predictions on Perfectly Conducting Objects. Approximations and Numerical Methods for the
Solution of Maxwell’s Equations. Oxford, 1995.
36

[5-33] J.Grando, X.Ferrières, P.Levesque, F. Issac, and J.C. Alliot FDTD Application to the Electrical
Characterization of Materials by Solving an Inverse Problem. IEEE Antennas and Propagat. Soc. Int
Symposium, vol. 3, ( Montreal Canada), 1997.

[5-34] P. Bonnet, et al. Numerical Modeling of Scattering Problems Using a Time-Domain Finite-Volume
Method. Journal of Electromagnetic Waves and Applications, vol. 11, pp. 1165-1189, 1997.

[5-35] J. Grando, B. Michelsen, F.Issac, and J.C. Alliot FDTD Formalism Including a Micro-Strip Inside an
Elementary Cell. IEEE Antennas and Propagat. Soc. Int Symposium, vol 1, (Atlanta, Georgia), 1998.

[5-36] G. Franceschetti Fundamentals of Steady-State and Transient Electromagnetic Fields in Shielding

Enclosures. IEEE Trans. Electromagnetic Compat., vol. EMC-21, pp. 335-348, November 1979.

[5-37] A.T. de Hoop The N-Port Receiving Antenna and its Equivalent Electrical Network. Philips Res.
Repts., vol. 30, pp. 302-315, 1975.

[5-38] A. Panayiotis, A. Tirkas and C.A. Balanis Finite-Difference Time-Domain Method for Antenna
Radiation. IEEE Trans. Antennas Propagat., vol. AP-40, pp. 334-340, March 1992.

[5-39] F. Hermeline Two Coupled Particle-Finite Volume Methods Using Delaunay-Voronoi Meshes for the
Approximation of Vlasov-Poisson and Vlasov-Maxwell Equations. J. Comp. Phys., vol. 106, pp. 1-18, 1993.

[5-40] D. Issautier, F. Poupaud, J.P. Cioni, and L. Fezoui A 2D Vlasov-Maxwell Solver on Unstructured
Meshes. Waves 95 , Mathematical and Numerical Aspects of Wave Propagation, Mandelieu-La Napoule, pp.
355--371, 1995.

[5-41] V. Gobin, J.P. Aparicio, J. Grando and J.C. Alliot The Surface Impedance: a Pertinent Parameter to
Describe Finite Conductivity Materials in Numerical Codes. EMC Symposium, Zurich (Switzerland), March
12-14, 1991.

[5-42] V. Gobin, F. Issac and F. Jaillot Modeling of Electrically Thick Materials : Theoretical and
Experimental Aspects. ICOLSE 91, Cocoa Beach, FL (USA), April 16-19, 1991.

[5-43] R. Holland and L. Simpson Finite Difference Analysis of EMP Coupling to Thin Struts and Wires.
IEEE Trans. Electromagnetic Compat., vol. EMC-23, pp. 88-97, May 1981.

[5-44] J.Grando, F.Issac, G.Labaune, J.C. Alliot, and X. Ferrières Field Penetration Through Composite
Material Using FDTD Method. IEEE Antennas and Propagat. Soc. Int Symposium, vol. 4, (Dallas,TX), 1990.

[5-45] J. Grando, F. Issac, X. Ferrières, and J.C. Alliot FDTD Method for Electromagnetic Coupling Through
Composite Material with Contact Resistance. IEEE Antennas and Propagat. Soc. Int Symposium, vol. 3,
(London,Ontario ), 1991.

[5-46] J. Grando, F. Issac, M. Lemistre, and J .C. Alliot Stability Analysis Including Wires of Arbitrary Radius
in FDTD Code. IEEE Antennas and Propagat. Soc. Int Symposium, vol. 1, (Ann Arbor, MI), 1993.

[5-47] P. Bonnet, X.Ferrières, J.Grando, and J.C. Alliot FVTD Applied to Dielectric or Wire Structures. IEEE
Antennas and Propagat. Soc. Int Symposium, vol. 1, Baltimore, 1996.

[5-48] P. Bonnet, X. Ferrières, J. Grando, and J.C. Alliot Frequency-Domain Finite Volume Method for
Electromagnetic Scattering. IEEE Antennas and Propagat. Soc. Int Symposium, vol 1, (Atlanta, Georgia),
1998.

[5-49] D. Kalfon and P. Harran-Klotz A Hybrid Finite Difference - Finite Volume Method for Solving
Maxwell Equations in Time Domain. URSI Meeting, Newport Beach, CA, June 1995.
 37

[5-50] D. Kalfon, P. Harran-Klotz and D. Volpert Mixed Methods for Solving Maxwell Equations. Workshop
on Approximations and Numerical Methods for the Solution of the Maxwell Equations, Oxford University,
Oxford , March 1995.

[5-51] A. Wexler Computation of Electromagnetic Fields. IEEE Trans. Micro. Theo. Tech., vol. MTT-17, n°
8, pp. 416-439, Aug. 1969.

[5-52] B.P. Rynne Instabilities in Time Marching Methods for Scattering Problems. Electromagnetics, vol. 6,
n° 2, pp. 129-144, 1986.

[5-53] J.I. Steger and R.F. Warming On the Convergence of Certain Finite-Difference Schemes by an
Inverse-Matrix Method. J. Comp. Phys., vol. 17, pp. 103-121, 1975.

[5-54] D.W. Kelly, et al. A Posteriori Error Estimates in Finite Difference Techniques. J. Comp. Phys., vol.
74, pp. 214-232, 1988.

[6-1] GEMACS, software available from Advanced Electromagnetics, 5617 Palomino Dr. NW, Albuquerque,
NM 87120.

[7-1] R.H. Park Definition of an Ideal Synchronoud Machine and Formulators for Armature Flux Linkages.
Gen. Elect. Rev., vol. 31, pp. 332-334, 1928.

[7-2] G. Kron
Equivalent Circuit of the Field Equations of Maxwell.
Proc. IRE, pp. 289-299, May 1944.

[7-3] G. Kron Equivalent Circuits of Electrical Machinery. New York: John Wiley, 1951.

[7-4] N. Marcovitz and J. Schwinger On the Reproduction of the Electric and Magnetic Fields Produced by
Currents and Discontinuity in Wave Guides. J. Appl. Phys., vol. 22, n° 6, pp. 806-819, June 1951.

[7-5] J. Schwinger and D.S. Saxon Discontinuities in Waveguides. New York: Gordon and Breach, 1968.

[7-6] P.B. Johns and R.L. Beurle Numerical Solution of 3-Dimensional Scattering Problems Using a
Transmission Line Matrix. Proc. IEEE, vol. 118, n° 9, pp.1203-1208, Sept. 1971.

[7-7] P.B. Johns A Symmetrical Condensed Node for the TLM Method. IEEE Trans. Microwave Theory and
Tech., vol. MTT-35, pp. 370-377, Apr. 1987.

[7-8] W.J.R. Hoefer The Transmission-Line Matrix Method :Theory and Applications. IEEE Trans.
Microwave Theory Tech., vol. MTT-33, n° 10, pp. 882-893, Oct. 1985.

[7-9] N. Yoshida, et al. Transient Analysis of Two-Dimensional Maxwell’s Equations by Bergeron’s Method.
Trans. IECE (Japan), vol. J62B, pp. 511-518, June 1979.

[7-10] D.A. Al-Mukhtar and T.E. Sitch Transmission-Line Matrix Method with Irregularly Graded Space.
IEE Proc., vol. 128, Pt. H, n° 6, pp. 299-305, Dec. 1981.

[7-11] P.B. Johns On the Relationship between TLM and Finite-Difference Methods for Maxwell’s Equations.
IEEE Trans. Micro. Theo. Tech., vol. MTT-35, n° 1, pp. 60-61, Jan. 1987.

[7-12] S. Akhtarzad Analysis of Lossy Microwave and Microstrip Resonators by the TLM Method. Ph.D.
dissertation, University of Nottingham, England, July 1975.

[7-13] W.J.R. Hoefer The Electromagnetic Wave Simulator: A Dynamic Visual Electromagnetic Laboratory
Based on the Two-Dimensional TLM Method. John Wiley & Sons, West Sussex, England, 1991.
38

[8-1] M.F. Iskander, A. Lakhtakia, and C.H. Durney A New Iterative Procedure to Solve for Scattering and
Absorption by Dielectric Objects. Proc. IEEE, vol. 70, N° 11, Nov.1982.

[8-2] Y. Leviatan and A. Boag Analysis of Electromagnetic Scattering from Dielectric Cylinders Using a
Multifilament Current Model. IEEE Trans. Antennas Prop., vol. AP-35, pp. 1119-1127, Oct. 1987.

[8-3] Y. Leviatan, P.G. Li, A.J. Adam, and J. Perini Single-Post Inductive Obstacle in Rectangular
Waveguide. IEEE Trans. Microwave Theory and Tech., vol. MTT-31, pp. 806-812, Oct. 1983.

[8-4] M. Nishimura, S. Takamatsu, and H. Shigescwa A Numerical Analysis of Electromagnetic Scattering of

a Perfect Cylinder by Means of Discrete Singularity Method Improved by Optimization Process. Inst. Elec.
Comm. (Japan), vol. 67-B, N° 5, May 1984.

[8-5] A.C. Ludwig A Comparison of Spherical Wave Boundary Value Matching Versus Integral Equation
Scattering Solutions for a Perfect Conducting Body. IEEE Trans. Antennas Prop., vol. AP-34, N° 7, July
1986.

[8-6] P. Leuchtmann and L. Bomholt Thin wire Features for the MMP-Code. Proc. 6th Annual Rev. of
Progress in Applied Computational Electromagnetics, pp. 233-240, March 1990.

[8-7] P. Leuchtmann New Expansion Functions for Long Structures in the MMP-Code. Proc. 7th Annual Rev.
of Progress in Applied Computational Electromagnetics, pp. 198-202, March 1991.

[8-8] J. Zheng A New Expansion Function of GMT: The Ringpole. Proc. 7th Annual Rev. of Progress in
Applied Computational Electromagnetics, pp. 170-173, March 1991.

[8-9] Artech House Inc., 685 Canton Street, Norwood, MA 02062.

[8-10] C. Hafner The Generalized Multipole Technique for Computational Electromagnetics. Artech House,
Boston, 1990.

[9-1] T.K. Sarkar The Conjugate Gradient Method as Applied to Electromagnetic Field Problems. IEEE
Antennas and Prop. Soc. Newsletter, , vol. 28, pp. 5-14, August 1986.

[9-2] T.K. Sarkar From "Reaction Concept" to "Conjugate Gradient": Have We Made Any Progress?. IEEE
Antennas and Prop. Soc. Newsletter, , vol. 31, pp. 6-12, August 1989.

[10-1] G.J. Burke and A.J. Poggio Numerical Electromagnetic Code (NEC) - Method of Moments. Naval
Ocean Syst. Center, San Diego, CA, NOSC Tech. Document 116, Jan. 1981.

[10-2] MiniNEC, Software available through Artech House Publishers, 685 Canton Street, Norwood, MA
02062.

[10-3] E.H. Newman and D.M. Pozar Electromagnetic Modeling of Composite Wire and Surface Geometries.
IEEE Trans. Antennas Prop., vol. AP-26, pp. 784-789, Nov. 1978.

[10-4] D.R. Wilton and S.U. Hwu Junction Code User's Manual. Naval Ocean Syst. Center, San Diego, CA,
NOSC Tech. Document 1324, Aug. 1988.

[11-1] H. Ling , R.C. Chou and S.W. Lee Shooting and Bouncing Rays : Calculating the RCS of an Arbitrary
Shaped Conductor. IEEE Trans. Antennas and Propagat., vol. 37, pp. 194-205, 1989.

[11-2] Basic Scattering Code (BSC), software available from The Ohio State University ElectroScience
Laboratory, Columbus, OH 43212.

[11-3] C.C. Lu and W.C. Chew Fast Far Field Approximation for Calculating the RCS of Large Objects
ACES Conference Digest, March 1995.
 39

[12-1] A. Taflove and K. Umashankar A Hybrid Moment Method/Finite-Difference Time-Domain Approach

to Electromagnetic Coupling and Aperture Penetration into Complex Geometries. IEEE Trans. Antennas
Prop., vol. AP-30, pp. 617-627, July 1982.

[12-2] M.A. Morgan, C.H. Chen, S.C. Hill, and P.W. Barber Finite Element-Boundary Integral Formulation
for Electromagnetic Scattering Wave Motion, vol. 6, pp. 91-103, 1984.

[12-3] D.R. Lynch, K.D. Paulsen, and J.W. Strohbehn Finite Element Solution of Maxwell's Equations for
Hyperthermia Treatement Planning. J. Comput. Phys., vol. 58, pp. 246-269, 1985.

[12-4] K.D. Paulsen ,D.R. Lynch, and J.W. Strohbehn Three-Dimensional Finite, Boundary, and Hybrid
Elements Solutions of the Maxwell Equations for Lossy Dielectric Media. IEEE Trans. Microwave Theory
and Tech., vol. MTT-36, pp. 682-693, April. 1988.

[12-5] J. Stroka, H. Baggenstos, and R. Ballisti On the Coupling of the Generalized Multipole Technique with
the Finite Element Method. IEEE Trans. on Magnetics, vol. 26, pp. 658-661, March 1990.

[12-6] X.C. Yuan, D.R. Lynch, and J.W. Strohbehn Coupling of Finite Element and Moment Methods for
Electromagnetic Scattering from Inhomogeneous Objects. IEEE Trans. Antennas Prop., vol. 38, pp. 386-393,
March 1990.

[12-7] X.C. Yuan Three-Dimensional Electromagnetic Scattering from Inhomogeneous Objects by the
Hybrid Moment and Finite Element Method. IEEE Trans. Microwave Theory and Tech., vol. 38, N° 8, pp.
1053-1058, Aug. 1990.

[12-8] J.M. Jin and J.N. Volakis A Finite Element-Boundary Integral Formulation for Scattering by Three-
Dimensional Cavity-Backed Apertures. IEEE Trans. Antennas Prop., vol. AP-39, pp. 97-104, January 1991.

[12-9] W.E. Boyse and A.A. Seidl A Hybrid Finite Element and Moment Method for Electromagnetic
Scattering from Inhomogeneous Objects. Proc. 7th Annual Rev. of Progress in Applied Computational
Electromagnetics, pp. 160-169, March 1991.

[12-10] X.C. Yuan, D.R. Lynch, and K.D. Paulsen Importance of Normal Field Continuity in Inhomogeneous
Scattering Calculations. IEEE Trans. Microwave Theory and Tech., vol. 39, pp. 638-642, April 1991.

[13-1] V. Rokhlin Rapid Solution of Integral Equations of Scattering Theory in Two Dimensions. J. Comput.
Phys., vol. 86, n° 2, pp. 414-439, Feb. 1990.

[13-2] R. Coifman, V. Rokhlin, and S. Wandzura The Fast Multipole Method for the Wave Equation : A
Pedestrian Prescription. IEEE Antennas Propagat. Mag., vol. 35, n° 3, pp. 7-12, June 1993.

[13-3] C.C. Lu and W.C. Chew A Fast Algorithm for Solving Hybrid Integral Equation. IEE Proceedings-H,
vol. 140, n° 6, pp. 455-460, Dec. 1993.

[13-4] B. Dembart and E. Yip A 3D Moment Method Code Based on Fast Multipole. Digest of the 1994 URSI
Radio Science Meeting, p. 23, Seattle, Washington, June 1994.

[13-5] R.L. Wagner and W.C. Chew A Ray-Propagation Fast Multipole Algorithm. Micro. Opt. Tech. Lett.,
vol. 7, n° 10, pp. 435-438, July 1994.

[13-6] J.M. Song and W.C. Chew Fast Multipole Method Solution Using Parametric Geometry. Micro. Opt.
Tech. Lett., vol. 7, n° 16, pp. 760-765, Nov. 1994.

[13-7] W.C. Chew, J.M. Jin, C.C. Lu, E. Michielssen and J.M. Song Fast Solution Methods in
Electromagnetics. IEEE Trans. Antennas Propag., vol. 45, n° 3, pp. 533-543, March 1997.
40

[13-8] User’s Manual for FISC (Fast Illinois Solver Code), Center for Computational Electromagnetics,
University of Illinois at Urbana-Champaign and DEMACO, Inc., Champaign, Illinois, January 1997.

[13-9] J.M. Song, C.C. Lu, W.C. Chew, and S.W. Lee Fast Illinois Solver Code (FISC). IEEE Antennas
Propagat. Mag., vol. 40, n° 3, pp. 27-34, June 1998.

[13-10] V. Gobin and S. Bertuol Application à la CEM d’une méthode de découpage en domaines. 9ème
Colloque International de Compatibilité Electromagnétique, Brest, 8-11 Juin 1998.

[13-11] D. Lacour Etude du couplage d’une onde électromagnétique sur une structure complexe par
décomposition en sous-domaines. Thèse de Doctorat de l’Université Paris XI, 25 Juin 1999.

[13-12] D. Lacour, V. Gobin and X. Ferrieres Domain Decomposition Method Applied to the Optimisation of
Cable Routing in Large Structures. PIERS, Cambridge, Massachusetts, USA, July 7-11 1997.

[13-13] D. Lacour, X. Ferrieres , P. Bonnet, V. Gobin and J.C. Alliot Application of a Multi-Domain
Decomposition Method to Solve EMC Problems on an Aeroplane. Electronics Letters, vol. 33, n° 23, pp.
1913-1996, Nov. 1997.

[13-14] D. Lacour, X. Ferrieres , and J.C. Alliot Utilisation de la méthode de décomposition par domaines
dans le domaine temporel. 9ème Colloque International de Compatibilité Electromagnétique, Brest, 8-11Juin
1998.

[13-15] L. Paletta Démarche topologique pour l’étude des couplages électromagnétiques sur des systèmes de
câblages industriels de grande dimension. Thèse de Doctorat de l’Université Paris XI, 28 Sept. 1998.

[13-16] J.P. Parmantier et al. Modeling and Analysis of the Electromagnetic Environment on Aircraft and
Helicopter. Part 2 : Coupling to Complex Cable Networks. Proceedings of the 1999 ICOLSE , Toulouse, June
22-24, 1999.

[13-17] J.P. Parmantier Etude du couplage électromagnétique sur des systèmes de faisceaux de câbles
multiconducteurs complexes jusqu’à 1 GHz. RTS ONERA 17/6727PY , Mai 1997.

[13-18] J.P. Parmantier and P. Degauque Topology Based Modeling of Very Large Systems. Modern Radio
Science 1996, Edité par J. Hamelin, Oxford University Press, pp. 151-177, 1996.

[13-19] J.P. Parmantier et al. An Application of the Electromagnetic Topology Theory on the Test-bed Aircraft
EMPTAC. Interaction Notes, Note n° 506, Nov. 1993.

[13-20] J.P. Parmantier et al. ETE III : Application of Electromagnetic Topology on EMPTAC. Interaction
Notes, Note n° 527, May 1997.
 41

2.3 Test Techniques and Present Limitations

EMC Test on aircraft shall be conducted to verify that the overall system is electromagnetically compatible
among all subsystems and equipment within the system and with environments caused by electromagnetic
effects external to the system. Moreover margins shall be provided based upon system operational
performance requirements, tolerance in system hardware and measurements uncertainties. The paper describes
the test facilities utilized to perform conducted and radiated system tests generating potential internal and
external electromagnetic disturbances and determining safety margins.

INTRODUCTION

An all electric aircraft could have remarkable benefits in terms of weight and maintenance costs with respect
to aircraft that use hydraulic and pneumatic controls; however they present major concern about potential
susceptibility problem of its electronics controls to conducted and radiated electromagnetic signals. In testing
modern aircraft a major objective is aimed to developing techniques and tests methods for assessing the
survivability in the electromagnetic environment of externally generated high intensity radiated field (HIRF)
and internally generated radiated or conducted emissions.
System level tests are conducted with the cause-effects technique. A cause generated by an emissive source
produces an effects which properly monitored allows to define whether a susceptibility exists. In EMC system
definition it’s necessary to establish:
modes of operation
activation of internal and external emissive sources
monitoring methods and techniques

The most common approach is to monitor subsystem performance through visual and aural displays and
outputs because it is usually undesirable to modify cable and electronics to monitor signals. However this
approach in not quite acceptable because it does not generally allow to determine safety margins which are
essential for safety critical subsystems. In addition to taking into account tolerance in system hardware and
uncertainties involved in verification of system level design requirements safety margin demonstration is
necessary to guarantee system performances with regard to system hardware variabilities due to yield spread
and system aging.

SAFETY MARGIN

Suitable monitoring methods shall be adopted to detect system malfunctions following the activation
interference sources. Several issues shall be taken into account:
the use of suitable measuring instrumentation which do not alter the value of parameter under examination
and at the same time are not affected by the interference generated by the emissive sources
the selection of parameters to be monitored which are meaningful of system performances and can be
measured in a quantitative manner
the definition of the detection criteria capable of discriminating the variation of the parameter under test due to
interference source from those ones produced by thermal or environmental effects
The last issue is covered by the safety margin interpretation.
Three different safety margins can be identify with the understanding that they imply specific test methods:
Comparison Safety Margin (CSM)
EMC Safety Margin (ESM)
Performance Safety Margin (PSM)

CSM:
The CSM, as the name implies, is based upon the possibility of exploiting the similarity between equipment
and system tests. If in system tests the emission test signal of amplitude d is measured and is comparable with
the susceptibility equipment test signal s the CSM is expressed as s/d. The term “comparable” implies the
same electrical characteristic of the signals and the same coupling paths.
42

ESM:

d1… dr dR…
…
n1
+ M1
x1 z1 y1
nn
xm + Mn
Z .zp Y yn
nN
+ MN
xM zP yN

i1 … iq … iQ …

Fig.1

MIL-STD-464 (18 March 1997) specifically requires this type of comparison. In that document it is stated that
“past experience has shown that equipment compliance with its EMI requirements assures a high degree of
achieving system level compatibility. No conformance to EMI requirements often leads to system problems”.
In the same document it is noticed that the “D” revision of MIL-STD-461 and MIL-STD-462 emphasize
testing techniques which are more directly related to measurable system level parameters. For instance bulk
cable testing is being implemented for both damped sine transient waveform and modulated continuous wave.
It is stated that the “measured data from these tests can be directly compared to stresses introduced by system
level threats. This philosophy greatly enhances the value of the results and allow for acceptance limits which
have credibility”.
The following test amplitudes at system and equipment level are comparable:
the disturbance at the power supply input terminals of the equipment installed in the system and the
susceptibility signal injected at the same terminals at equipment level
the common mode system conducted emission measured on a cable bundle and the common mode equipment
conducted susceptibility signal injected on the same cable bundle.
When the similarity between the coupling mechanisms at equipment and system level does not exist the CSM
test method cannot be used without making large error.
A typical situation exist when comparing radiated susceptibility equipment tests with radiated emission
system tests. The test environments are completely different and therefore it becomes impossible to make any
comparison.

In Fig.1 the block diagram of a complex aircraft system is shown. The block Z represents the interface to the
external world identified by the parameters x=[x1……xM]T detected and measured by on board sensors
(aircraft position and altitude, speed, positions of targets and threats and so on). The input data are processed
by the aircraft systems as internal parameters z=[z1……zP]T available only from the on board computers and
as
external parameters y=[y1……yN]T corrupted by noise n=[n1……nN]T available to the pilot and presented on
various cockpit displays and monitors. In system immunity tests the susceptibility signals i=[i1……iQ]
(internal environment) and d=[d1……dR] (external environment) define the radiated and conducted
electromagnetic environment required to asses the aircraft vulnerability. They may be generated by external
transmitters, on board transmitters, by the activation of on board emissive devices which can operate
continuously or in transient conditions. Susceptibility signals may be time dependent, in any case they are
deterministic. The repeatability of immunity tests depends on the repeatability of the electromagnetic
environments where the aircraft is tested.
The following system transfer function can be identified:

z=H(x, d, i)
y=G(x, d,i)
 43

The reference test conditions are achieved where the external interference sources are at the minimum level
(environment level dmin) and the internal sources are at the minimum levels (minimum number of operative
equipment imin):

zmin=H(x, dmin, imin)

ymin=G(x, dmin, imin)

Assuming that external interference can be artificially changed until the system tolerance interval extreme a
(b) of z (y) is achieved:

a=H(x, da, imin); b=G(x, db, imin)

we can state that ESM is da/dmin (db/dmin).

This test method is not always applicable because of the electrical and physical constraints of the system.
Typically the ESM is measured in the following way: the conducted interference on cable bundles connecting
the equipment to the system are measured (dmin) and reinjected with a value corresponding to da (db). Basically
the ESM is a safety margin which we can determine by performing susceptibility tests at system level; this
approach is not always possible because there is the risk of upsetting the system in an unrealistic manner.

PSM
The PSM specifies the most meaningful test method because aims at the verification of the actual system
performances. In the past system susceptibilities were monitored on the display M1……MN (Fig.1); the pilot
has the task of establishing the presence of a susceptibility on the basis of a purely subjective evaluation. With
the advent of more integrated system completely controlled by on board computers it becomes possible to
measure the output parameters:

z=H(x, d, i); y=G(x, d, i)

The PSM can be determinated by means of two techniques.:

desensitization: it consists in changing the transfer function H(G) making the system more sensitive to the
wanted signal:

za=Ha(x, d, i); ya=Ga(x, d, i)

in the test of EEDs (Electroexplosive devices) the actual EEDs are substituted by more sensitive devices
capable of detecting signals 20 dB lower than the nominal no fire level
minimum S/N: it consists in reducing the input signal x in order to make the equipment (typically a receiver)
operate at the minimum S/N level.

z’a=H(xmin, d, i); y’a=G(xmin, d, i)

MONITORING TECHNIQUES

As it has been said safety margins imply specific practical monitoring techniques. In the following the most
commonly used ones are described

2.3.1 Electro-Explosive Devices (EEDs)

Radiofrequency fields can induce currents in the electrical cables of the EEDs. Since such currents can
produce the EED activation it is important to determinate their magnitudes even at very high frequencies by
measuring the temperature rise of the EED bridgewire corresponding to the Joule heating. The method, which
is currently used nowadays, is based upon the Fluoroptic Thermometry sensor .

The sensor in the Fluoroptic Thermometry sensor is a photo-luminescent material (phosphor) whose afterglow
varies with temperature. More specifically the time constant of the exponentially decaying fluorescence
44

following pulsed excitation by a flash lamp decreases with increasing temperature. The phosphor, which can
be coated directly onto the bridgewire, is coupled optically with both the exciting source and a photo-detector
by a single optical fiber. The rate of decay of the fluorescence is determined by monitoring the signal from
the photo-detector. The decay time is then converted to temperature by reference to a digital look-up table.
Since both the sensing and data communication are optical, no extraneous electrical conductors are required in
the system under test or in the surrounding high field environment.
There are two basic methods for measuring surface temperatures of a solid, namely the contact and the non
contact methods. The contact method involves the use of a fiberoptic probe with the luminescent sensor
powder dispersed in an optically clear binder attached to the end of the optical fiber. The probe tip is placed in
contact with the surface to be measured. The non contact method requires that the surface of interests be
coated with the phosphor powder/binder mixture and that an open ended optical fiber be used with or without
the aid of a lens or special fiber tip tapering to couple the phosphor optically to an instrument located some
distance away. There are two important advantages of the non contact method over the contact method for the
measurements of low level induced currents via resistive heating:
it eliminates the heat sinking effect (thermal loading) due to the optical fiber since only the phosphor sensing
layer is attached to the resistive conductor
it makes the alignment of the fiber tip with the typically small conductor much easier to achieve
The proposed measuring equipment is Model 790 Fluoroptic Thermomether by Luxtron. One disadvantage of
this type of measuring system is the low response time of sensor which is about 250ms.
One alternative system utilized another technique named Coloroptic (TM by Metricor); light supplied to the
sensor from a LED source is modified at the sensor tip and reflected back along
the same fiber to a detector. The color or spectral makeup of the reflected light is modified in proportion to the
parameter being measured i.e. temperature or current. The instrument then electro-optically translates the data
and displays it. The proposed measuring equipment is Model 1420 EMC Test System by Metricor. With this
equipment it is possible to achieve a better response time which is in range of less than 10ms. The main
disadvantages of this system is that the EED bridgewires shall be substituted by a proper sensor device, while
in the previous method the actual EED bridgewire is used.
The final decision of the system utilize will be based upon the actual characteristics of the chosen EED, which
shall be characterized as specified in [3] according to:
Method 2204: Radiofrequency impedance
Method 2207: Radiofrequency sensitivity
Method 2205: Static discharge sensitivity
Moreover in order to be able to verify the response to transient disturbances (such as lightning induced
currents for example) it is necessary to measure the thermal time constant of the EED.

2.3.2 MIL-STD-1553 B (Data bus Monitor)

The data bus is the natural source of information to perform EMC system testing. In the MIL-STD-1553 B bus
a bus analyzer is connected to a coupler box to monitor the bus traffic. When a wrong parameter causes a
system failure, even if caused by interference the malfunction is fixed as a system failure. The aim of EMC
system testing is to determinate the safety margin when there are no evident malfunction.
When testing a digital system monitoring the parameters of the transmitted waveforms has little meaning if
the waveform distortion does not cause a wrong output data; additionally the wave distortion is not easily
related to a safety margin. The proposed test procedure is as described in the following.
The test procedure is divided in two parts: system characterization and measurements. During system
characterization the parameter under test is measured in condition of minimum interference, which means the
minimum number of equipment/subsystem activated. The parameter is measured as multiples of the LSB
(Least Significant Bit). For example we assume the case of an angular value comprised between –180 and
+180 degrees with increments of 1 LSB=0.01098 because of 16 bit quantization. In the following table the
characterization of the angle measured with 1183 samples is shown.
 45

Numerical
Statistical
values of the Deviation (si)
frequency (fi)
parameter
39.50650 9 -4
39.5170 50 -3
39.5280 152 -2
39.5390 303 -1
39.5500 420 0
39.5609 238 1
39.5719 11 2
total 1183

One measures the deviation si from the value with the highest statistical frequency fi=420 samples. It is
assumed that the probability density of the parameter under test is Gaussian; therefore in order to get a
characterization of the parameter statistic it is necessary to determine the mean value and the standard
deviation, which are calculated as follows:
N
 f i si  533
Sm = ∑ 
i =1 N 
= −
1183
= − 0 . 45505 LSB

N
f i s i2
σ = ∑ i =1 N
− S m2 = 1 . 1435 LSB

From the theory random variables it is known that 93.73% of the measurements fall within the interval

Vs− = Sm − 3σ Vs+ = Sm + 3σ

We assume that Mi and Ms represent the largest possible values still acceptable according to the manufacturer
specification even if they are outside the statistical tolerance interval.
When the interfering subsystems or the external environment are activated the parameter under test changes
assuming the values V i or V i − . +

Microstrip Trace
Hole Cut in the
Passes Trough
substrate
Microstrip Ferrite Toroid
Transmiss
ion Line
Trace Z0=50Ω
Iin
I0
R1 Ferrite Toroid
R2 wrapped with
N turns
Z0=50Ω
RL V0

Fig.2(a): Physical topology

The PSM is calculated as:

V i+ − V s+
PSM + =
M s − V s+
V s− − V i−
PSM − =
V s− − M i
46

These safety margins are based upon the actual performances of the system. They have been proven to be very
accurate and sensitive highlighting malfunctions which do not appear during functional tests. The only
drawback is represented by the need of a processing with a large mass memory in order to be able to collect a
large amount of data.

MIL-STD-1553 B (Interference direct drive)

Efforts to determine and quantify the susceptibility and vulnerability of avionic system and subsystem
components to electromagnetic interference (both intentional and unintentional) according to the ESM method
typically include the need of direct driving interference signals. In order to inject signals on the 1553 data bus
[4] is necessary to develop a suitable breakout box, which must have the following circuits:
Current sensor circuit
Voltage sensor circuit
Signal injection probe circuit

Current sensor circuit

The current sensor is located downstream of the direct injection point . Fig 2(a) illustrates the topology of the
current sensor.

Z0 = 50Ω R2

+
Vin Iin I0 R1 V0 RL
-

Fig.2(b): Equivalent electrical circuit used to drive the current sensor transfer function (Zc)

It is composed of a ferrite core wrapped with N turns which form the secondary winding. The sensed line
passed through the centre of the core and comprises the primary winding. A resistor network (R1 and R2), the
cable characteristic impedance and the cable termination RL load the secondary winding. The core is mounted
in a rectangular cutout in the board and the ground plane is removed in region of the cut-out to accommodate
the core. The equivalent circuit for the current sensor is shown in Fig.2(b).
The transfer impedance is defined as the ratio of the (sensor) output voltage V0 to the monitored line current
Iin:

V0 αRLω
Z C (ω ) = = j
I in (
N jω + α (R2L+RL ) )
where N is the number of turns on the current sensing toroid, ω is the angular frequency, L is the secondary
R1
winding self inductance and α =
R L + R1 + R 2

The inductance L is given by:

µ 0 µ r N 2W b
L= ln
2π a

where b(a) is the outer (inner) radius of the magnetic material, µ = µ0µr, is the permeability of the core and W
=b – a is the current probe width.
The high frequency asymptotic limit of the transfer impedance is:
αRL
Z CHF =
N
 47

while the low frequency asymptotic limit is:

b
ωRL Nµ 0 µ rW ln 
Z CLF = j a
2π (RL + R2 )

The reflected impedance of the sensor (the series impedance) introduced in the sensed line due to the presence
of the sensor given is given as:
R
Z Re f = sec2
N
where Rsec is the total secondary impedance composed of the series and parallel combinations of R1, R2 and RL.
Finally the 3dB frequency is given by:

1 α(R2 + RL )
f3dB =
2π L

It is the frequency where the sensor response declines by 1 2 of the maximum magnitude of the transfer
impedance.
The current sensor transformer is constructed of C2050 ferrite cylindrical core (a =0.235cm, b =0.480cm)
with a nominal relative permeability µr =50 at 100 MHz. The current sensor design utilized N =3 turns on the
secondary, resistance values of R1 =100Ohm, R2 = 0Ohm and RL =50Ohm (cable impedance).

Voltage sensor circuit

The voltage sensor probe circuit is a capacitively isolated voltage divider:

The circuit and components are shown in Fig .3(a). For this application the ability to monitor all the traffic on
data bus line required, but the isolation of the probe from any DC components on the line is necessary.

Microstrip
Transmission
Line Trace

Z0=50Ω

C=10 nF

R1

Z0=50Ω +
R2 RL - V0

Fig.3(a): physical topology

C
R
Vin 2 Z
0

R1 RL +
V0
-

Fig.3(b): Equivalent electrical circuit used to derive the voltage sensor transfer function
48

From the equivalent circuit shown in Fig.3(b): the transfer function for the voltage sensor circuit is:

Vout ωCγ
ZV (ω ) = = j
Vin 1 + jωC(R1 + γ )

where γ is the parallel combination of the sensor cable impedance and R2. The 3 dB break point of the circuit
is given by:

1 1
f 3 dB =
2π C (R1 + γ )

and is the frequency where the output voltage is down by 1 2 of the high frequency asymptotic value.
The monitor must be sensitive to frequencies characteristic of the 1553 bus. This consideration leads to the
selection of the following component values:
C = 10nF (rated to 100 V), R1 = 1kOhm, R2 =50Ohm, and RL = 50Ohm is the cable impedance. These values
result in a break point frequency of 15.5kHz.

Signal injection probe circuit

The signal injection circuit capacitively couples the direct drive signal to the driven transmission line.

Microstrip
Transmission
Line Trace

Z0=50Ω

R
Z0

Z0=50Ω

Vin

Fig. 4(a): Topology and physical layout

Source
Impedance = Z0

R
C
+
Vin Pulse Z0 Z0 V0
Source Microstrip
Transmission Line -
Impedance

Fig. 4(b): Equivalent circuit used to derive the injection circuit transfer function (ZI)

To prevent reflection in the power divider circuit when attached to the driven trace, it is also designed to
terminate the drive signal in a match load. Fig. 4(a) depicts the topology of the signal injection circuit and Fig.
4(b) shows its equivalent circuit.
 49

The capacitance and resistance values of the drive signal injection circuit are chosen to:
provide maximum coupling efficiency of the drive signal to the transmission line DC
isolate crosstalk between to transmission line traces
provide a matched impedance to the drive circuit when it is attached to a transmission line trace
The transfer function of the signal injection circuit is given by:

Vout (ω ) ωCZ 0
Z I (ω ) = = j
Vin (ω ) 1 + jωC (1.5Z 0 + R)

where the microstrip transmission line is assumed matched terminated on either side.
Consideration of the above issues leads to the selection of the following components values :
C =62pF and R = 25Ohm.

Identification Technique

Susceptibility tests are carried out by taking into account the correlation between the susceptibility signal and
the malfunction of the system, which is generally monitored with manual and/or visual methods. The use of
automatic monitoring system could greatly improve the accuracy of susceptibility tests which should address
susceptibility signals. In Fig. 5 a general schematic of the proposed approach is drown:
n(t)

System u(t)
Under +
Test

e(t)
s(t) ∑
i(t)

Adaptative u’(t )
Filter

where
i(t) and u(t) are the input and output signals of the system under test
n(t) is the random noise
u’(t) is the output of the adaptive filter
e(t) = u(t) – u’(t) is the error signal
s(t) is the susceptibility signal which can generate by an internal or external source

The adaptive filter is regulated by a suitable identification algorithms which estimate the parameters of the
system under test in the absence of the interference signal s(t). When the error e(t) is minimum the adaptive
filter identifies the performance of the system under test. The interference source is activated and any
susceptibility effects is monitored as a change of the error e(t). In this manner the malfunction can be
evaluated in a quantitative manner. Obviously the complexity of the identification system can go from a very
simple device when one wants to monitor a steady state signal to a very complex unit when a dynamic system
shall be controlled. A simple example of the proposed method is shown in Fig 6 where the parameters of a
sinewave (amplitude, frequency, and phase) shall be monitored:
50

a(t)=Asin(ω1t+φ)+n(t)
- e(t)
System under ∑
test s(t) +
sin(ω1t)

Frequency
Control x

Asin(ω1t+φ)
Amplitude and
Phase Control

Fig.6

In the two branches of the system two correlations systems are used: in the upper branch the signal a(t) of the
system under control shall be monitored, in the lower branch the same signal is

generated by an adaptive control algorithm.

When the susceptibility signals s(t) is activated any change in A, ω1 and φ are detected as a change of e(t).
Moreover by means of the adaptive algorithm it is possible to pinpoint which parameter was effected.

TESTS SEQUENCE

In the previous paragraph the main issues of EMC system testing have been examined. During the test
sequence the following points will be considered:
full coverage of operative modes
selection of representatives test conditions
performance of tests in the most favourable testing situations
It is essential to verify the following conditions:
avionic EUT input and output signals from the other stages and/or from EDSE are properly simulated
the reduced shielding effectiveness due to the lack of part of the structure does not impair the validity of test
results
suitable simulations are carried out to determinate the levels of interfering signals to be injected on the
structure in the presence of external electromagnetic sources (Lightning and High Intensity Radiated Field
(HIRF))

Both EMC intersystem and intrasystem testing are actually identified by two types of tests-electromagnetic
hazards and electromagnetic effects. In both cases the EEDs or squibs are instrumented to sense a heat rise in
the bridgewires; moreover the control functions of the system are monitored to determinate degradation or
system reliability according to the Safety Margin.
The internal device shall be operated according to their actual operatives modes in ground and flight
conditions. The test sequence shall be defined on the basis of the capabilities and performances of EGSE. The
activation of internal devices generates the background interference, which is

due to the spurious coupling of wanted signals. The test sequence includes the following phases:
activation of external and internal interference sources
monitoring of the parameters which are considered representative of system performances
Both activation and monitoring operations are required to prepare the EMC Test Matrix which defines the
actual test sequence.
In addition to interaction tests also bonding resistance and isolation measurements will be performed.
 51

ACTIVATION

The activation comprise the execution of all those operations which are performed to perform the wanted
mission and additionally those operations due to external sources which may be wanted such as external
transmitter emissions or unwanted such as lightning.

External electromagnetic sources

The external sources are simulated according to two test procedures:
Low Level Coupling / Field Testing
High Level Testing based on Modelling and / or Coupling Data

Low Level Coupling / Field testing

This procedure has the main purpose of defining the transfer function E field / induced current inside the
aircraft; it shall be conducted together with numerical and analytical investigations. The first point is to start
with analytical interference assessment regarding the most critical frequencies the aircraft does respond best
according to its design like structure, slots and so on followed by a numerical simulation of the surface
currents and the surface charges as a response to an electromagnetic field depending on the field parameters
like frequency polarization, field strength and angle of incidence. Experimental investigations are conducted
on the not powered system at a simulated phase

The investigations on the not powered system determine the transfer function from the outer field as well as
from the surface currents to the internal field and to the resonances and induced currents on different signal
wirings.
The tests with the not powered system are distinguished between field radiation and direct injection tests of
the electric and magnetic field equivalent.
These investigations are helpful and necessary to limit the investigation efforts at live system tests where
concentration of the tests runs is based on the information received from the analytical and numerical as well
as from the experimental investigations conducted with not powered systems.
The experimental validation can be conducted in the following three manners:
Low Level Direct Drive (LLDD)
This procedure can be used to measure the transfer function at low level between the skin current and the
currents on individual equipment wiring bundles. If the relationship between the external High Intensity
Radiated Field (HIRF) environment and skin current is known for all illumination angles and polarizations,
either by accurate mathematical modelling or use of the Low Level Swept Current (LLSC) test described in
the following, this skin current can be set up by direct injection into the aircraft structure (or part of it). The
resultants currents on the internal cables are measured with a currents probe and normalized to external unit
field strength so that they can be scaled to the appropriate HIRF environment. This test method has improved
sensitivity compared with the Low Level Swept Current (LLSC) test. It is best used for frequencies below first
structure resonance.
Low Level Swept Current (LLSC)
This procedure, which can be applied up to 400 MHz, is used to measure directly the transfer function
between the external field and the aircraft / EUT cable bundles currents. Since the transfer function relates
cable currents to the external field, the inducted bulk cable current test levels can be related to an external
field.

The structure is uniformly illuminated sequentially from all sides by both horizontally and vertically polarized
swept frequency fields,
and the currents induced on the internal cable bundles measured. The ratio of this current to the illuminating
field strength is computed and normalized to 1 V/m. This provides the transfer function in terms of induced
current per unit external field strength which can then be extrapolated to the required HIRF field strength by
multiplying the induced current at 1 V/m by the external HIRF field strength. The extrapolated HIRF currents
for all measured configurations for each bundle being assessed are overlaid and a worst case induced current
profile produced. These profiles can be compared with the induced current measured during the Bulk Current
Injection (BCI) test conducted on a simulation rig, where the actual installation cable bundles are used. The
comparison may not show equivalence if there are changes in installation (cable length, screening, bonding
and cable composition)
52

Low Level Swept Field (LLSF)

The test procedure, which is performed at frequencies higher than 100 MHz, is similar to LLSC. The internal
fields local to the EUT are measured instead of the cable bundle current and various techniques are used to
ensure that the maximum internal field in the vicinity of the EUT is measured.

High Level Testing

This procedure shall be conducted on the live system at either single stage level or a multi stage structure level
depending on the configuration and/or capabilities of the EGSE. The guidance and control components with
the required wiring are the basis for the data acquisition during the functional response tests with the fully
operational system.
The interfering source activation procedure can be conducted in the following manners
High Level Direct Drive Test
It is possible at frequencies normally below the structure resonance to inject high level currents directly into
the structure for lightning and external electromagnetic field simulation. It is essential that mathematical
modelling predictions or LLSC measurements are made to determine the skin current distribution that will
exist for different attachment points and paths (lightning) and for different polarizations and illumination
directions (electromagnetic fields) so that these can be accurately simulated during this test. This procedure
has the advantage of testing all systems simultaneously but is very restricted on frequency range.

EUT Bulk Current Injection

The purpose of this test, generally conducted at frequencies lower than 400 MHz, is to measure the current at
EUT malfunction or test level of the EUT when RF currents are injected onto its wiring via a current
transformer. The installed system is tested using BCI with test levels determined from LLDD test or LLSC
test. Each bundle in the system is tested by injection and measurement of the inducted current on that bundle.
If a bundle branches, then each relevant branch containing wiring of the system under test may need to be
tested.

During BCI testing the system shall be fully operational. Simultaneous multi-bundle bulk current injection
may be necessary or systems; where for example there are redundant/multi-channel architectures.

High Level EUT Field Illumination

When the internal RF field surrounding the EUT has been measured during LLSF test and extrapolated to that
which would exist if the aircraft was in the HIRF environment, then the EUT can be illuminated in this field
by localized internal illumination. This is providing that the radiating antenna if far enough away to ensure
that the total volume of the EUT and at least half a wavelength of the wiring is simultaneously and uniformly
illuminated during testing.

High Field Illumination

This procedure relies on being able to generate HIRF fields external to launch vehicle. Below 400 MHz the
overall system shall be uniformly illuminated. Above this frequency the illumination can become more
localized to the EUT providing that all parts of the EUT are illuminated and as a minimum at least 1
wavelength of associated wiring should be uniformly illuminated to the field.

For frequencies below 400 MHz the launch vehicle (or an isolated stage) is placed at sufficient separation
from the radiating antenna to ensure uniform illumination. It is illumined an all sides and for both horizontal
and vertical polarization.

The peak field shall be modulated with realistic modulation types. The field is calibrated by measuring the
field in the centre of the test volume prior to the placement of the launch vehicle. The EGSE necessary to
monitor possible malfunctions shall be located in areas where no susceptibility problems can occur.
 53

CONCLUSIONS

The application of state of the art technologies has taken to the design an development of test facilities which
are suitable for the performance of all EMC / HIRF tests that are necessary to obtain aircraft qualification
according to military standards or customer requirements.
In particular, the objective of performing accurate HIRF testing on the whole aircraft has been achieved

REFERENCES

B.Audone – Compatibilità elettromagnetica, McGraw-Hill, 1992

S.Ripamonti – Articolo:’HIRF /EMC Test Technologies and Methodologies’
MIL-STD-1576 – “Electroexplosive Subsystem Safety Requirements and Test Methods for Space System” July
1984
C.Courtney and alias – “Breakout Box Experiments of Electromagnetic Susceptibility of Aircraft Electronics”
IEEE on EMC November 1996
This page has been deliberately left blank

Page intentionnellement blanche

 55

3. APPLICABLE STANDARDS FOR MILITARY SYSTEMS

Standards/Specifications are important means for (military) systems including electrical/electronic equipment
to achieve Intra-System Electromagnetic Compatibility and to protect them sufficiently against
electromagnetic environment effects like e.g. “High Intensity Radiated Fields (HIRF)”, Lightning, HPM or
Electromagnetic Pulse (EMP).
Standards/Specifications will specify the electromagnetic environment parameters to be considered, they
include requirements on equipment and sometimes system design, they should define procedures, how to
demonstrate sufficient protection. They also should keep in mind how to guarantee sufficient protection
during service time of the system.
This chapter deals with an analysis of the existing Standards/Specifications which are mainly applied by
NATO respectively which might be applicable for the military systems.

3.1 Electromagnetic Effects to be Considered

The following electromagnetic effects will be considered in this document:
Intra-System Electromagnetic Compatibility
It means Electromagnetic Compatibility between all electrical/electronic equipment installed in a system
including the transmitters and receivers.
Intra-System EMC is the absolute preposition for the function of a system.

High Intensity Radiated Fields (HIRF)

HIRF describes the electromagnetic field strength environment, which can be expected from external
transmitters like broadcast, radar, or transmitters on other systems.

Lightning
Protection against natural lightning is required for different systems.
It includes :
- Effects on structure/structure components (“direct effects”) and
- Effects on electronic systems/equipment (“indirect effects”)

Electromagnetic Pulse (EMP)

It will be generated in nuclear explosions.
Two different types of pulses can be defined :
- the Exo-atmospheric EMP :
The explosion takes place in higher altitudes. The only effect is the EMP. It is generated in an area only
limited by the horizontal conditions. It is defined as a constant threat for this whole area.
- the Endo-atmospheric EMP :
The event takes place near the surface. The EMP is one of different other nuclear effects. The amplitude is
dependent on distance. The pulse is generally wider
Only the Exo-atmospheric pulse is considered in this document, because it is the more likely threat.

E- and P-Static
Caused by vibration, influences of the environment (“e.g. dust”) systems or parts of them might charge up to
extreme potentials. – Discharge might cause damage to electronic, personnel shock, ignition of fuel and
interference.

HPM (“High Power Microwaves”)

High Power Microwaves are likely to become a significant future threat. Extreme high fields might be
generated by special weapons to damage RF-sensors (“front door effects”) but also non-antenna equipment
like computers, etc (“back door effects”) of weapon systems depending on electrical/electronic systems.
The following areas are not considered in this document:
Electromagnetic Spectrum Control
Emitted interference of systems; too special
HERF
Hazards of Electromagnetic Radiation on Fuel
56

3.2 Survey of EMC-Relevant Standards/Specifications Required

Where Standards or Specifications should generally be available, is pointed out in fig. 3.-1. Not included in
this figure are management requirements, which are defined in different documents, too.

Environment
Most systems have to work sufficiently in a certain external electromagnetic environment. This can be
represented by e.g. HIRF, Lightning, the EMP, HPM or in some cases also by electrically charged-up
items/components etc., where the systems or equipment might come in contact with.
The environments are absolutely necessary as a basis for the system design and for system testing, if sufficient
protection shall be demonstrated.
Different environments might be applied for HIRF, Lightning and E-Static for different systems depending on
their special characteristics and tasks.
Requirements on Equipment
To achieve sufficient protection against the EM-effects, a balanced protection has to be realized in each case
between the protection measures on equipment level and the measures, which can be applied on system level
(e.g. shielding).
That means, the equipment installed in a system must generally fulfill some requirements with respect to
emitted interference as well as with respect to insusceptibility to signals coupled–in.
Standarised test setups and limits have been created to control the EMC-properties of the equipment.
Emitted interference and susceptibilities have to be considered for Intra-System EMC.
Susceptibilities only have to be controlled with respect to the electromagnetic environments. The levels,
which will be applied in this cases, correspond to the internal environments which will be coupled-in.
Equipment, which is qualified in accordance with an existing specification/standard, is very helpful for the
system designer. It also a preposition, if systems shall be modified.

Requirements on Systems
Significant protection must generally be realized on system level, especially with respect to the external
environment. – In principle it is not of interest, how the protection is realized, if the requirements are fulfilled
at the end.- It might be a too high grade of specification, too, if equipment and system measurements are
specified at same time.
Some general rules, however, should be considered for the design, e.g. about bonding, etc. These can be found
in many handbooks, where a lot of experience is concentrated.

System Testing
After having finished the development, it has to be demonstrated, that all requirements are fulfilled and that
sufficient hardening is available against the external electromagnetic effects.
Intra-System EMC has to be demonstrated as a basic requirement and protection against HIRF, Lightning,
EMP and HPM as required. In some rare cases it might also be necessary to make system measurements with
respect to E-Static (e.g. charging up a complete aircraft).
A lot of technical problems and uncertainties can be involved just into system measurements with respect to
external effects like HIRF, Lightning, HPM and sometimes EMP. The real threat can generally never be
completely simulated as well as all threat cases, which might come up in practice.
Agreed and proved procedures should be available.

Maintenance
EM protection measures are more and more involved in system safety aspects. This is applicable for Intra-
System EMC as well as for HIRF, Lightning, EMP and E-Static.
Some of the protection measures might become less effective caused by corrosion, damage, etc.
Methods should be available to control EM protection during life time.

Modifications
Many systems will be modified during life time. New or other equipment will be installed, parts of the
structure will be changed (e.g. exchange of metallic structure parts against Glass Fiber or Carbon Fiber ones in
the case of aircraft). Methods have to be available how to guarantee sufficient protection after such a process
without repeating a lot of expensive system testing.
These methods shall cover Intra-System EMC as well as all EM environmental effects.
Fig. 3.-1 : Survey of Standards/Specifications Required

57
58

3.4 Situation with “Existing Standards/Specifications”

General
The following groups of standards/specifications will be considered :
- STANAGs, created directly for NATO military systems
- MIL-STDs, responsible for military systems in the US, but also in a lot of other countries
- Standards made respectively for modern commercial aircraft :
A lot of work has already been performed by US and European specialists to create new standards to ensure
sufficient Lightning and HIRF protection for modern commercial aircraft.
- Standards/specifications for commercial electric/electronic equipment.
Other military standards exist, too, e.g. in Germany the “VG”-Standards or in Great Britain the British
Standards. In addition there are some very modern project related EMC standards in Europe, e.g. for the
aircraft EUROFIGHTER. - These documents are not considered here.

Intra-System EMC
General
The Intra-System EMC has to be considered as the absolute prerequisite for the function of a system, that
means it has to work without any malfunctions also if no outside EM effects are present.
Hardening a system only against the external EM effects will in most cases not be sufficient to achieve Intra-
System EMC, too. Different types of interference signals and different coupling paths are involved.
Intra-System EMC will be achieved by controlling all significant EMC interfaces of each individual installed
in a system very careful with respect to :
- limitation of interference emitted to the outside
- requiring a certain insusceptibility to signals arriving from the outside
The limits applied in both cases are based on practical experience. In combination with the properties of the
system and the usual system design rules (“bonding, cabling, etc”) they guarantee with a good probability the
Intra-System EMC.
The EMC properties of an equipment will generally be controlled by tests and limits for the interfaces pointed
out in fig. 3.-2.
Applying EMC controlled equipment, however, is not an absolute guarantee for sufficient functioning of a
system. System compatibility tests have to be carried out to demonstrate sufficient safety margins (6 to 20 dB)
for all functions of interest (at least for safety critical ones, in general also for critical ones). – Interaction
testing is generally not sufficient.
The Intra-system EMC can be affected by corrosion, damage caused by vibration, etc. It should therefor be
controlled during service-time.
Modifications may also change inside coupling conditions. Care has to be taken after installing new
equipment, exchanging parts of conductive structure against poor or non-conductive ones, etc.

Standards/Specifications Required
To achieve and to ensure Intra-System EMC during life time the following standards/specifications shall be
available (fig. 3.-1) :
- Requirements on equipment
- Procedures to demonstrate Intra-System EMC including safety margins
- Methods to control Intra-System EMC during life-time (maintenance)
These, however, can be combined with measures to control external EM effects, too.
- Methods for control of Intra-System EMC after modifications
No requirements have generally to exist on design of system. It is in the most cases up to the system designer,
how protection will be realized. A lot of guidelines and recommendations, however, is laid down in
Handbooks, etc.

Existing Standards/Specifications
A survey of all documents is presented in table 3.-1. – The full titles and the status can be found in the chapter
3.5 : “References”.
 59

STANAG‘s
Requirements on equipment :
Only a few documents exist, however, for the most critical systems. Equipment requirements are available for
aircraft (STANAG 3516) and for ships (STANAGs 4435, 4436, 4437). They are in a rework status. – Some
requirements on EEDs might be included in STANAG 4238 (in preparation, not available to industry).
Requirements on systems :
One document (STANAG 3659) defines some design requirements for (metallic) aircraft. Another document
(STANAG 4567) is in planning, which might also cover some design recommendations. – Some information
might also be found in STANAG 4238 (in preparation, not available to industry).
System test procedures :
Procedures for system testing are in a planning status for aircraft only (STANAG 7116). The document might
also include some procedures for Intra-System EMC testing.
Maintenance :
A document, which will generally cover maintenance and maybe modifications, too, is in preparation as
STANAG 7130.
Modifications :
No special rules exist how to proceed after a modification of a system, that means, how to evaluate the effect
of a modification on EMC properties and which tests have to be performed to demonstrate full compliance
again.

MIL-STD‘s
Requirements on equipment
With respect to equipment requirements the MIL-STD-461/462 exists, which is generally applied for
equipment of all systems.
Some susceptibility requirements can be found in MIL-STD-1512 for EED‘s.
Requirements on systems
Some design requirements for ships and spacecraft can be found in MIL-STD 1310G respectively MIL-
STD1541A and MIL-STD-1542B. – The old MIL-B-5087 corresponding to STANAG 3659 is no more
applicable. – A lot of guide and information, however, is available in various Handbooks.
System test procedures
No MIL-STD has been found with procedures for system testing.
Maintenance :
There is no document, which handles this field in detail.
Modifications :
No special document is available.

Commercial Aircraft Documents

Requirements on equipment
The EMC requirements for commercial aircraft equipment are laid down in RTCA/DO-160. The procedures
are mainly based on old MIL-STD versions.
Requirements on systems :
No design requirements have been found.
System test procedures
No procedures are defined.
Maintenance :
There will be some information available with respect to HIRF and Lightning Protection. These measures
might also be applicable here.
Modifications :
Not covered.
 60
Fig. 3.-2 : Survey of Test-Set Up’s and Limits typically available in EMC-Equipment Specification
 Environment Requirements on Design Requirem. System Test Maintenance Modifications
Equipment on System Procedures
General NA MIL-STD-461D ((STANAG 4567))? (( STANAG 7130))? (( STANAG 7130))?
MIL-STD-462D
Munition, Weapon NA MIL-STD-1512 (STANAG 4238)?
Systems incl. EED‘s (EED‘s)
(STANAG 4238)?
Military Aircraft NA STANAG 3516* STANAG 3659 (( STANAG 7116))?
MIL-STD-461D (metallic only)
MIL-STD-462D
Ships, NA STANAG 4435* MIL-ST-1310G
Surface, Metallic MIL-STD-461D
MIL-STD-462D
Ships, NA STANAG 4436*
Surface, Non-metallic MIL-STD-461D
MIL-STD-462D
Submarines NA STANAG 4437*
MIL-STD-461D
MIL-STD-462D
Space and Launch NA MIL-STD-461D MIL-STD1541A
Vehicles MIL-STD-462D MIL-STD-1542B
Ground Systems NA MIL-STD-461D
MIL-STD-462D
Commercial Aircraft NA RTCA/DO-160
Commercial Other NA EN‘s,
Systems IEC‘s

STANAG xxxx : Available to industry as latest edition (STANAG xxxx) : Not available to industry
STANAG xxxx* : Available to industry not as latest edition ((STANAG xxxx)) : Planning status
? not known if subject is included

Table 3.-1 : Standards/Specifications covering Intra-System EMC

61
62

Other Commercial Standards/Specifications

Electromagnetic Compatibility of commercial equipment in daily life or also concentrated in industrial plants
will generally be achieved by defining requirements on equipment only.
A lot of documents have been created in the last years for commercial equipment to define test set-ups and
limits for all EMC interfaces of interest like pointed out in fig.3.-1.
The test procedures applied are often very similar to the STANAG/MIL-STD ones. In many cases they are
better, respectively more modern from the point of EMC.
The limits for emitted interference are comparable, too. Conducted susceptibility requirements are generally
lower like in military documents, sometimes, however, they are also higher.
No special standards/specifications have been found with definition of system requirements, system tests,
maintenance procedures and modifications.

High Intensity Radiated Fields (HIRF)

General
“High Intensity Radiated Fields” cover the problems, which might come up by the electromagnetic fields
produced by radio transmitters, radar stations or transmitters on other military systems.
Modern systems are getting more and more vulnerable to these external fields. The reasons are mainly, that
electrical components are getting increasingly involved in also safety critical functions of the systems and that
modern structure materials like carbon or glass fiber will generally provide significantly less shielding to these
fields. In addition modern electronic components are in most cases more susceptible. More electromagnetic
sources might also be found today than in the past.
The area of HIRF is a very modern one. Extended activities took just place in the US and Europe to define
suitable environments for commercial aircraft and to create procedures how to demonstrate sufficient
hardening.

Standards/Specifications Required
Documents should be available for (fig. 3.-1) :
The HIRF environment
Requirements on equipment
Procedures to demonstrate sufficient protection
Methods to control HIRF protection life-time.
These, however, can be combined with measures to control Intra-System EMC and other external EM effects
Handling of modifications
Similar to Intra-System EMC no requirements have generally to exist on system design.

Existing Standards/Specifications
A survey of the existing situation can be found in table 3.-2.
STANAG‘s
Environment :
A worst case operational EM environment is defined in STANAG 1307 (restricted). An other environment is
included in STANAG 4234 especially for weapon systems including EED‘s. STANAG 3614 presents some
information (as an example) for military aircraft. – All environments are different. The reason, however,
might be, that STANAGs 4234 and 3614 are just in rework. The drafts are not available to industry.
Requirements on equipment
The relevant requirements on equipment are partly covered in the EMC equipment requirements (STANAG
3516 for aircraft, STANAGs 4435 and 4436 for surface ships) in the test “Susceptibility to Radiated Fields”by
definition of increased limits. – Requirements on EEDs might be included in STANAG 4238, which is not
available to industry.
Requirements on systems
Design requirements covering HIRF for weapon systems equipped with EEDs will be probably included in
STANAG 4238, which is a draft and is not available to industry.
System test procedures
System testing is described for weapon systems in STANAG 4324, which also is in rework and not available
for industry. – A special document is in planning status for military aircraft, which will probably also cover
HIRF (STANAG 7116).
 63

Maintenance and modifications :

A document is also planned to cover generally EM maintenance and maybe also modification aspects, which
will probably handle the HIRF problem, too. It is STANAG 7130.

MIL-STDs
Environment :
MIL-STD-464 defines different EM environments for military aircraft operating on ships, for surface ships,
space and launch vehicles, ground systems and all other applications. The hardest is the environment on ships.
All others are significantly lower.
MIL-STD-464 includes also data about the internal environment on ships (surface metallic/non-metallic,
submarine)
Requirements on equipment
MIL-STD-1512 covers the HIRF problem on equipment level for weapon systems equipped with EEDs.
MIL-STD 461/462 takes care of HIRF for equipment for almost all military systems by increased levels for
the radiation susceptibility test and also the “Bulk Current Injection”-test
Requirements on systems
The MIL-STD-1310G may also be applied for ships to get some improvement similar like the MIL-STD-
1542B for space and launch vehicles. Both standards, however, are not created for HIRF protection.
System test procedures
Nothing is available on MIL-STDs side, how sufficient hardening shall be demonstrated.
Maintenance and modifications
Nothing is also available, how HIRF maintenance and HIRF relevant modifications shall be handled.
Information about these subjects might, however, be included in different handbooks.

Commercial Aircraft Documents

A lot of work has been done in the last years from the US (SAE AE4R) and the European specialists
(EUROCAE WG 33) to create environment data and test procedures for commercial aircraft. This work has
almost be finished. The results are applied in the certification process for all modern commercial aircraft
already now.
Environment :
The “Certification Document” defines environments for fixed wing aircraft and helicopters. To save money in
design and testing, different environments have been defined, one for critical functions, a significantly lower
one for the essential functions. No special HIRF requirement is laid on all other functions (requirement only
with respect to Intra-System EMC).
Requirements on equipment
The special HIRF requirements on equipment can be found in the RTCA/DO 160 document in section 20.
HIRF is considered with respect to increased test levels for radiated susceptibility tests and for the “Bulk
Current Injection”-test, too.
Requirements on system
No special design requirements are defined in the new commercial aircraft documents.
System test procedures
The “Certification Document” defines test procedures for demonstration of sufficient hardening in the whole
frequency band from 10 kHz up to 40 GHz.
Maintenance and modifications
The document has recognized the great significance of maintenance with respect to HIRF . It includes some
general rules how to proceed.

Other Commercial Standards/Specifications

Standards for commercial equipment do not include a special HIRF requirement for systems up to now. The
equipment will be hardened, however, at least up to levels required in the equipment standards (living area : 3
V/m; industrial area : 10 V/m; higher levels possible).
 64
Environment Requirements on Design Requirem. System Test Maintenance Modifications
Equipment on System Procedures
General STANAG 1307 MIL-STD-461D (( STANAG 7130))? (( STANAG 7130))?
(restricted) MIL-STD-462D
Munition, Weapon STANAG 4234* (STANAG 4238 ) ( STANAG 4238 ) STANAG 4324*
Systems incl. EED‘s MIL-STD-464 MIL-STD-1512 MIL-STD-1385B
(EED‘s) (repl. by MIL 464)
Military Aircraft STANAG 3614* STANAG 3516* (( STANAG 7116))
(example) MIL-STD-461D
MIL-STD-464 MIL-STD-462D
(ship operat.)
Ships, MIL-STD-464 STANAG 4435* MIL-STD-1310G
Surface, Metallic (outside MIL-STD-461D
+ within) MIL-STD-462D
MIL-STD-464
Ships, MIL-STD-464 STANAG 4436*
Surface, Non-metallic (outside MIL-STD-461D
+ within) MIL-STD-462D
MIL-STD-464
Submarines MIL-STD-464 STANAG 4437*
(within) MIL-STD-461D
MIL-STD-462D
MIL-STD-464
Space and Launch MIL-STD-464 MIL-STD-461D MIL-STD-1542B
Vehicles MIL-STD-462D
Ground Systems MIL-STD-464 MIL-STD-461D
MIL-STD-462D
Commercial Aircraft HIRF Certification RTCA/DO-160 HIRF Certification (HIRF Certification (HIRF Certification
Document Section 20 Document Document) Document)
Commercial Systems
STANAG xxxx : Available to industry as latest edition (STANAG xxxx) : Not available to industry
STANAG xxxx* : Available to industry not as latest edition ((STANAG xxxx)) : Planning status
? not known if subject is included

Table 3.-2 : Standards/Specifications covering HIRF

 65

Lightning Protection
General
Lightning has become a great risk for modern systems equipped with electrical and electronic equipment, too.
This is especially the case for modern aircraft.
A lot of activities took therefore place between US specialists (SAE AE4L) and European ones (EUROCAE
WG 31) to discuss new requirements and new test methods to ensure lightning protection for modern
commercial aircraft. A lot of work has already been performed. Some documents have already been published
about environment data, zoning and equipment testing, which already represent the basis for certification
today. - The activities are still ongoing.
Many of the knowledge found during these activities can (and will) be taken over for lightning protection of
other systems, too (MIL-STD-1795A, responsible for lightning protection of military aircraft, e.g., will be
replaced by these documents, when they are finished).
Standards/Specifications Required
Similar to HIRF documents should be available for ( fig. 3.-1 ) :
- The Lightning environment
- Requirements on equipment
- Procedures to demonstrate sufficient protection
- Methods to control Lightning Protection during life-time.
These measures can partly be combined with measures to control Intra-System and the
external EM effects
- Handling of modifications
No special requirements without consideration of zoning must exist on system design.
Existing Standards/Specifications
A survey is presented in table 3.-3.
STANAG‘s
Environment :
It is covered by STANAG 4236. The last version available to industry is from March 1993. It includes the
Multiple Stroke, but not the Multiple Burst, which has been defined meanwhile.- What has also not been
defined is the considerable E-field, which will generally be available before a lightning strike. – A special
environment with some slightly increased data is included for munitions.
A new version is in preparation, which will probably cover the latest lightning environment data (“close
contact between WG 31 and the author of the new edition”).
Requirements on equipment
Nothing is available at this time for equipment testing and qualification.
The STANAG 4236, which has been published as a first draft (not available for industry), will probably cover
this field with respect to applicable test waveforms and limits.
The STANAG 4327 will probably include the test set-up`s and test procedures. – Both documents seem to
cover not only munitions and weapon systems including EEDs, but a wider variety of systems. (“close contact
of author of both STANAGs to EUROCAE WG 31”).
Requirements on systems
STANAG 3659 is available, which describes some requirements to system mainly for metallic aircraft and
mainly with respect to bonding.- STANAG 4238 (existent as 1. Edition, not available to industry) might
include some requirements for munitions and weapon systems equipped with EEDs.
System test procedures
No system test procedures exist up to now in the published STANAG versions. They will probably be
included in STANAG 4327, which has been prepared as a 1. edition and which is not available to industry
(“close contact of author to EUROCAE WG 31”). The main field, they will probably cover, seems to be
munitions and weapon system equipped with EEDs, but first discussions with the author indicate, that they
will take care of a lot of other systems, too. – It is not clear, if the new document will also cover military
aircraft, because this might be included in the planned STANAG 7116.
Maintenance and modifications :
Nothing exists today: It might , however, be covered by the planned STANAG 7130.
MIL-STDs
Environment :
The modern lightning environment is included in MIL-STD-464. It is in line with the latest knowledge also
about aircraft threat and describes all current waveforms incl. Multiple Stroke and Multiple Burst as well as
the waveforms to protect against electric fields.
66

The MIL-STD 1757A, applied for aircraft lightning protection for many years, has been cancelled meanwhile.
The MIL-STD-1795A, which is still applicable today, will be cancelled as soon as the relevant documents for
the commercial (chapter 4.4.3.3.) have been finished and will be replaced by them. The document includes
already the Multiple Burst, but in the old version with 24 sets of pulse packages.
Requirements on equipment
Mil STD-1512 defines some requirements on EED circuits on the ground. – Nothing is available for
component and equipment testing anymore, the leak, however, is closed by application of the new methods
and limits for commercial aircraft.
Requirements on systems
Nothing is directly specified, but a lot of handbooks are available how to protect systems also against
lightning. – The MIL-STD-1795 includes some general requirements.
System test procedures
Nothing available, but the methods in preparation for the commercial aircraft will be taken over as a guide.
Maintenance and modifications :
Nothing available. Handbooks, however, might include some material.
Commercial Aircraft Documents
Environment :
It is very well defined in ED 84 / SAE ARP 5412 . It includes the latest knowledge about lightning parameters
not only with relation to aircraft.
Requirements on equipment
These are very well defined in RTCA/DO 160, Section 23 for “Lightning Direct Effects” (this means structure
components) and in Section 22 for “Lightning Transient Susceptibility” (this means for testing of
electric/electronic equipment). – The waveforms applied and the limits will also be included in ED 84 / SAE
ARP 5412, which might become the leading document. The test procedures will be included in a lightning
testing document, which is already in preparation by the SAE/EUROCAE specialists.
Requirements on systems
Nothing than how to define the lightning threat zones for aircraft is defined as a system requirement. The rules
are included in ED 91 / SAE ARP 5414. They are significantly different to what has been defined in the MIL-
STDs up to now.
System test procedures
A document is in preparation by the SAE and EUROCAE specialists, which will cover this field completely.
Maintenance and modifications :
These areas might be described in a “User`s Guide”, which is in preparation, too. Some guide is already given
for modifications in ED 81 / SAE AE 4L- 87-3 document.
Other Commercial Standards/Specifications
Environment :
Some is available at IEC.
IEC 1024-1-1 handles protection of structure of ground facilities against direct effects (“damage of
structure”), IEC 61312-1-2 protection against the indirect effects of equipment installed in the ground
facilities. – Three different external threat levels have been assumed in each case, which are slightly different.
The number of the action integral, for example, is larger for all 3 levels than to be defined for aircraft up to
now (“factor of 5 for the largest threat level”).
Requirements on equipment
The IEC 61 312-4 is available for lightning protection of equipment installed in buildings.
Requirements on systems
IEC 61662 presents guide how to assess the risk of damage , which will be caused by lightning.
IEC 61024-1-1/2 handle lightning protection of buildings.
IEC 61312 describes rules, how to protect equipment installed in buildings against the indirect effects of
lightning.
System test procedures
Nothing is available how to demonstrate lightning protection for great systems similar to an aircraft etc.
Maintenance and modifications :
IEC 61024-1-2 gives some guide for maintenance and inspection of lightning protection facilities for
buildings.
 Environment Requirements on Design Requirem. System Test Maintenance Modifications
Equipment on System Procedures
General STANAG 4236* (STANAG 4327) (STANAG 4327) (( STANAG 7130))? (( STANAG 7130))?
MIL-STD-464 (4236 new) All systems ? All systems?
Munitions, Weapon STANAG 4236* MIL-STD-1512 ( STANAG 4238 )?
Systems incl. EED`s
Military Aircraft MIL-STD-1795A** STANAG 3659 (( STANAG 7116 ))?
MIL-STD-1795A**
Ships,
Surface, Metallic
Ships,
Surface, Non-metallic
Submarine
Space and Launch
Vehicles
Ground Systems IEC 61024-1/2 IEC 61312-4 IEC 61312-1/2 IEC 61024-2
IEC 61662
Commercial Aircraft ED84/SAE ARP RTCA/DO-160 ED91/SAE ARP Testing User`s Guide ? ED 81 / SAE AE
5412 Sections 22/23 5414 Standard 4L- 87-3
ED84/SAE ARP (Zoning) (DRAFT)
5412 User`s Guide ?
Testing
STANDARD
Commercial Other IEC 61024-1/2 IEC 61312-4 IEC 61312-1/2 IEC 61024-2
Systems IEC 61663-1

STANAG xxxx : Available to industry as latest edition (STANAG xxxx) : Not available to industry
STANAG xxxx* : Available to industry not as latest edition ((STANAG xxxx)) : Planning status
? not known if subject is included

** will be replaced by commercial aircraft documents as soon as available

Table 3.-3 : Standards/Specifications Covering Lightning Protection

67
68

Electromagnetic Pulse (EMP)

General
The most likely and critical threat is the Exo-atmospheric EMP, also called HEMP (“High Altitude
Electromagnetic Pulse”). Most standards and documents available will therefore be related to this pulse only.
3.4.5.2 Standards/Specifications Required
Like for lightning protection should be available fig.3.-1 :
- The EMP environment
- Requirements on equipment
- Procedures to demonstrate sufficient protection
- Methods to control EMP hardening during life-time.
These measures can partly be combined with measures to control Intra-System EMC and the external EM
effects.
- Handling of modifications
No special requirements must generally exist on system design. There can be, however, an
exception, which has been realized for EMP. If the design requirements on a system specified and realized
very carefully, it is not necessary to know the real detailed threat (method applied in MIL-STD 188-125A for
protection of Ground Based C4 Facilities).
Existing Standards/Specifications
A survey is presented in table 3.-4.
STANAG‘s
Environment :
It might be defined in STANAG 4145, which is identical with the AEP-4.
Requirements on equipment
STANAG 4145 will probably include a lot of information
Requirements on systems
Some requirements will probably be described in STANAG 4145.
System test procedures
STANAG 4416 is involved in testing of munitions against the EMP.
Some might also be planned in STANAG 7116 (planning status) for military aircraft.
Maintenance and modifications :
Guide might be presented in STANAG 7130 (planning status)
MIL-STDs
Environment :
The 5ns-rise time NEMP is defined in MIL-STD 464.
More information will probably be found in MIL-STD-2119 (restricted).
Requirements on equipment
A test method and a limit id described in MIL-STD-462.
Requirements on systems
Requirements on system design are included in detail in MIL-STD-188-125A applicable for C4-Ground
Systems.
System test procedures
Nothing available. It might be included in Handbooks.
Maintenance and modifications :
Nothing available. It might be included in Handbooks
Commercial Aircraft
Not applicable.
Other Commercial Standards/Specifications
Environment :
Some data might be available in IEC 61000-2-9/10 for radiated and conducted environment.
Requirements on equipment
IEC 61000-4-24 presents information, how to test protection devices.
Requirements on systems
IEC 61000-5-3 handles protection concepts against the EMP.
IEC 61000-5-4/5 specifies protection devices for radiated and conducted disturbances.
 Environment Requirements on Design Requirem. System Test Maintenance Modifications
Equipment on System Procedures
General STANAG 4145 ? STANAG 4145? STANAG 4145 ? (( STANAG 7130))? (( STANAG 7130))?
(AEP 4) (AEP 4) (AEP 4) All systems ? All systems?
MIL-STD-464 MIL-STD-461D IEC 61000-5-3/4/5
MIL-STD-2119 MIL-STD-462D
(restricted)
IEC 61000-2-9/10 IEC 61000-4-24
(Prot. Devices)
Munitions, Weapon STANAG 4416
Systems incl. EED`s
Military Aircraft ((STANAG 7116))
Ships,
Surface, Metallic
Ships,
Surface, Non-metallic
Submarine

Space and Launch

Vehicles
Ground Systems MIL-STD-188-125A
Commercial Aircraft
Commercial Other
Systems

STANAG xxxx : Available to industry as latest edition (STANAG xxxx) : Not available to industry
STANAG xxxx* : Available to industry not as latest edition ((STANAG xxxx)) : Planning status
? not known if subject is included

Table 3.-4 : Standards/Specifications Covering the EMP

69
 70
Environment Requirements on Design Requirem. System Test Maintenance Modifications
Equipment on System Procedures
General (( STANAG 7130))? (( STANAG 7130))?
All systems ? All systems?
Munitions, Weapon STANAG 4235 (STANAG 4490) STANAG 4434 STANAG 4239
Systems incl. EED`s STANAG 4239 MIL-STD-1512 (packaging)
MIL-STD-1512 (EEDs)
Military Aircraft MIL-STD-464 STANAG 3659 ((STANAG
(some guide) (metallic) 7116))??
Ships,
Surface, Metallic
Ships,
Surface, Non-metallic
Submarine

Space and Launch

Vehicles
Ground Systems
Commercial Aircraft
Commercial Other EN 61000-4-2 EN 61000-4-2 IEC 61087
Systems IEC 61340-5-1/2 (charged surfaces)
(devices) IEC 61340-4-1
(floor covering)

STANAG xxxx : Available to industry as latest edition (STANAG xxxx) : Not available to industry
STANAG xxxx* : Available to industry not as latest edition ((STANAG xxxx)) : Planning status
? not known if subject is included

Table 3.-5 : Standards/Specifications Covering E-Static

 71

E- and P-Static
General
Electrostatic effects might cause a lot of problems with respect to performance degradation or damage of
electronic components, ordnance hazards, fuel ignition, system interference (e.g. generation of noise into
antenna systems) and personnel shocks.
In most cases the Intra-System E-Static problems of a system are solved by design requirements with respect
to avoid generation of charge (e.g. conductive paints), earthing and bonding measures to distribute the
generated charge and in the case of aircraft by installing special discharge components to reduce the charge on
the system.
The main problems, which have generally to be considered, are the cases, where electronic components or
equipment and EDDs or weapon system equipped with EEDs will come in contact with other charged up
systems or personnel.
Standards/Specifications Required
- Some E-static threat data, which can be expected
- Requirements on equipment/components, where E-Static might be a risk
- Procedures to demonstrate sufficient protection
- Methods to control protection during life-time.
These measures can partly be combined with measures to control all other EM effects.
- Handling of modifications

Existing Standards/Specifications
A survey is presented in table 3.-5.

STANAG‘s
Environment :
STANAG 4235 specifies two environments for weapon systems including EEDs. The first is defined with
respect to handling by personnel (25 kV ou of 500 pF across 500 to 5000 Ohms), the second considers
transport e.g. in helicopters ( 300 kV out of 1000 pF across 0 to 1 Ohm).
The same environment is also included in STANAG 4239.
Requirements on equipment
STANAG 4490 seem to define requirements on EEDs. The document is a first draft and is not available to
industry.
Requirements on systems
STANAG 3659 includes some requirements with respect to bonding, which are also applicable to E-Static.
Only metallic aircraft are considered.
STANAG 4434 specifies requirements for packing of equipment/systems susceptible to E-Static.
System test procedures
STANAG 4239 describes good methods, how to test weapons.
The STANAG 7116 in preparation for aircraft might also include something about E-Static (unlikely).

Maintenance and modifications :

Guide might be presented in STANAG 7130 (planning status)

MIL-STDs
Environment :
MIL-STD-1512 includes an environment on EEDs. (25 KV out of 500 pF across 5000 Ohms) in the
version from 1972).
Requirements on equipment
MIL-STD-1512 for EEDs only.
Requirements on systems
Some guide is presented in MIL-STD-464 which charges might be built up in aircraft.
System test procedures
Nothing available. It might be included in Handbooks.
72

Maintenance and modifications :

Nothing available. It might be included in Handbooks
Commercial Aircraft
No requirement or test has been defined for commercial aircraft electronic equipment in the RTCA/DO 160.
Other Commercial Standards/Specifications
Environment :
EN 61000-4-2 defines as an environment for ESD testing 4-8 kV out of 150 pF across 330 Ohms.
Requirements on equipment
EN 61000-4-2 has to be applied.
IEC 61340-5-1/2 are involved in protection of electronic devices.
Requirements on systems
IEC 61087 is a guide to evaluate discharges from charged surfaces.
IEC 61340-4-1 handles behaviour of floor coverings.
System testing:, Maintenance and Modifications :
Nothing available.

High Power Microwaves (HPM)

Nothing has been specified up to now with respect to HPM.

References
STANAGS (Status : August 1998)

1. STANAG 1307:Maximum NATO Naval Operational EM Environment. Produced by Radio and Radar
Edition 2, 4th Febr. 1997

2. STANAG 3516:Electromagnetic Interference and Test Methods for Aircraft. Electrical and Electronic
Equipment. Edition 3, 10th May 1993. Edition 4, 2.DRAFT in preparation. Latest edition not available to
industry!

3. STANAG 3614:Electromagnetic Compatibility of Aircraft Systems” Edition 3, 8th June 1989 Edition 4,
1.DRAFT in preparation. Latest edition not available to industry!

4. STANAG 3659:Electrical Bonding Requirements for Metallic Aircraft Systems. Edition3, 20th Nov. 1998

5. STANAG 4145:Nuclear Survivability Criteria for Armed Forces Material and Installations (identical with
AEP-4)

6. STANAG 4234:Electromagnetic Radiation ( 200 kHz to 40 GHz) Environment Affecting the Design of
Materiel for Use by NATO Forces. Edition 1, 7th July 1992. Edition 2, 1. DRAFT in preparation. Latest
edition not available to industry!

7. STANAG 4235:Electrostatic Environmental Conditions Affecting the Design of Material for Use by NATO
Forces” Edition 1, 29th Jan. 1993. Edition 2, 1. DRAFT in preparation. Latest edition not available to industry!

8. STANAG 4236:Lightning Environmental Conditions Affective the Design of Materiel, for Use by the
NATO Forces” Edition 1, 8th March 1993. Edition 2, 1. DRAFT in preparation. Latest edition not available to
industry

9. STANAG 4238: Munition Design, Principles, Electromagnetic Environment. Edition 1, 1. DRAFT in

preparation.. Not available to industry

10. STANAG 4239:Electrostatic Discharge Munitions Test Procedures. Edition 1, 13th Oct.1997

11. STANAG 4324 :Electromagnetic radiation (Radio Frequency) Test Information to Determine the Safety
and Suitability for Service of EED‘s and Associated Electronic Systems in Munitions and Weapon Systems.
Edition 1, 25th June1991. Edition 2 , 1. DRAFT in preparation. Latest edition not available to industry
 73

12. STANAG 4327 : Lightning Test Procedures to Determine the Safety and Suitability for Service of EED‘s
and Associated Electronic Systems in Munitions and Weapon Systems. Edition 1 , 1. DRAFT in preparation
New ! Not available to industry

13. STANAG 4416 : Nuclear EMP Testing of Munitions Containing EED‘s AOP 28

14. STANAG 4434 : NATO Standard Packing for Susceptible to Damage by Electrostatic Discharge Edition1,
DRAFT 1 in preparation. New ! Not available to industry

15. STANAG 4435 : Electromagnetic Compatibility Testing Procedure and Requirements for Naval Electrical
and Electronic Equipment (Surface Ships, Metallic Hull) Edition 1, 2nd March 1993. Edition 2, 1.DRAFT in
preparation. Latest edition not available to industry

16.STANAG 4436 : Electromagnetic Compatibility Testing Procedure and Requirements for Nava Electrical
and Electronic Equipment (Surface Ships, Non-metallic Hull) Edition 1, 2nd March 1993. Edition 2,
1.DRAFT in preparation. Latest edition not available to industry

17. STANAG 4437 : Electromagnetic Compatibility Testing Procedure and Requirements for Naval Electrical
and Electronic Equipment (Submarines) Edition 1, 29th June 1994. Edition 2, 1.DRAFT in preparation. Latest
edition not available to industry

18. STANAG 4490 : Explosives, Electrostatic Discharge Sensitivity Edition1, DRAFT 1 in preparation.
New ! Not available to industry

19. STANAG 4567 : Unified Procedures for Electromagnetic Protection. Planned

20. STANAG 7116 : Verification Methodology for Electromagnetic hardness of Aircraft. Planned

21. STANAG 7129 : Electromagnetic Compatibility Operational Awareness Procedures. Planned

22. STANAG 7130 : In-Service Maintenance/ Validation of EM Hardening Measures. Planned

MIL-STDs (Status : August 1999)

1. MIL-STD-461D : Requirements for the Control of Electromagnetic Interference,

Emissions and Susceptibility
11th Jan. 1993

2. MIL-STD-462D : Measurement of Electromagnetic Interference Characteristics

Emissions and Susceptibility
11th Jan. 1993

3. MIL-STD-464 : Electromagnetic Environmental Effects, Requirements for Systems

18th March 1997
Superseding :
MIL-STD 1818A, MIL-E-6051D, MIL-B-5087B,
MIL-STD-1385B

4. MIL-STD-1310G: Shipboard Bonding, Grounding and Other Techniques for EMC

and Safety
28th June 1996

5. MIL-STD-1512 : Electroexplosive Subsystems, Electrically Initiated, Design

Requirements and Test Methods
Note 1
74

6. MIL-STD-1541A : Electromagnetic Compatibility Requirements for Space Systems

30th Dec. 1987
Will become a Guidance Book

7. MIL-STD-1542B: Electromagnetic Compatibility and Grounding Requirements for

Space System Facilities
1st March 1988
Will become a Standard Practice Document

8. MIL-STD-1605 : Procedures for Conducting a Shipboard EMI Survey

(Surface Ships)
20th Apr. 1973

9. MIL-STD-1795A: Lightning Protection of Aerospace Vehicles and Hardware

1st Aug 1989
Will be canceled, when the documents mentioned in 7.3 as
reference are available
10. MIL-STD-2169 : High Altitude Electromagnetic Pulse

11. MIL-STD-188-125A : High Altitude Electromagnetic Pulse Protection for Ground

Based C4 Facilities Performing Critical,
Time Urgent Missions”

12. MIL-STD-220A: Method of Insertion Loss Measurement for Radio-Frequency Filters

Canceled
13. MIL-STD-285 : Attenuation Measure for Enclosure EM shielding for Electronic Test
Purposes, Method of
Canceled; to be replaced by IEEE 299-1991

Commercial Aircraft Documents:

1. RTCA/DO-160 : Environmental Conditions and Test Procedures for Airborn

Equipment
Sections cover Intra-system EMC, HIRF and
Lightning :
Section 20 : Radio Frequency Susceptibility
(Radiated and Conducted)
Section 22 : Lightning Transient
Susceptibility
Section 23 : Lightning Direct Effects
Other sections : Intra-system EMC

2. ED 84 / SAE ARP 5412: Aircraft Lightning Environment and Related Test

Waveforms
Sept.1997 ED 84, May 1999 SAE
3. ED 91 / SAE ARP 5414: Aircraft Lightning Zoning
July 1998 ED 84, May 1999 SAE
4. ED ? / SAE ARP ?: Aircraft Lightning Testing
DRAFT

ED 81 / SAE AE4L-87-3-Rev.C: Certification of Aircraft Electrical/Electronic

Systems for the Indirect Effects of Lightning”
May 1996
 75

6. User`s Guide : In preparation

7. ED ? / SAE AE4R ?: Certification of Aircraft Electrical/Electronic

Systems for
Operation in High Intensity Radiated
Fields (HIRF)”
DRAFT
Other Commercial Standards/Specifications :
Of main interest in this case are the EN/ICE/CISPR Standards available.
At least the following documents should be taken in consideration :
3.5.4.1 EMC :
Emissions (conducted and radiated) :
- EN 55011 (or CISPR 11) for ISM equipment
- EN 55013 for broadcast receivers
- EN 55014 for household equipment
- EN 55015 for lighting equipment
- EN 55022 for IT (information technology)
The tests are based are based on the (old) CISPR standards. All include measuring methods and test set-up`s.
For power mains related emissions, the following apply:
- EN 61000-3-2 for harmonics (or IEC 1000-3-2)
- EN 61000-3-3 for flicker

Immunity/Susceptibility Testing :
The following documents should be considered in this context :
- EN 61000-4-2 for ESD
- EN 61000-4-3 for radiated field RF immunity
- EN 61000-4-4 for EFT (electric fast transients or burst)
- EN 61000-4-5 for Surge
- EN 61000-4-6 for conducted RF immunity
- EN 61000-4-8 for power frequency (50 Hz) magnetic field immunity
- EN 61000-4-9 and 10 for pulsed and oscillatory magnetic fields (not used)
- EN 61000-4-11 for voltage dips
- other in preparation, but questioned at the moment if they are relevant in
practice.
There are also Product Standards available. They give the typical requirements for an individual, e.g. cars.
Measuring methods however (and also some pre-defined levels) are given in the basic standards. - When there
is no Product Standards available for a special product, a 'generic standard' can be used as a reference.
There are no standards available for large systems without :
- lifts and elevators: EN 12015 and EN 12016
- agricultural machines and ground moving machines: EN 14982
- automotive directive in Europe 95/54
(with reference to some international ISO standards)
In some cases, combined with subassembly testing, risk analysis is needed in order to reduce the EMC testing
to relevant units. Risk analysis and safety related EMC testing is described in:
- EN 61000-1-2 for EMC and functional safety
- EN 61508 subparts 1-7:functional safety of electronic systems AND software
For cabling (especially data communication), generic and installation standards are expected in the near
future:
- EN 50173 and EN 50174
- IEC 11801
Further information can be found for :
- for EN standards of CENELEC: www.cenelec.be
- for international standards of IEC:www.iec.ch
76

3.5.4.2 Lightning Protection :

- IEC 1024-1 Ed.1 / ENV 61024-1 :
Protection of structures against lightning - Part 1: General principles

- IEC 61024-1-1 Ed. 1.0 :

Protection of structures against lightning - Part 1: General principles –
Section 1: Guide A: Selection of protection levels for lightning protection systems

- IEC 61024-1-2 Ed. 1.0 :

Protection of structures against lightning - Part 1-2: General principles –
Guide B - Design, installation, maintenance and inspection of lightning protection systems

- IEC 61312-1 Ed. 1.0 :

Protection against lightning electromagnetic impulse –
Part 1: General principles

- IEC 61312-2 TS Ed. 1.0 :

Protection against lightning electromagnetic impulse (LEMP) - Part 2: Shielding of structures,
bonding inside structures and earthing

- IEC 61312-4 TR2 Ed. 1.0

Protection against lightning electromagnetic impulse - Part 4: Protection of equipment in
existing structures

- IEC 61662 TR2 Ed. 1.0 :

Assessment of the risk of damage due to lightning

- IEC 61662 Amd.1 TR2 Ed. 1.0

Amendment No. 1
- IEC 61663-1 Ed. 1.0 :
Lightning protection - Telecommunication lines - Part 1: Fibre optic installations

3.5.4.3 Electromagnetic Pulse (EMP) :

- IEC 61000-2-9 Ed. 1.0 :
Electromagnetic compatibility (EMC) - Part 2: Environment - Section 9: Description of
HEMP environment - Radiated disturbance.
Basic EMC publication

- IEC 61000-2-10 Ed. 1.0 :

Electromagnetic compatibility (EMC) - Part 2-10: Environment - Description of HEMP
environment - Conducted disturbance

- IEC 61000-4-24 Ed. 1.0 :

Electromagnetic compatibility (EMC) - Part 4: Testing and measurement techniques - Section
24: Test methods for protective devices for HEMP conducted disturbance - Basic EMC
Publication

- IEC 61000-5-3 TR Ed. 1.0 :

HEMP protection Electromagnetic compatibility (EMC) - Part 5-3: Installation and mitigation
guidelines concepts
- IEC 61000-5-4 TR2 Ed. 1.0 :
Electromagnetic compatibility (EMC) - Part 5: Installation and mitigation guidelines - Section
4: Immunity to HEMP - Specification for protective devices against HEMP radiated
disturbance.
Basic EMC Publication
 77

- IEC 61000-5-5 Ed. 1.0 :

Electromagnetic compatibility (EMC) - Part 5: Installation and mitigation guidelines - Section 5:
Specification of protective devices for HEMP conducted disturbance.
Basic EMC Publication

3.5.4.4 Electro-Statics :
- IEC 61087 TR2 Ed. 1.0 :
Guide for evaluating the discharges from a charged surface

- IEC 61340-4-1 Ed. 1.0 :

Electrostatics - Part 4: Standard test methods for specific applications –
Section 1: Electrostatic behaviour of floor coverings and installed floors

- IEC 61340-5-1 TR2 Ed. 1.0 :

Electrostatics - Part 5-1: Protection of electronic devices from electrostatic phenomena
General requirements

- IEC 61340-5-2 TS Ed. 1.0 :

Electrostatics - Part 5-2: Protection of electronic devices from electrostatic phenomena User
guide
This page has been deliberately left blank

Page intentionnellement blanche

 79

4. EVALUATION OF STANDARDS AND PROPOSALS

FOR IMPROVEMENT

4.1 Criteria for Improvement

The following criteria will be applied looking for improvement of the existing situation :
Reduction of risks which might exist today
Although the different areas are covered by applicable standards/specifications, there might still be a
risk, because the documents are not harmonized. Equipment or systems might be qualified to a certain
standard, which is no more sufficient today or which require other levels.
Reduction of effort
Hardening of systems against EM effects and demonstration of sufficient protection as well as
maintenance activities requires sometimes a lot of effort. As far as possible it is pointed out, where reduction
might be achieved without increase of risk.
Requirements by future techniques
The technique applied in the systems is always in progress. If some problems might be expected in
next future, it will be pointed out.

4.2 Consideration of the Different Electromagnetic Effects

4.2.1 Intra-System EMC
The existing situation is pointed out in table 3.-1. – Intra-System EMC will be achieved by requirements on
equipment side and realization of protection measures on system side. System test procedures have to be
applied to demonstrate Intra-System EMC. Maintenance measures are very often necessary to guarantee the
EMC. Of interest are modifications, such on equipment or also structure side. They can have a large influence
on the EMC-behaviour.
Requirements on equipment
Requirements on equipment are probably laid down in STANAG 4238 for EEDs (first draft in
preparation, not available to industry), for military aircraft in STANAG 3516 and for metallic and non-
metallic surface ships in STANAGs 4435/4436. The requirements for submarines are included in STANAG
4437. – All these STANAGs are in an update status. The drafts are not available to industry. It is, however,
assumed, that they will follow the latest edition of the MIL-STD-461/462.
That means, the most important military systems are covered in this case and the latest status
of technique will probably be included soon. – In the case, where requirements are not specified in a
STANAG (e.g. for missiles), the MIL-STD-461D/462D might be applied.
There seems not to be any technical risk with respect to the Intra-System EMC based on military
specifications.
Requirements on equipment exist also in the commercial area. The RTCA/DO 160 D has to be
mentioned for commercial airborne equipment, a lot of EN`s and IEC`s are available for commercial ground
equipment.

Reduction of effort :
The following can be mentioned here :
- Reduction of effort for testing :
Radiated susceptibility have to be performed in the military specifications starting at a frequency range of 10
kHz up to max. 40 GHz. There are a lot of problems just in the lower frequency range. To perform this test
perfectly, expensive absorbers would be required. The main coupling, however, will take place in the lower
frequency range via cabling. In the committees for commercial aircraft it was therefore decided, to apply the
current injection test only in the lower frequency range and to start with radiated susceptibility testing at 100
MHz. A lot of money can be saved by this procedure without any increase of a risk.

- Reduction of effort by use of commercial equipment :

Sufficient standards/specifications are available to control EMC-interfaces of commercial equipment. The
RTCA/DO 160 D is applicable for commercial airborne equipment, a lot of ENs and IECs for ground
80

equipment. If a comparison of the different documents with the military requirements would be performed, the
way might be open to apply a lot of commercial equipment in different military systems.

Future requirements :

It might be necessary to define specifications with respect to “Modular Avionic”. A lot of PCBs (printed
circuit boards) offered by different manufacturers will be integrated in one common case. New tests and limits
are required to ensure EMC in this case.

Requirements on system
STANAG 4567 is in planning status with unknown list of content.- STANAG 3569 includes some bonding
requirements and guidelines, but for metallic aircraft only. Some special MIL-STDs are available for ship,
space and launch application.
There are not too many standards/specifications available in this case, but this does not mean any risk.
Development of the system is generally under the responsibility of the system manufacturer. A lot of
handbooks etc. are available for his support. Existing specifications, however, should also consider new
materials (e.g. CFC for aircraft)
System test procedures
Intra-System EMC protection has to be demonstrated by testing. Interaction tests only are in most cases not
sufficient. Safety margins have to be demonstrated for all electrical circuits/functions of interest.
Nothing applicable has been specified up to now with the only exception of coupling into the EED-circuits,
where the HIRF test methods might be applied. Test procedures are also not available in the commercial area.
Testing will mainly take place in large test houses, which have a lot of experience. They apply proven
methods, which, however, might differ from test house to test house,
Some general rules and procedures should be defined in this case, that the results get comparable and that all
the experience available is collected. This should be done for conducted interference as well as for radiated
one including antenna to antenna coupling problems.
Maintenance
Safety of systems might be more and more affected by defect EMC protection measures. Maintenance
has to be performed. STANAG 7130 is in an planning status, which will probably cover this area.
Modifications
Change or repair of structure, installation of additional equipment or cabling might have a large
influence to EMC protection. A lot of money might be involved, if all the expensive system tests have to be
repeated. Rules and methods shall be defined – based on the experience available- how to proceed (e.g.
including increased application of computer programs). – These methods could also be included in STANAG
7130 (in planning status).
4.2.2 High Intensity Radiated Fields (HIRF)
The situation is also presented in table 3.-2.
Environment
The latest environment defined by STANAG is included in the 1307. It presents the highest levels
produced by radio and radar, which might ever been found in NATO Naval Operations. It is an extremely
high worst case environment, which considers average as well as peak levels. It is a very modern
environment, which will probably include the latest status of transmitter development and transmitter
installation. It is not absolutely clear, where this environment will be applied to, but it is very likely, that
weapon systems including EEDs will be considered. - Another environment to be applied for weapon systems
equipped with EEDs is defined in STANAG 4234. It is significantly smaller, but it will probably updated in
the version, which is in preparation (not available for industry).
A modern environment for weapon systems including EEDs and naval applications is also defined in
MIL-STD-464. This environment, however, is significantly smaller than this of the STANAG 1307. – MIL-
STD-464 includes also data about (different) environments for military naval aircraft, space and launch
vehicle systems, ground systems and other applications. The last one will probably include airforce aircraft.
Different environments are available for certification of commercial aircraft and helicopters.
Reduction of risks :
Safety of modern systems can directly depend on the HIRF environment requirements. There are, however,
several different requirements for similar applications, which differ very much. An analysis should be
performed about the reasons for these differences.
 81

Many systems, which are still in use, are hardened on the basis of the older electromagnetic environments, for
example missiles, etc. These environments have been significantly lower and have often considered only
average levels and not the extremely higher peak levels. If the environment has increased like pointed out in
STANAG 1307, there should be a potential risk to different systems. An analysis should be performed about
the systems which are affected and the transmitters, which are the drivers for increase of the environment to
identify the potential risks. – There is probably not a direct risk for the EED-circuits, because sufficient safety
margin should be available, but there can be a high risk for the electronic involved, especially to those
susceptible to peak levels (e.g. computers).
Reduction of effort :
Hardening against the very high HIRF levels and demonstration of sufficient protection is very expensive. Up
to now only one worst case environment is defined by STANAG 1307, which will probably be mainly applied
for weapon systems equipped with EEDs.
Other environments like already started in MIL-STD-464, however, are necessary, too.
The levels should be tailored to the systems affected.
To reduce effort significantly without any reduction of safety, the environments can also split up similar to
what has done for commercial aircraft. A high environment has been defined, which will guarantee safety and
which will only be applied to the safety critical functions. Lower environments will be taken as a basis for
essential functions, that means there is a risk of occasional interference.
Requirements on equipment
Special HIRF requirements on equipment are generally included in the EMC standards/specifications applied
for achieving “Intra-System EMC”.
There are two special tests to represent also the HIRF requirements, the bulk current injection test and the
radiated susceptibility test. In both cases the HIRF requirements will be covered by increased limits.
Relevant requirements are laid down in the MIL-STD-461D/462D and probably also in the STANAG 3516
after the next edition. It is not known, which requirements are on equipment of ships in this case.
Reduction of risk :
Although the MIL-STD-461D/462D is a very new edition, there is a large conflict between the requirements
on equipment and the environment requirements laid down in the STANAG 1307 and also in the MIL-STD-
464. – The levels, required for example for external stores of aircraft are only 200 V/m, while the
requirements of the environment is up to 1270 V/m average and 6680 V/m peak. A similar situation can be
found for equipment mounted on the surface of ships.
It seems to be necessary to tailor the equipment requirements more to the environment requirements,
especially in these cases, where protection on system levels can not be realized (e.g. equipment mounted in
cockpit areas of aircraft).
Reduction of effort :
What has already been mentioned in the relevant chapter of Intra-System EMC is, that the test with respect to
radiated susceptibility can be started at 100 MHz instead of 10 kHz.
Generation just of the very high HIRF fields is extremely expensive because powerful generators are required.
New techniques should be considered, which allow generation of high fields with not too much effort. Of
interest in this case is the “Mode Stirring Camber”, which is already recommended for qualification of
commercial aircraft equipment. – There might be some limitations for equipment with a long reaction time.
This, however, is just under investigation.

Requirements on system
The STANAG 4238 is in preparation for weapon systems equipped with EEDs. Some requirements are also
included in MIL-STD-1385B, which has been replaced meanwhile by MIL-STD-464. – In principle the same
is applicable like already mentioned for Intra-System EMC. Responsible is the system manufacturer, his
interface to the purchaser is the demonstration of sufficient hardening.

System test procedures

System testing is absolutely necessary. – To produce the extreme high field strength levels as far fields across
the whole frequency range in very small frequency intervals, however, requires extreme effort. In general
substitution methods will be applied with transfer function and re-injection techniques.
In practice the situation is similar to the Intra-System EMC. The tests will be performed by test houses, which
have some experience available. The methods and means applied, however, differ, too.
82

It seems necessary in this case, to define agreed test procedures, too. A very helpful basis are the substitution
procedures defined in the HIRF Certification Document for commercial aircraft. The methods included in this
document, cannot only be applied to aircraft.
Some effort can be solved, for example for aircraft, if the tests are coordinated with lightning tests. The test
set-up for clearance in the lower frequency range is, for example, the same like for lightning current injection.

Maintenance
STANAG 7130 (in preparation) will probably cover this problem. The same is applicable like for Intra-
System EMC. Care should be taken about the fact, that this problem is also in discussion for the commercial
aircraft for HIRF and Lightning Protection.- Some more guide might be included in the “User`s Guide” in
preparation for lightning protection.
Modifications
The same is applicable like for Intra-System EMC. Some first rules are defined in the HIRF Certification
Document. – This problem should also be covered by STANAG 7130.

4.2.3 Lightning Protection

The situation with respect to lightning protection can be taken out of table 3-3.
Environment
The lightning environment is covered in STANAG 4236. The latest edition does not cover the full lightning
threat in accordance with the knowledge of today. The Multiple Burst and the E-field threat, for example, is
not included. – The document, however, is in the status of rework. The author is member of the relevant
EUROCAE committee, that means the next edition will probably cover the complete lightning environment
like defined today for aircraft.
MIL-STD-464 already includes the full threat. It has been taken over from the commercial aircraft documents
ED84/SAE ARP 5412.
Good environment data for ground stations can be found in IEC 61024-1/2.
Reduction of risk :
Some aircraft accidents, which have happened in the last years, gave indications, that the action integral and
the charge of the lightning threat like defined for aircraft today, should be increased.
This is partly already proposed in the new edition of STANAG 4236. The threat levels defined, however, are
still below the levels of IEC for ground facilities.
For systems, which require a very high degree of protection, an additional higher threat should be defined.
Requirements on Equipment
Requirements will probably be included in the STANAGs 4236 and 4327. Both are not available to industry.
They seem to cover most systems including weapon systems equipped with EEDs.
Similar techniques will probably applied like defined internationally in the relevant EUROCAE and SAE
committees (author member of EUROCAE committee), that means, there shouldn`t be any problem or risk.
MIL-STD-1512 defines some requirements on EEDs installed in circuits on the ground.
Requirements on equipment are also defined for equipment on the ground in IEC 61312-4.
Reduction of effort :
Reduction of effort might be in some cases possible by limitation of requirements to selected functions only
(e.g. safety critical ones).
In addition reduction might similar to Intra-System EMC be achieved by application of commercial airborne
or ground based equipment.

Requirements on system
STANAG 4238 (in preparation, not available to industry) might also cover lightning protection for munitions
and weapon systems including EEDs. - STANAG 3559 defines some requirements, also applicable with
respect to lightning protection, but only for metallic aircraft. – The MIL-STD-1795A applicable for aircraft,
shall be replaced by commercial aircraft documents as soon as they are available.
The situation is similar to Intra-System EMC and HIRF. The system manufacturer is generally responsible for
design. The result will be demonstrated by test.
In spite of this it might be very helpful to consider the relevant IEC documents applicable for protection of
ground facilities.
System test procedures
No tests procedures are available up to now on the military side. Some will probably be included in STANAG
4327, the STANAG 7116 for aircraft is in a planning status, which might cover lightning protection, too.
 83

The situation today is, that system tests will be performed by different test houses, sometimes applying
different test methods.
The only document, which will be available soon, is the Testing Standard in preparation by SAE/EUROCAE
for commercial aircraft.
The main points of this document should be taken over by STANAG 7116, if lightning tests should be
covered there.
Maintenance
The same is applicable like for Intra-System EMC and HIRF. Lightning protection of systems might be
influenced by corrosion, age, etc. STANAG 7130 is in a planning status.
Some information will probably available in the “User`s Guide” in preparation for commercial aircraft.
IEC 61024-2 handles methods for ground facilities.

Modifications
Modifications on structure, wiring, installation of additional equipment, etc. may change the lightning
protection situation, too.
Rules have to be defined, how to proceed without repeating expensive tests after each modification. They
might be included in STANAG 7130. Some information about change of electronic etc. can be found in ED
81 / SAE AE 4L-87-3.

4.2.4 Electromagnetic Pulse (EMP)

A summary about the documents available is shown in table 3.-4.
Environment:
The Exo-EMP seems to be defined very well in STANAG 4145 and MIL-STD 2119.
The old 5ns-Puls can be found in MIL-STD-464 and in IEC 61000-2-9/10.

Requirements on equipment
They might be included in STANAG 4145.
They are included in MIL-STD-461D/462D in the test CS 116 (conducted signals) and RS 105 (radiated
signals).
IEC specifies some requirements for protection devices.

Reduction of risk :
The limits specified for CS 116 are 5 A (Airforce) respectively 10 A (Army, Navy) only for the maximum
levels to be injected. These levels might in many cases be too weak.

Requirement on systems
STANAG 4145 might include some requirements. IEC 61 000-5-3/4/5 defines some rules how to protect
commercial systems on ground.
MIL-STD-188-125 A presents design requirements for C4 ground systems.
In principle it is the same situation like for Intra-System EMC, HIRF and Lightning Protection. The system
designer is responsible for sufficient hardening, which has generally to be demonstrated by system testing.

System test procedures

Sufficient system hardening will - similar to the other EM effects discussed up to now –generally be
demonstrated by test houses with a lot of experience in this field. Nevertheless it seems to be very helpful, if
some general test procedures would be described, which include all experience collected up to now.

Maintenance and modifications

The same is applicable like for the other EM effects. STANAG 7130 (in preparation) should probably cover
this field, too.

4.2.5 E- and P-Static

Table 3.-5 presents a survey about what is available.
Environment
On the military side environment requirements have only be defined for EEDs respectively weapon
systems including these components. Two possible sources of charge are considered, the personnel source and
a possible contact to aircraft/helicopters/other systems during transport.
84

On the commercial side are also requirements on electronic equipment. Only a personnel source is
considered, which is, however different (weaker requirement) to the military one.
Requirements on equipment
On the military side are only requirements on EEDs and weapon systems with EEDs. The commercial
side handles commercial electronic equipment.
Reduction of risk :
It might be helpful in many cases to have an E-Static test for military electronic equipment, too. It
might be of special interest for computers, etc.
Requirements on system
STANAG 4434 defines some requirements on packing of susceptible loads. STANAG 3659 includes
some bonding requirements, which will also help to avoid E-Static effects.
IEC 61087 handles charged surfaces, IEC 61340-4-1 floor covering.
System test procedures
STANAG 4239 covers EED/weapon testing, the planned STANAG 7116 might also cover system
testing. – Some ideas of charging up a whole aircraft are included in MIL-STD-464.
Maintenance and modifications
Some guide should be included in STANAG 7130 (in planning status).

4.2.6 High Power Microwaves (HPM)

Nothing is officially available now with respect to HPM. Due to the existing future risk, however, some work
should be started.

4.3 Summary of Most Important Improvements

A summary of the most important improvements is presented in table 4.-1 for Intra-System EMC and HIRF
and in table 4.-2 for Lightning Protection, EMP, E-Static and HPM.
 Definition of Requirements on Requirements on System Rest Maintenance Modification
Environment Equipment Systems Procedures Procedures Procedures
- Test effort for Existing requirements Agreed system test Maintenance Modification
expensive radiated should also consider procedures should be procedures shall be procedures shall be
susceptibility tests new materials available available available
Intra-System n.a. can be reduced (for a/c in (in preparation) (in preparation ?)
EMC - Commercial preparation?)
equipment might be
applied (especially
ground systems)
- New procedures for
Modular Avionic in
Future

- Risk analysis - Test effort for Existing requirements Agreed system test Maintenance Modification
required for use of expensive radiated should also consider procedures should be procedures shall be procedures shall be
older systems susceptibility tests new materials available available available
HIRF - Analysis and can be reduced (for a/c in (in preparation) (in preparation ?)
harmonization of - New test methods preparation?)
different should be con- (for commercial
environments sidered aircraft available)
required - Limits sometimes
- Environments not in line with new
depending on environment
criticality mmay help requirements
to save effort.

Table 4.-1 : Summary of Most Important Results, Intra-System EMC and HIRF

85
 86
Definition of Requirements on Requirements on System Rest Maintenance Modification
Environment Equipment Systems Procedures Procedures Procedures
- Not sufficient now; Available for Existing Agreed system test Maintenance Modification
probably sufficient commercial a/c. requirements should procedures should be procedures shall be procedures shall be
in next documents Will probably be also consider new available available available
Lightning Protection - Safety critical taken over for in materials Probably included for (in preparation) (in preparation ?)
applications might new STANAG. different systems in
require higher levels (seem not to be new STANAG.
that defined for a/c foreseen for a/c) (for military a/c in
today (probably preparation? ; soon
partly realized in available for
new documents commercial a/c)

Limits seem Agreed system test Maintenance Modification

sometimes too low procedures should be procedures shall be procedures shall be
EMP ok available available available
(for military a/c in (in preparation) (in preparation ?)
preparation?)
Test for equipment Maintenance
E-Static should be available procedures shall be
(“EN, IEC”) available
(in preparation)
HPM Nothing available Nothing available Nothing available Nothing available Nothing available Nothing available

Table 4.-2 : Summary of Most Important Results, Lightning Protection, EMP and E-Stat
 87

5. RISKS IN EMC OF FUTURE SYSTEMS

The integration of equipment into systems from the point of view of designing for EMC can traditionally be
considered from a number of points of view:

• Ensuring that a number of equipment, when connected together to provide a system function, will
operate as designed without interfering with each other or being susceptible to the
electromagnetic environment in which the systems is immersed.
• Ensuring that a number of separate system functions, when co-located, often in close proximity
within a vehicle, will operate as designed without interfering with each other or being susceptible
to the electromagnetic environment in which the systems is immersed.
• Ensuring that a complete military system (e.g. tank, missile, aircraft or ship) can operate with
other systems in the battle space as designed without interfering with each other or being
susceptible to the electromagnetic environment in which the systems is immersed.

At all levels of integration there is wide commonality of the considerations to be taken when designing for
EMC, these include:

At the level of the platform operating in the battlefield:

• The electromagnetic emissions (intentional and unintentional) produced by the complete system
and their impact on the battlefield in which they will operate co-operatively with other complex
systems and the susceptibility of the complete system to the electromagnetic environment of the
battle space (including both natural and man-made environments).

At level of the complete weapon system:

• The electrical design of the containing shell (e.g. rack, vehicle chassis, airframe etc.) in terms of
bonding, material usage and topology in order to create a desired internal, electromagnetic
environment in which the sensitive electronics are contained, when the platform is immersed in an
external environment.
• System architecture in terms of signalling level and type versus cable length and environment and
the design of cable systems in terms of formats (e.g. twisted or coax), shielding, termination
(particularly of the shields) and routing to complement that systems architecture.

At the level of the equipment which contains the sensitive electronics:

• The design of the interface circuitry (e.g. filtering and format) between the sensitive electronics
and the interconnections to the rest of the system and the electromagnetic design of the
containment system.
• The design of the printed circuit boards (PCBs), which provide the inter-connections between the
components, to ensure freedom from internal interference for all operating modes of the
equipment.

Although the varieties of considerations have been quoted separately there are balances to be struck between
all considerations and it can be seen that EMC is a significant integration concern for complex systems.

5.1. Risk Analysis.

It is anticipated that the risks in designing for EMC will increase unless research & development (R&D) is
carried out to address these risks. Risks will arise in a number of ways, namely:

• Increases in existing known risks as a result of tighter commercial pressures arising from
competition.
88

• Technological change.
• Tighter requirements from customers.

It is well understood that unless investment in R&D is made risks will increase, even in the absence of new
technology or requirements, because of the continually changing world. This part of the report considers the
likely risks that must be addressed and a mitigation strategy is proposed.

First of all a list of risks must be created and then each risk must be examined in more detail to determine the
impact, the likelihood of occurrence and a possible mitigation strategy. It is worth dividing the risks into one
of three groups depending on the cause as outlined above.

5.1.1. Commercially driven risk

(a) The true electromagnetic behaviour can only be judged when the complete system under consideration is
assembled. This only occurs very late in the programme, making modification in the event of design
failure very expensive. Fixed price procurement makes late discovery of problems totally unacceptable.

(b) The high power facilities required to demonstrate ultimate performance are a rare resource and are
required to be reserved well in advance and that date MUST be kept. This is a considerable risk in a long
complex programme. The various test establishments presently available in the Western World, usually
financed by National Governments are being closed or “privatised”. This will ultimately result in
significant competition for time in the remaining facilities. Such time will become “fixed points” in the
programme.

(c) There is considerable pressure to use “commercial-off-the-shelf” (COTS) equipment in military systems.
This equipment is unlikely to have qualification evidence or even be designed to meet the military
electromagnetic environment as required at present. This becomes of even greater concern in the case of
increased requirements in the environment of the future (e.g. Directed Energy Weapons (DEW)).

5.1.2. Technologically driven risk

(d) There is a growing trend in military and commercial systems for the level of integration to be taken to a
more fundamental level (e.g. integrated modular avionics (IMA) in the aircraft business). In such cases
circuit boards or modules at least will be required to operate in close proximity within a rack or frame and
be capable of being relocated or changed regularly through service life without re-testing. In this case the
definition of an “equipment” has changed. Furthermore the electrical and mechanical interface between
these new equipment and the systems into which they are to be integrated has also changed.

(e) In all weapon systems, the use of using electromechanical power instead of hydraulics or mechanical
power is increasing. This places very high current conductors in close proximity to low current/voltage
critical signal cables. This increases the risks associated with systems integration from an EMC point of
view.

(f) A lack of precision in the definition of the external (see Section 5) and internal environment in which the
system is immersed inside the vehicle leads to sub-optimal protection design. In some ways it is
impossible to provide a precise definition, however, a lack of knowledge about the statistics of the
environment experienced in service life, leads to the environment being defined in a deterministic way. It
may be more appropriate for the environment to be defined in a stochastic manner (c.f. reliability). The
EMC performance would then be quoted in a similar manner.

(g) The disparity between the results obtained from tests on part of the system in the qualification laboratory
and the results achieved when the entire system is integrated is an issue that if improved would bring
enormous qualification benefits.
 89

(h) There is a lack of detailed knowledge about the out-of-band behaviour of the components that comprise
the system and particularly the equipment. This increases the risk of equipment and system design for
EMC. Although proven modelling tools for PCB design have yet to emerge, with or without component
behavioural models.

(i) The growing use of electrically complex materials in the structures of platforms makes the integration of
the systems within the structure more difficult. Furthermore, ensuring the correct electromagnetic
performance of the structure becomes a strongly multi-disciplinary design issue.

(j) There will be considerable design conflict in the future associated with meeting the requirements for
antenna installed performance and other performance constraints such as low observability.

(k) There is a trend towards the use of conformal or suppressed antennas. These involve considerable
installed performance modelling challenges

5.1.3. Customer Requirement Driven Risks.

(l) As the external environment requirements become harsher the costs associated with the qualification of
the whole system rise dramatically. New qualification techniques, which avoid the enormous power
requirements and therefore the costs, must be examined.

(m) At present the weapon systems are qualified on a type approval basis just prior to entry into service. There
is no attempt to check the continued EMC performance during service life. This situation cannot continue
and the customer will demand either guarantee (which may be impossible to give) or some form of
maintenance and assurance programme for the continued EMC performance. This is a new challenge to
EMC engineers.

(n) The potential for economically producing malicious electromagnetic threats is growing. The customer is
likely in future to include such threats in the requirements and these will focus attention on EMC
performance because the probability of intercept with such threats must be considered to be unity. Present
EMC requirements, although not quoted, are known to have a low probability of intercept.

5.2 Specific considerations for safety related systems

Applying the EMC Directive to large systems can cause a lot of problems in practice, especially for large
industrial machines. The new guidance document on the application of the EMC Directive is suggesting some
ideas for solving this problems, but gives no practical procedure to be followed. Because a lot of manufac-
turers of large industrial machinery recognized these problems from the early stage for complying with the
EMC Directive, an 'ad hoc' task force within their professional association in Belgium has worked out a
procedure for applying the EMC Directive in practice for large systems. This procedure will be presented and
discussed in this paper.
This procedure applies to large industrial machines, which can be characterised by the fact that it causes a
problem to perform EMC testing under normal laboratory conditions, due to large weight , big size, transpor-
tation problems and access to a laboratory, time needed to build-up the machine, ...
Testing of the whole machine, as well as of the separate units called Electronic Sub-Assemblies (ESA) are
considered within this procedure, which is mainly based on the limits and requirements set by the generic
standards on EMC, but refers also to the EMC requirements set by the Machine Directive.

Introduction. - The procedure which is discussed in this paper, has been worked out in order to be applied as a
means to achieve the conformity with the essential requirements of the European EMC Directive (89/336) and
the EMC requirements of the European Machine Directive (89/392).
90

The procedure applies to the electromagnetic compatibility of large, industrial machines, which can be
characterised by the fact that it causes a problem to perform EMC testing under normal laboratory conditions.
This can be due to:
* large weight
* big size and dimensions
* transportation problems and access to a laboratory
* time needed to build-up the machine
* power consumption
* auxiliary equipment and installations needed
* other ...

Electrical/electronic sub-assemblies or ESA's (as separate technical units) intended for fitment in these
machines are also within the scope ot this procedure. This allows a very easy handling of extra tools and op-
tions, when added to the standard machine.
The procedure describes the requirements on EMC (European Directive 89/336 on EMC) and the related
safety requirements (European Directive 89/392 on Machines), and the procedures necessary for testing. The
following disturbance phenomena are dealt with:
* electromagnetic interference by emission
* eletromagnetic field immunity
* current injecting immunity
* LF-magnetic field immunity (if applicable)
* electrostatic discharge (ESD)
* conducted transients
* voltage fluctuations, dips and interruptions
* harmonics and flicker

In the next sections, requirements and testing methods will be discussed in more detail.

Requirements.

General requirements.
It is important to mention here that a product is covered by the Directives, if it is in the field of application and
presents potential hazrads with respect to EMC. This means that it should be contemplated in one or more
essential safety and/or protection requirements, and for which a protective action is justified. This is an
exclusive manufacturers decision. The manufacturer is the only and ultimate responsible for the conformity of
this product to the directive. Furthermore, he is the only one able to evaluate the hazards that the product may
or will present when used as intended. He will do such evaluation by the way of a hazard analysis or risk
analysis, that, once done, will allow him to decide which specific parts of the machine or ESA's should be
tested and for which specific requirements, and at which level of severity.

Fulfillment of the requirements.

The requirements of this procedure are deemed to be fulfilled, when:
* the complete machine fulfills the general requirements. In this case, no routine tests of the ESA's are
requested.
* all ESA's are fulfilling their specific requirements, and when they are properly installed, in conformance
with their recommended installation procedures.
* the machine has no such equipment for which an interference or immunity test is required.

Testing.
It is chosen for a kind of "type testing" as test procedure. Due to this choice, tightened limit values apply for
the radiating tests, in order to account for insignificant differences between the test specimen and the series
product, and for the repeatiblity and reproducibility of the test rresults themselves.
This choice means also that the reference limits are taken as a basis for a hundred percent testing of the
production and for inspection.
 91

If the machine is part of a larger system, or can be connected to auxiliary apparatus, then the machine will be
tested while connected to the minimum representative configuration.

Specific rules for Immunity testing.

Referring to the hazard or risk analysis, no disturbances shall occur during the testing which may affect the
safety of the machine: it concerns movements of parts of the machine and modifications on the state of
function which may generate hazards or mislead others. For this functions, performance criterium A must be
achieved, as this criterium is defined in the generic EMC standards for immunity testing (EN 50082-1/2).
For the other essential functions of the machine, they should comply with the performance rrequirements as
set by the manufacturer.

All tests shall be performed in the most susceptible operating mode in the frequency bands being investigated
consistent with normal applications. The configuration of the test sample shall be varied to achieve the
maximum susceptibility (Worst Case Configuration), following the results from the hazard or risk analysis.

It may be determined from considerations of the hazard analysis and/or of the electrical characteristics and
usage of a particular machine or ESA that some of the measurements or tests are inappropriate and therefor
unnecessary. In such case, it will be required that the decision no to test is recorded in the test report.

Emission measurements.
At the level of the machine, the measurements are performed 'in situ'. Referring to ongoing EN proposals and
amendments, no groundplane should be applied.

In order to reduce the test-time, the following method is used for continuous noise:
- first, a measurement is performed using PD. If the measured values are lower than the QPD limits, the
machine will comply.
- if the PD measured values are exceeding the QPD limits, a QPD measurement is peformed only at these
frequencies.

conducted emission.
For conducted emission testing, a LISN should be used complying with EN 55011 requirements. In case of a
3-phase main power system, the method is also applicable phase per phase. In order to avoid dammage of the
LISN from the in-rush currents of the machine, a special shunt-circuit can be used. In cases of high current, a
1500/50 Ohm probe (as referred in EN 55011) may be used, either in a single phase/three phase version.
When it is impossible to perform voltage disturbance measurements, the common mode currents of the main
power supply can be measured, using appropriate current clamps or current probes.

The procedure provides limits for both disturbance voltages or disturbance common mode current, in function
of the mains input current. Three levels of limits are given, based on a division of the input current as:
- lower than 25 A
- between 25 A and 100 A
- over 100 A

The limits are based on other proposed EN standards. The rationale for the different limit levels is due to the
fact that in industrial environments, machines which have a high current or power consumption, will also be
connected onto an own transformer station. In this way, higher conducted interference levels can be allowed,
as long as the own plant is not disturbed.

radiated emission.
For radiated emission testing, limit levels are provided for 3 measuring distances, namely 30m, 10m and 3m.
It is evident that for in situ measurements, 30m measuring distance cannot be used, because or normal rather
high background levels. Preferably, the ambient noise shculd be at least 6 dB less than the radiated noise of
the machine under test.
92

Therefor, an appropriate procedure should be applied for discrimination between ambient noise and radiated
emission by the machine under test. The method used herefor and its rationale must be reported in the test
report.
As an example, a method is reported, where the machine under test is switched on/switched off, so that at the
specific frequencies to be controlled, a momentaneous discrimination between machine and ambient noise can
be performed.
In case there are no other possibilities, a measuring distance as close as to 1m is acceptable, using a correction
factor of 20 log(Ds/Dm). For this method, it is referred to a French Telecom Standard (ref. 112-30), where a
measuring distance of 1m is used for in situ measurements of telecom equipment at the customer premisses.

At least 4 measuring points around the machine must be tested. The position of the test points, and also the
exact number of measuring points, are defined by the former hazard analysis. At least one antenna height of
1.5m is used. Other (fixed) antenna heights may be used, depending again from the former hazard analysis,
showing the locations with the highest emission levels.

specifications concerning ESA's.

If the way of ESA testing is used, the specific harmonised European standards must be applied for the type of
ESA under consideration. Examples are the specific European standards for PLC's (programmable
controlllers) and for frequency convertors. If no specific standard is available, the above method and
procedure should be used.

Harmonics and flicker.

For harmonics and flicker, it is referred to the EN61000-3 series of standards and proposed standards.

Immunity testing.
At the level of the machine, the tests are performed 'in situ', when technical possible and performed in such
way, that there is no risk for other apparatus, equipment or installations.

For functions concerning the safety of the machine, the performance criteria A as set in this procedure must be
considered as minimum recommended requirements. They can be more severe, depending on the outcome of
the hazard analysis.
For the functions of the machine, the mentioned requirements must be considered as normal recommended
requirements.

ESD.
For ESD, the safety requirements are set a 15 kV air discharge severity level with a performance criterium A,
where for the normal functions only 8 kV with a criterium B is required.

Radiated immunity.
10 V/m field strength is required for all cases.
A uniform field distribution is not required: an uniform field can not always be achieved for these types of
large machines. Following the outcome of the hazard or risk analysis, the field strength must be obtained at
the location of the specific part under test.
25 % field strength is added for type testing.

EFT.
Depending on both safety functions and process control functions of I/O, signal and control lines, both
severity levels and performance criteria are different.
Possible injection methods can be single phase, and using a capacitive clamp (or equivalent capacitor) even
for the main power supply.
The reason is that in many cases, the coupling networks cannot hold the large currents of the machine, or even
that the installation of the machine does not allow to disconnect the main power supply lines, in order to
couple them through the EFT coupling network.
 93

When technically impossible to perform any form of this test on the machine level, the critical ESA's must
comply with the requested requirements.

Surge.
Depending on both safety functions and process control functions of I/O, signal and control lines, both
severity levels and performance criteria are different.
Possible injection methods can be single phase, or another equivalent coupling mechanism.
Because surge is simulating an overvoltage on the lines due to external transients, the hazard or risk analysis
should indicate on which lines a surge test must be performed, if technically possible. Otherwise, the critical
ESA' must comply the requested requirements.
External protection devices, which are required in the installation manual, must be included in the test setup.

Injected current.
The injected current can be applied using coupling networks (CDNs). But due to practical problems, especial-
ly for the main power supply lines, the use of a current injection clamp is accepted.
When technically not possible, the critical ESA's must comply with the requested rrequirements.

Voltage fluctuations, dips & interruptions.

Depending on safety functions or other functions of the machine, the performance criteria required will differ
for the different types of voltage fluctuations, dips and interruptions.
It should also be mentioned again that on the machine level, these tests cannot always be performed, because
of the high current level and/or the impossibility to disconnect the main power lines, in order to pass them
through the test equipment.
Therefor, the critical ESA's must comply with the requirements set for the machine.

Power frequency magnetic fields.

If this test is applicable, ie. when there are magnetic sensitive devices used, a power frequency magnetic field
must be generated at the level of these devices.
When no global test can be performed, or the critical ESA's must comply with the requested requirements.
Another possibility is to use small coils to test locally the different magnetic sensitive devices in the machines.
Small coils are described in the standard EN 55103-2 (EMC for professional audio, video and entertainment
apparatus).

specifications concerning ESA's.

If the way of ESA testing is used, the specific harmonised European standards must be applied for the type of
ESA under consideration. Examples are the specific European standards for PLC's (programmable
controlllers) and for frequency convertors. If no specific standard is available, the above method and
procedure should be used.
94

5.3. Proposals for Risk Reduction.

RISK Impact Likelihood MITIGATION

Commercially Driven Risk

(a) Late risk exposure in a fixed price HIGH MED Improve the capability of modelling and
environment. the relevance of equipment test
techniques
(b) Reducing number of specialist HIGH MED Reduce reliance on specialist high power
facilities for whole system clearance facilities by whole system test technique
development
(c) The introduction of COTS MED HIGH Improved commercial specifications and
equipment into a system with harsh greater design influence in systems
EMC requirements. installation.

Technologically Driven Risk

(d) Electromagnetic Integration of HIGH HIGH Develop module qualification test
IMA techniques.
(e) Electromagnetic Integration of MED MED Development of cable harness design
“more-electric- systems” tools
(f) Stochastic definitions of EMC and MED MED Develop stochastic viewpoint on all
installed antenna performance coupling phenomena
(g) Lack of correlation between MED MED Improve the equipment qualification test
equipment qualification results & techniques.
whole system performance
(h) Out-of-band behaviour of system MED MED Improved access to details of
components and antennas components or place contractual
requirements on provision of mini-
models.
(i) Use of electrically complex HIGH HIGH Develop modelling capabilities which
materials in structures makes the can account for complex materials
integration on to and within the
structure more complex
(j) Conflicts between installed HIGH HIGH Development of installed performance
antenna performance and other models to contribute to multi-
requirements. disciplinary design.
(k) The increased use of suppressed HIGH HIGH As above but with added capability for
or conformal antennas. complex antenna elements.

Requirements Driven Risks

(l) Test cost escalation with HIGH HIGH Develop test & qualification techniques
increasing environment levels which are not heavily reliant on full-
threat testing
(m) Meeting the demand for MED MED Development of reduced cost surveying
production sample testing and in- techniques
service testing
(n) Meeting new threats such as MED MED As in (l) above.
HPM.
 95

6. RECOMMENDATIONS
6.1 Recommendations for developments in modelling techniques
• Development of techniques for coupling different codes applicable to different regimes of the complete
problem
• Definition of validation criteria for EMC modelling codes
• Development of data capture and CAD cleaning processes
• Development of special elements to cater for advanced materials and small but influential details
• Development of PCB modelling tools
• Development of component models
• Development of antenna element models

6.2 Recommendations for developments in test techniques

• Development of guidelines or standard recommended practices for intra-system EMC, HIRF, lightning,
EMP, HPM testing
• Validation of direct current injection techniques and methods using mode-stirred chambers
• Development of integrated test techniques for equipment and systems
• Development of test techniques for in-service and production sample testing for equipment and systems
• Derivation of stochastically based safety margins

6.3 Recommendations for development of standards

• Completion of existing standards
• System test procedures
• Maintenance and modifications
• Application of commercial standards for systems
• Commercial aircraft (lightning + EMC)
• Ground facilities (EN + IEC)
• Updating requirements for equipment to new environments
• New standards for HPM
• New standards for modular avionics
• Reorganization of standards (similar to MIL-464 hierarchy)
• Standardization of electronic formats of equipment qualification data for system use
• Harmonization of different standards in order to avoid repetitions

6.3.1 Development in Published Standards

The tables 3.-1 to 3.-5 present a large number of standards/specifications, all handling Intra-System EMC and
the most important electromagnetic environment effects. – Further standards have to be added, if also
electromagnetic areas would be considered, which have not be included in this report. – The list would be
extended again, if all commercial standards and specifications, which are available, would be mentioned, too.
All the military standards/specifications are needed for military system design and to ensure, that sufficient
protection is guaranteed during life time of the systems.
Some important data (e.g. the environments) or procedures are called up in different documents. Some
documents are based on an older technical standard or status of knowledge, others on newer ones. To avoid
conflicts and also risks, a lot of the existing documents need always be updated and harmonized. The intervals
should not be too long.
In addition, in spite of all the documents available on the military side, it can be seen, there a still some
missing.
Both, to update and harmonize the existing documents and to create new ones, needs a lot of work/effort and a
lot of time.
The way out is to create such as a leading document just for the important field of system development, which
is based on the greatest number of standards to involve more and more this, what is already available to
improve the documents or to fill the leaks. This means mainly the involvement of commercial
96

standards/documents. There are a lot available (see “references”). They have to be analyzed very carefully
with respect to their military applicability. In many cases, however, they might be sufficient.
This way has already be gone by MIL-STD-464, although many things might to be improved.
It presents in a very concentrated way for all systems (airborne, sea, ground, space) a survey of the
requirements with respect to all electromagnetic requirements, starting e.g. at power line transient level up to
EMP protection and TEMPEST. If the requirements are not included in the standard itself, it calls up the
applicable documents. These are not only military ones, but also commercial ones!

Several MIL-STD´s have already been replaced by MIL-STD-464, that means the
- MIL-STD-1818A : “Electromagnetic Effects Requirements for Systems”
- MIL-STD-6051D : “Electromagnetic Requirements, Systems”
- MIL-STD-1385 : “Preclusion of Ordenance Hazards in Electromagnetic Fields; General
Requirements for”
- MIL-B-5087 B : “Bonding, Electrical and Lightning Protection for Aerospace Systems”

In addition, the MIL-STD-464 includes a lot of guide, how to perform protection in the different areas and
which handbooks are available to solve the problems. The actual standard, for example, consists of 16 pages,
the appendices with the guide lines of 95 pages.
Commercial standards will directly replace some MIL-STDs, too.

Important examples are :

- MIL-STD 285 : “Attenuation Measure for Enclosures EM shielding for Electronic Test Purposes,
Method of”
It is replaced by IEEE 299-1991
- MIL-STD 1757 A: “ Lightning Protection for Aerospace Vehicles on Hardware”
It will be replaced by the documents prepared for lightning protection of commercial aircraft as soon as
available.
A lot of MIL-STDs have been cancelled without any replacement or by bringing them down to Handbooks or
Standard Practice documents, that means, there seems to be something like a cleaning-up”-process.
It might be reasonable, if STANAG would follow similar procedures. A document similar to MIL-STD-464
might already be in a planning status with STANAG 4567.

6.4 Recommendations on legacy systems

• Examination of the impact on operational role of increased environment
• Assessment of critical circuit technology in each system
• Recommendations produced on restrictions

It has been pointed out in chapter 3.4.3 of this report, that a new “ High Intensity Radiated Field” environment
has been specified by NATO in STANAG 1307. This environment reflects the higher output power of the
transmitters installed, their new modulations and the new frequency bands taken more and more in use.
This new environment is significantly higher than all environments specified ever in the past. It specifies also
very large amplitude pulse modulated signals, which have been found to be very important for modern digital
electronic equipment.
This environment will be the basis for hardening of all future NATO weapon systems to guarantee safety and
mission performance under all circumstances.
Under the preposition, that this environment reflects the existing situation, problems can not be excluded for
the existing weapon systems which are in use today. They are generally hardened in accordance with older
and weaker specifications. Safety might be affected in this case as well as mission performance.
To avoid any future risks the following procedures are proposed :
- Identification of the transmitters and situations responsible for the significant increase of the new
environment.
- Performance of an analysis, which weapon systems might be affected by these increased levels. - The
basis for a first evaluation should be the assessment of the critical technology installed in the different
systems.
- As a result information is available, which constellations between which weapon systems and transmitters
installed on carriers or outside will probably be critical. These situations can than be avoided e.g. by
restrictions.
 REPORT DOCUMENTATION PAGE
1. Recipient’s Reference 2. Originator’s References 3. Further Reference 4. Security Classification
of Document
RTO-TR-059 ISBN 92-837-1084-3 UNCLASSIFIED/
AC/323(SET-005)TP/22 UNLIMITED
5. Originator Research and Technology Organisation
North Atlantic Treaty Organisation
BP 25, F-92201 Neuilly-sur-Seine Cedex, France
6. Title
Electromagnetic Compatibility in the Defense Systems of Future Years
7. Presented at/sponsored by
the Sensors and Electronics Technology Panel (SET) Working Group WG-01.
8. Author(s)/Editor(s) 9. Date
Multiple June 2002
10. Author’s/Editor’s Address 11. Pages
Multiple 108

12. Distribution Statement There are no restrictions on the distribution of this document.
Information about the availability of this and other RTO
unclassified publications is given on the back cover.
13. Keywords/Descriptors

Airborne equipment Military requirements

Aircraft Models
Antennas Numerical models
Avionics Radiofrequency interference
Commercial equipment Risk analysis
Design Safety engineering
Electromagnetic compatibility Specifications
Electromagnetic interference Standards
Methodology Transmitters

14. Abstract

The study has focussed on three areas of EMC design, development and qualification in future
defence systems, namely:
– Numerical modelling
– Test techniques
– Published standards
The limitations of existing techniques and standards have been examined and highlighted. Such
limitations cause risks at the present time. However, the risks will increase as a result of
changes in the commercial and technological environment and potential increases in risk as a
result of these changes in the absence of research development, have been highlighted.
Furthermore, recommendations on investment in research and development have been made in
order to mitigate the increasing risks.
This page has been deliberately left blank

Page intentionnellement blanche

 NORTH ATLANTIC TREATY ORGANISATION

RESEARCH AND TECHNOLOGY ORGANISATION

BP 25 • 7 RUE ANCELLE DIFFUSION DES PUBLICATIONS

F-92201 NEUILLY-SUR-SEINE CEDEX • FRANCE RTO NON CLASSIFIEES
Télécopie 0(1)55.61.22.99 • E-mail mailbox@rta.nato.int
L’Organisation pour la recherche et la technologie de l’OTAN (RTO), détient un stock limité de certaines de ses publications récentes, ainsi
que de celles de l’ancien AGARD (Groupe consultatif pour la recherche et les réalisations aérospatiales de l’OTAN). Celles-ci pourront
éventuellement être obtenues sous forme de copie papier. Pour de plus amples renseignements concernant l’achat de ces ouvrages,
adressez-vous par lettre ou par télécopie à l’adresse indiquée ci-dessus. Veuillez ne pas téléphoner.
Des exemplaires supplémentaires peuvent parfois être obtenus auprès des centres nationaux de distribution indiqués ci-dessous. Si vous
souhaitez recevoir toutes les publications de la RTO, ou simplement celles qui concernent certains Panels, vous pouvez demander d’être
inclus sur la liste d’envoi de l’un de ces centres.
Les publications de la RTO et de l’AGARD sont en vente auprès des agences de vente indiquées ci-dessous, sous forme de photocopie ou
de microfiche. Certains originaux peuvent également être obtenus auprès de CASI.

CENTRES DE DIFFUSION NATIONAUX

ALLEMAGNE FRANCE PAYS-BAS
Streitkräfteamt / Abteilung III O.N.E.R.A. (ISP) NDRCC
Fachinformationszentrum der 29, Avenue de la Division Leclerc DGM/DWOO
Bundeswehr, (FIZBw) BP 72, 92322 Châtillon Cedex P.O. Box 20701
Friedrich-Ebert-Allee 34 2500 ES Den Haag
D-53113 Bonn GRECE (Correspondant)
Hellenic Ministry of National POLOGNE
BELGIQUE Defence Chief of International Cooperation
Etat-Major de la Défense Defence Industry Research & Division
Département d’Etat-Major Stratégie Technology General Directorate Research & Development Department
ACOS-STRAT-STE – Coord. RTO Technological R&D Directorate 218 Niepodleglosci Av.
Quartier Reine Elisabeth D.Soutsou 40, GR-11521, Athens 00-911 Warsaw
Rue d’Evère, B-1140 Bruxelles
HONGRIE PORTUGAL
CANADA Department for Scientific Estado Maior da Força Aérea
Services d’information scientifique Analysis SDFA - Centro de Documentação
pour la défense (SISD) Institute of Military Technology Alfragide
R et D pour la défense Canada Ministry of Defence P-2720 Amadora
Ministère de la Défense nationale H-1525 Budapest P O Box 26
Ottawa, Ontario K1A 0K2 REPUBLIQUE TCHEQUE
ISLANDE DIC Czech Republic-NATO RTO
DANEMARK Director of Aviation VTÚL a PVO Praha
Danish Defence Research Establishment c/o Flugrad Mladoboleslavská ∨ul.
Ryvangs Allé 1, P.O. Box 2715 Reykjavik Praha 9, 197 06, Ceská republika
DK-2100 Copenhagen Ø ITALIE ROYAUME-UNI
ESPAGNE Centro di Documentazione Dstl Knowledge Services
INTA (RTO/AGARD Publications) Tecnico-Scientifica della Difesa Kentigern House, Room 2246
Carretera de Torrejón a Ajalvir, Pk.4 Via XX Settembre 123a 65 Brown Street
28850 Torrejón de Ardoz - Madrid 00187 Roma Glasgow G2 8EX
ETATS-UNIS LUXEMBOURG TURQUIE
NASA Center for AeroSpace Voir Belgique Millı̂ Savunma Bas,kanli i (MSB)
Information (CASI) NORVEGE ARGE Dairesi Bas,kanli i (MSB)
Parkway Center Norwegian Defence Research 06650 Bakanliklar - Ankara
7121 Standard Drive Establishment
Hanover, MD 21076-1320 Attn: Biblioteket
P.O. Box 25, NO-2007 Kjeller

AGENCES DE VENTE
NASA Center for AeroSpace The British Library Document Canada Institute for Scientific and
Information (CASI) Supply Centre Technical Information (CISTI)
Parkway Center Boston Spa, Wetherby National Research Council
7121 Standard Drive West Yorkshire LS23 7BQ Acquisitions
Hanover, MD 21076-1320 Royaume-Uni Montreal Road, Building M-55
Etats-Unis Ottawa K1A 0S2, Canada
Les demandes de documents RTO ou AGARD doivent comporter la dénomination “RTO” ou “AGARD” selon le cas, suivie du
numéro de série (par exemple AGARD-AG-315). Des informations analogues, telles que le titre et la date de publication sont
souhaitables. Des références bibliographiques complètes ainsi que des résumés des publications RTO et AGARD figurent dans les
journaux suivants:
Scientific and Technical Aerospace Reports (STAR) Government Reports Announcements & Index (GRA&I)
STAR peut être consulté en ligne au localisateur de publié par le National Technical Information Service
ressources uniformes (URL) suivant: Springfield
http://www.sti.nasa.gov/Pubs/star/Star.html Virginia 2216
STAR est édité par CASI dans le cadre du programme Etats-Unis
NASA d’information scientifique et technique (STI) (accessible également en mode interactif dans la base de
STI Program Office, MS 157A données bibliographiques en ligne du NTIS, et sur CD-ROM)
NASA Langley Research Center
Hampton, Virginia 23681-0001
Etats-Unis

Imprimé par Groupe d’imprimerie St-Joseph inc.

(Membre de la Corporation St-Joseph)
1165, rue Kenaston, Ottawa (Ontario), Canada K1G 6S1
 NORTH ATLANTIC TREATY ORGANISATION

RESEARCH AND TECHNOLOGY ORGANISATION

BP 25 • 7 RUE ANCELLE DISTRIBUTION OF UNCLASSIFIED

F-92201 NEUILLY-SUR-SEINE CEDEX • FRANCE RTO PUBLICATIONS
Telefax 0(1)55.61.22.99 • E-mail mailbox@rta.nato.int
NATO’s Research and Technology Organisation (RTO) holds limited quantities of some of its recent publications and those of the former
AGARD (Advisory Group for Aerospace Research & Development of NATO), and these may be available for purchase in hard copy form.
For more information, write or send a telefax to the address given above. Please do not telephone.
Further copies are sometimes available from the National Distribution Centres listed below. If you wish to receive all RTO publications, or
just those relating to one or more specific RTO Panels, they may be willing to include you (or your organisation) in their distribution.
RTO and AGARD publications may be purchased from the Sales Agencies listed below, in photocopy or microfiche form. Original copies
of some publications may be available from CASI.

NATIONAL DISTRIBUTION CENTRES

BELGIUM GREECE (Point of Contact) POLAND
Etat-Major de la Défense Hellenic Ministry of National Chief of International Cooperation
Département d’Etat-Major Stratégie Defence Division
ACOS-STRAT-STE – Coord. RTO Defence Industry Research & Research & Development
Quartier Reine Elisabeth Technology General Directorate Department
Rue d’Evère, B-1140 Bruxelles Technological R&D Directorate 218 Niepodleglosci Av.
D.Soutsou 40, GR-11521, Athens 00-911 Warsaw
CANADA
Defence Scientific Information HUNGARY PORTUGAL
Services (DSIS) Department for Scientific Estado Maior da Força Aérea
Defence R&D Canada Analysis SDFA - Centro de Documentação
Department of National Defence Institute of Military Technology Alfragide
Ottawa, Ontario K1A 0K2 Ministry of Defence P-2720 Amadora
H-1525 Budapest P O Box 26
CZECH REPUBLIC SPAIN
DIC Czech Republic-NATO RTO ICELAND INTA (RTO/AGARD Publications)
VTÚL a PVO Praha Director of Aviation Carretera de Torrejón a Ajalvir, Pk.4
Mladoboleslavská ∨ul. c/o Flugrad 28850 Torrejón de Ardoz - Madrid
Praha 9, 197 06, Ceská republika Reykjavik
TURKEY
DENMARK ITALY Millı̂ Savunma Bas,kanli i (MSB)
Danish Defence Research Centro di Documentazione ARGE Dairesi Bas,kanli i (MSB)
Establishment Tecnico-Scientifica della Difesa 06650 Bakanliklar - Ankara
Ryvangs Allé 1, P.O. Box 2715 Via XX Settembre 123a
DK-2100 Copenhagen Ø 00187 Roma UNITED KINGDOM
Dstl Knowledge Services
FRANCE LUXEMBOURG Kentigern House, Room 2246
O.N.E.R.A. (ISP) See Belgium 65 Brown Street
29 Avenue de la Division Leclerc Glasgow G2 8EX
BP 72, 92322 Châtillon Cedex NETHERLANDS
NDRCC UNITED STATES
GERMANY DGM/DWOO NASA Center for AeroSpace
Streitkräfteamt / Abteilung III P.O. Box 20701 Information (CASI)
Fachinformationszentrum der 2500 ES Den Haag Parkway Center
Bundeswehr, (FIZBw) 7121 Standard Drive
Friedrich-Ebert-Allee 34 NORWAY Hanover, MD 21076-1320
D-53113 Bonn Norwegian Defence Research
Establishment
Attn: Biblioteket
P.O. Box 25, NO-2007 Kjeller

SALES AGENCIES
NASA Center for AeroSpace The British Library Document Canada Institute for Scientific and
Information (CASI) Supply Centre Technical Information (CISTI)
Parkway Center Boston Spa, Wetherby National Research Council
7121 Standard Drive West Yorkshire LS23 7BQ Acquisitions
Hanover, MD 21076-1320 United Kingdom Montreal Road, Building M-55
United States Ottawa K1A 0S2, Canada
Requests for RTO or AGARD documents should include the word ‘RTO’ or ‘AGARD’, as appropriate, followed by the serial
number (for example AGARD-AG-315). Collateral information such as title and publication date is desirable. Full bibliographical
references and abstracts of RTO and AGARD publications are given in the following journals:
Scientific and Technical Aerospace Reports (STAR) Government Reports Announcements & Index (GRA&I)
STAR is available on-line at the following uniform published by the National Technical Information Service
resource locator: Springfield
http://www.sti.nasa.gov/Pubs/star/Star.html Virginia 22161
STAR is published by CASI for the NASA Scientific United States
and Technical Information (STI) Program (also available online in the NTIS Bibliographic
STI Program Office, MS 157A Database or on CD-ROM)
NASA Langley Research Center
Hampton, Virginia 23681-0001
United States

Printed by St. Joseph Print Group Inc.

(A St. Joseph Corporation Company)
1165 Kenaston Street, Ottawa, Ontario, Canada K1G 6S1

ISBN 92-837-1084-3