Mini UAVs Detection by Radar
Miroslav Krátký*, Luboš Fuxa†
* University of Defence, Kounicova 65, Czech Republic, e-mail: Miroslav.Kratky@unob.cz
†
University of Defence, Kounicova 65, Czech Republic, e-mail: Lubos.Fuxa@unob.cz
Abstract—The issues of using, and in recent time misusing of From the defence against UAVs point of view there is
unmanned aerial vehicles is becoming the hot & topical problem. a need to calculate with several specifics: structural, flight,
This paper deals with possible ways their detection, especially tactic of employment etc. The terminology Low, Small and
within the radar frequency spectrum. Slow (LSS) target is used in some works – and this is the point
epitomize UAVs as the air threat.
Keywords: UAV; LSS, Air-defence; Radar; Infrared, Acoustic,
Reconnaissance, Terrorism Hence, the philosophy of defence against them should be
formed, taking these specifics into account. The possible ways
I. INTRODUCTION of UVAs’ elimination in principles are based on standard air-
Means of Air Attack (MoAA) were, they are, and they will defence measures (in detail [3]). But these measures should be
in the future the inseparable part all modern armed conflicts. modifies in some aspects. The chain of MoAA elimination
That goes always, when warring parties have the MoAA in consists of three basic phases: reconnaissance Æ command &
disposal. Highly developed armies are using the whole control (C2) Æ elimination; (detailed: detection – recognition –
spectrum of MoAA, and their quantity, employment intensity identification – localisation Æ data fusion & processing – fire
and proportion among them depend on row of factors: decision Æ elimination). For engagement MoAA categories
“mini” and “micro” UAVs1 the chain has several difficulties,
• Disposition and situation of enemy; namely in phases detection and elimination.
• Type of operation; From the above outlined multi-discipline problems, this
• Phase of conflict; paper deals with certain aspects of mini UAVs detection only.
Presented results proceed from research at Department of air-
• Local conditions of the operation;
defence systems, University of Defence Brno, including
• Mandates given to the Air Forces; experiments.
• etc.
II. UAVS’ RECONNAISSANCE
Oftentimes, there are next – non-military factors (political,
Air surveillance, which output is the target tracking and its
economic, humanitarian, religious...) too.
parameters are continually transmitting to the C2 system, is
The MoAA categories rate within the conflicts has been realized in the four phases2:
developing historically too, and particularly in the conflicts
1. Detection is a process, when we find with certain
waged in the second half of 20th century the Unmanned Aerial
probability that there is an object in the airspace. This
Vehicles (UAVs) are employed more and more frequently. The
object could be a target (presupposed MoAA) and it
reason is that they have some specific combat capabilities
requires further processing. In practise, this means
(mainly flight performance). The significant positive of their
a target shift to the target monitoring system (so called
deployment is protection of human crew within the hostile and
“Scan” have been performed).
dangerous environment. Sometimes, in the common language,
the UAVs are called “Drones”. 2. Recognition. We understand it as a matching the
object to the determinate category of MoAA, and
Accordingly to the UAVs’ accessibility and construction
according this assignment the subsequent procedures
components’ dynamic price decrease these aircraft are not
are chosen. Usually, already in this phase the
more only domain of developed armies and state safety sector.
preliminary decision for detail processing and
They are accessible practically for anybody and anywhere.
assignment is done.
They could be misused by terrorists’ bodies, both within the
unstable countries territory or in the middle of Europe. The 3. Identification is the output, which defines
same goes for probable enemies’ forces in all type of unambiguously affiliation, type, priority level and
operations and phase of conflicts. additional characteristics. Nevertheless, even the object
is negatively identified as “target” it is kept being
The significant aspect characterizing the danger of
processed and tracked by airspace control authorities.
deployment these small, relatively cheap and without
a demanding training engage-able MoAA against well-
equipped opponents (including NATO) inheres in the
possibility of their mass and multiple employment. 1
For more detailed categorisation – see e.g. in [5].
2
The first three ones are application of the „Johnson’ criterion“, especially
applicable for optical reconnaissance.
4. The outputs of localisation are coordinates of the
target and their derivatives (so called “Track”). Target
is passed to the engagement.
The above described process is, in practice, question of
several seconds, where phases recognition and identification
often are blending (thanks to use system “IFF” - Identification
Friend or Foe). Within the Air force system architecture C2 all
above described phases and their operation run nearly parallel
and in a real time. This is so, because C2 entities are designed
as interconnected components for reconnaissance and fire Figure 1: Radar Band vs. Target Distance
control. The whole system is called “C4ISR” (Command,
Control, Communications, Computers, Intelligence, The figure above does not say in which band is possible, or
Surveillance and Reconnaissance). impossible to detect certain object (having certain RCS).
Particularly influence of atmosphere to the high frequency
For airspace reconnaissance we can use sensors working in
energy propagation is taken into account. The standard
particular part of frequency spectrum with wavelength “λ“: requested parameters of the output signal (accuracy) needed for
• Radars (now standardly λ ∈ 0.1 m - 1.67 cm), further processing and following engagement by active air
defence means is considered.
• Optical sensors - visible (λ ∈ <380 – 750> nm), or
invisible (λ ∈ <0.75 – 5> and <8 - 15>μm) part of In relation to MoAA of “mini UAV” category, radars
spectrum, working at “X” band3 appear to be suitable means - in the view
of mini UAVs’ dimensions and thus their equivalent RCS.
• Acoustic sensors, Such radars offer satisfactory accuracy for measurement of
coordinates (tenths percentage of range) and sufficiently small
• Laser radars („LIDAR“).
antennas dimensions. Technically, there is a possibility to use
As much for airspace surveillance in general as for UAVs’ the “C” band4 too. But there are problems due to occupancy
detection specifically, the radar surveillance means remain the this band by commercial facilities in Czech Republic. It is
primary sources of information in the predictable future. The predictable, that the exploitation of the shorter wave length
significance of optical, acoustic and laser sensors will be rise – bands will be possible when technology allow it. From the
according to technology development. mobility point of view, radar depicted for UAVs detection
should be on mobile or at minimum on easy relocateable
Even though, or just for this, that the sensors detection platform. This is the reason for smallish antennas and
range will increase only slowly and insufficiently in the future, corresponding λ.
there is a need to find another solutions. The possible way is
connect them into the linked, complex surveillance system. The atmospheric effects impact to the high frequency
Their mutual interconnection, interoperability and modularity energy propagation here is still compensateable. The reason is,
should lead to synergic effects reside at minimum in detection that for category MoAA “mini UAV” and suchlike ones, will
probability rise and false alarms reduction. be probably employed according to specific tactics policy and
their range of reconnaissance is supposed to be at distances
Taking into consideration the complexity of detection from several units up to few tens kilometres.
problem and its extent, only the radar detection of UAVs is
described in this paper shortly. Only for comparisons: the detection range of small-
dimensional targets (typically MoAA so called “RAM”
III. THEORETICAL BASIS category5) moving around 30 km for mortar shells, calibre 80 –
Analysing radars as the means for air-breathing threat 130 mm, and more than 50 km for unguided missiles, calibres
detection (esp. these LSS type) it is important to take into more than 100 mm.
consideration two factors on the one hand of a target and on the
other - the radar itself too. IV. EXPERIMENTS
For to verify the theoretical basis, the following
When using radar for LSS targets detection, the limiting experiments were performed:
factor is Radar Cross-Section (RCS) of the target. The radar
limitation lies in its carrier frequency f, or wavelength λ. The • RCS computation using simulation,
additional internal and external influences are questions of
particular radar technical solution, tactical employment within • RCS measurement in non-reflected chamber and
the terrain and combat formation, atmospheric condition,
proficiency of crews etc.
The simple view to the detectability of particular target is
that we have to select a proper λ, which corresponds to the
appropriate RCS. The radar usability of certain suitable 3
f ∈ <8 – 12> GHz, i.e. λ ∈ <3.8 – 2.5 cm>.
wavelength in view of the expected target range detection is 4
f ∈ <4 – 8> GHz, i.e. λ ∈ <7.5 – 3.8 cm>.
demonstrated in the Figure 1. 5
Rocket, Artillery, and Mortar targets.
• Tests of UAV detectability, explorinng the real sensor
from weaponry of the Air defencee troops of Czech
Army6.
It has been emerging, that for UVAs’ em mployment at short,
tactical radiuses (up to 10 km) or in the case of misusing UAV,
the copters will be more frequently employyed in comparison
with wing airplanes. For these reasons two tyypes of copters has
been chosen for experiments:
1. Qudrocopter Tarot FY650 and
2. Hexacopter DJI S8000.
Figure 3: Quadrocopter in SuperNEC simulation.
Simulative illumination wass done using several frequencies
(from 500 up to 4000 MHz, by step 0.5 GHz). The highest
frequency value, when SW SuuperNEC in the given computer
configuration was working corrrectly was 4350 MHz.
The average RCS values measuured at f = 4350 MHz were [m2]:
• Qudrocopter without loaad ..................0.21;
Figure 2: Hexacopter DJI S8000 • Qudrocopter + load ............................0.3;
Detailed technical specifications of these aircrafts
a are listed • Hexacopter without loadd ....................0.38;
in [1].
• Hexacopter + load..............................0.4.
The foundations for experiments werre for one thing
As the “load” the metal-coopper cube was used (soldered
verification calculation, simulations and form
mer experiments in
“Cuprextit” plates). Dimensionss: cube edge length d = 0.1 m.
the field of RCS measurement and for f another ones
groundwork acquired from factory and trooops trials. These B. Laboratory measurements
practical trials were done in competence of the domestic Experiments were realised in non-reflected chamber at the
producer and air defence troop’s authorities of
o the Czech Army Department of Radar Technollogy, UoD Brno. The chamber
General Staff. was for this reason re-configurred and calibrated at 10 GHz –
A. Simulations including applied instruments. The RCS measurements were
done with “empty objects” at first
fi and then with copters + load
Simulations were conducted using sim mulation software
– represented by the metal cubee defined above.
(SW) SuperNEC 7 at the Department of Radar
R Technology,
University of Defence (UoD) Brno. Principlees of measurement Both copters were placed on o the turntable, and when rotate
methods and the SW itself are defined sufficiently
s in the around by 360° measured stepw wise. For the measurements to be
software documentation. Some problems, inccluding SuperNEC more real – like radar detectionn in the terrain environment – the
SW description and application, were solveed in thesis at this hexacopter + load was canted about
a approx. 20 degrees.
department.
Measured values: average RCS/standard
R deviation/ extreme
Simulation had started by making modells, using graphical RCS when objects were turneed to the maximum reflexivity
interface („SIG GUI“) based on specimens - real objects direction [m2]:
(copters named above): physical dimensioons measurement,
structural material specification and constrructions modelling • Qudrocopter, empty .............. 0.08 / 0.02 / 0.25;
itself. The reflected energy was then measured.
m Results • Qudrocopter + load ............... 0.14 / 0.03 / 0.75;
demonstrate Figure 3.
• Hexacopter, empty ................ 0.22 / 0.04 / 0.5;
• Hexacopter + load ................ 0.33 / 0.05 / 1.2;
6
252. battalion/25. Air-Defence brigade, Strakonice. • Hexacopter, cant+ load .......... 0.23 / 0.07 / 0.44.
7
Producer: KEYSIGHT Corp., California, USA.
1.4
communication capabilities, reequirements the law concerning
civil aviation rules etc. Posts were
w recognised in advance using
1.2 both military plus ortho-photo maps, and they were examined
personally in real terrain too.
1
Copters took off at thee specified places and their
0.8 detectability by radar was checkked. The quantity was evaluated
RCS [m2]
as “SCAN” - for individual reflection
r and “TRACK” - for
0.6
continues coordinates measurem ment, including plot production.
0.4 During the experiment addiitional measurements were done
simultaneously - to fully utilize detached technique and crews:
0.2
• Copters’ detectability byy the naked eye;
0
0 50 100 150 200 250 30
00 350 400
uhel [deg]
angle • Copters’ detectability byy eye + binoculars;
• Detectability in the infraared spectrum;
Figure 4: Quadrocopter, empty
2.5
• Slant range measuremennt by laser rangefinder.
8
vrtul.
Hexa,6empty The military subsystem “ReTOB”
“ was used for these
2
vrtul.
Hexa +6 load
+ krychle measurements. The results aree not the part of this paper and
they will be published later.
1.5
The copters carried out thee take-off and they ascended to
the AGL (Above Ground Levvel) enabling the overspanning
RCS [m2]
hidden angles to radar directionn. After remaining at the spot for
1 a couple of tens seconds, they fly
f repeatedly to the basic station
(ReVISOR position, green poinnt No 1 in the Figure 6) and back
again - over the start-point position. This sequence was
0.5
repeated two times at minimum m. The extent of experiment was
limited namely by statutory reegulations 9 , which allow to fly
0 “within sight” and up to 300 m AGL.
0 50 100 150 200 250 30
00 350 400
uhel [deg]
angle
The copters’ take-offs weere done in reverse order than
described in paragraphs “S Simulations” and “Laboratory
Figure 5: Hexacopter empty and with load measurement” above. The reason was the following
The values measured during experimentss have come up to assumption: the configurationn “hexacopter + load” has the
expectation and estimation. It is possible to say, that they biggest RCS and the “Quadrocopter - empty“ the smallest one.
correspond with reality. For the next anallysis and possible Example: in the case the configuration „Quadrocopter + load“
experiments we can calculate with RCS meaasured within “X” detection was impossible, theen the experiment at the given
band between 0.2 and 0.3 m2 for hexacopreer, or between 0.1 position was ended.
and 0.2 m2 for qudrocopter. The additional looad increases RCS
approx. one third (using the concrete metal cube
c in the case of
this experiment, but it could be significantlyy different in other
cases in practise). The slant of target plays a big part: owing to
it, the RCS has been changing considerably.
C. Measurements in the field
Detectability in terrain was realised byy using the radar
sensor, introduced into Air-Force inventorry for to support
VSHORAD (Very Short Air-Defence) unitts of Czech Army
air-defence. This radar is presented under thee commercial name
“ReVISOR”. It is two-dimensional radar, working in “X” band,
pulse mode. The declared range to a standaard aircraft is more
than 30 km. The detailed description is lissted in the factory
documentation [4]. During the experiment the whole system
was operated by professional crews of air-deffence unit.
Airspace reconnaissance, concentrated onn the UAVs’ take-
off places, was done according to methodoloogy worked out by Figure 6: Configuration of exxperiment - terrain Strakonice
the author of this paper. The take-off plaaces were moving
away approx. by step 1 – 1.5 km. Their choicce respected terrain 8
Producer: RETIA s.c. Pardubice.
condition, hidden angles, frequenccy coexistence, 9
Act about civil aviation č. 49/1997 Sbb. and related regulations
Despite of the fact, that it is forbidden to publish exact
data 10 , it is possible to state, that targets of “mini-UAV”
category having RCS ∈ <0.1 ÷ 0.4 m2> were detected reliably
and at distances declared by producer.
D. Conclusions
The main contribution of this work to the military science is
a verifying the capability of radar means to detect small, slow
and low-flying targets. This capability was proved using
simulation, laboratory and terrain experiments as well.
Outputs of this work will be finalized and elaborated in the
near future for to be usable by military industry and Air-Force
command authorities of the Czech Army. There is an
assumption, the security organs generally - and especially
Ministry of the Interior - will be interested in this issue too.
ACKNOWLEDGMENT
The work presented in this paper has been supported by the
Ministry of Defence of the Czech Republic (Project PRO
K208).
REFERENCES
[1] DOJCAN, J. Technical specification QUADROCOPTER TAROT F650
and HEXACOPTER DJI S800E. JamCopters LTD, Brno 2014.
[2] KRATKY, M. Ground Based Air Defence Technologies for to Fight
Unmanned Aerial Vehicles. Habilitation thesis (delivered for defence).
University of Defence Brno, 2015.
[3] Pub-31-24-01. Použití pozemní protivzdušné obrany AČR v operacích.
Vojenská publikace. Praha 2007.
[4] RETIA I.C. Technický popis RVR a jeho začlenění do ASVŘP. Projekt
RD 041 005, ver. 1.03. Pardubice, 2014.
[5] USA Department of Defence. Unmanned Aerial Vehicles Roadmap
2002 - 2027. Office of the Secretary of Defence, Washington, D.C. USA
2002.
10
Figures concerning to established operational weaponry.
