Unit-3:

Antenna
Fundamentals
Prof. R.S.Bhadade
MIT, Pune
 Contents
• Unit-3 Syllabus
• Block Diagram of Communication System
• Introduction to Transmission Lines
• Introduction to Antenna (Ch.1)
• Types of Antenna (Ch.1)
• Radiation mechanism (Ch.1)
• Fundamental Parameters of Antenna (Ch.2)
• Radiation Integrals (Ch.3)
 Unit III : Antenna Fundamentals (6L)
• Introduction, Types of Antenna, Radiation
Mechanism. (Ch.1:- 1.1 to 1.3)
• Antenna Terminology: Radiation pattern,
radiation power density, radiation intensity,
directivity, gain, antenna efficiency, half power
beam width, bandwidth, antenna polarization,
input impedance, antenna radiation efficiency,
effective length, effective area, reciprocity.
(Chapter 2 :- 2.1 to 2.6 , 2.8 , 2.9 , 2.11 to 2.15 )
 Cont.
• Radiation Integrals: Vector potentials A, J, F,
M, Electric and magnetic fields electric and
magnetic current sources, solution of
inhomogeneous vector potential wave
equation, far field radiation.
(Chapter 3: 3.1 to 3.6)
Text Book:-
1. Antenna Theory-Design and Analysis
By C.A.Balanis (Chapter 1 to 3)
 Block Diagram of a Communication System

98.3MHz
• Most critical component.
• Last device at the transmitter.
• First device at the receiver.
• A good design of the antenna can relax system
requirements and improve overall system
performance.
• Eye of a communication system.
Introduction
to
Transmission
Lines
 Real Transmission Lines
1. 50Ω :- RF, Microwave (Lab.)
2. 75Ω :- DTH antenna to Set top box (STB)
Yagi-uda antenna to TV receiver
Cable TV
3. 300Ω :- Twin lead or flat (Yagi-uda antenna to TV
receiver)
4. 600Ω :-Telephone line-
Why 50 Ω ?
Impedance Matching
Power Transfer Efficiency
 Transmission Line Terminated With Z0

V refl =0 (Matched line)

No standing-wave pattern due to energy flowing in one direction

only.
Transmission Line Terminated with Short, Open

Vinc = V refl (open circuit)

Vinc = - V refl (short circuit)
S=Unity (Pure traveling wave)
S=Infinite (Pure standing wave)
 Open circuit termination

Important points:
+ve sign of Zin(d) => Inductive behavior
–ve sign of Zin(d) => Capacitive behavior
At λ/4 Zin(d)= 0
At λ/2 Zin(d)= ∞
After every λ/2 the entire periodic process is repeated.
 Short circuit Termination

Important points:
+ve sign of Zin(d) => Inductive behavior
–ve sign of Zin(d) => Capacitive behavior
At λ/4 Zin(d)= ∞
At λ/2 Zin(d)= 0
After every λ/2 the entire periodic process is repeated.
High-Frequency Device Characterization (VNA)
 Resonant Transmission Lines
(Resonant Antennas)

I/P Signal Standing waves Open Circuit

 Non-resonant Lines
(Non-resonant Antennas)

I/P Signal Traveling waves

Load Impedance
 Ch.1 Introduction to Antenna
• An antenna is defined as “a usually metallic
device (as a rod or wire) for radiating or
receiving radio waves.”
• The IEEE Standards:-the antenna or aerial as
“a means for radiating or receiving radio
waves.”
• Unguided structure.
• The antenna is the transitional structure between free-
space and a guiding device, as shown in Figure 1.1.
Guiding device or Transmission line
• The antenna impedance is represented by
ZA = (RL + Rr ) + j XA RA = ( RL + Rr )
RL = Load resistance (Loss resistance due to conduction
and dielectric losses in antenna structure).
Rr = Radiation resistance, is used to represent radiation
by the antenna. (Real part)
XA = Reactance of the antenna (imaginary part)
• Under ideal conditions, energy generated by
the source should be totally transferred to the
Rr .
• However, in a practical system there are
a) conduction-dielectric losses (in transmission
line and antenna)
b) reflections (mismatch) losses at the
interface between the line and the antenna.

Maximum power delivered to the antenna under conjugate

matching. ZA= (RA + jXA) ZG= (RG - jXG)
• The losses due to the line, antenna, and the
standing waves are undesirable.
• The line losses- selecting low-loss lines (tanϴ)
• The antenna losses- reducing the RL
• The standing waves can be reduced –
Impedance matching (ZA = Zo )
Types of
Antennas
 1) Wire Antennas
# Wire antennas , linear or
curved , are some of the oldest ,
simplest , cheapest.
# They are seen virtually
everywhere- on automobiles ,
buildings , ships ,aircraft .
# There are various shapes
( dipole , loop , and Helix)
#Loop antenna may take the
form of rectangle , square ,
ellipse.
# The circular loop is the most
common – simple in construction
4/27/2023 MIT,Pune 30
 2) Aperture Antennas
# These are very useful for
aircraft and spacecraft
applications , because they
can be conveniently flush-
mounted on the same.

#They can be covered with

a dielectric material to
protect them from
hazardous conditions of the
environment
4/27/2023 MIT,Pune 31
 3) Microstrip Antennas
# The metallic patch can take many different
configurations , however the rectangular
and circular patches are the most popular-
ease of analysis and fabrication ,

# These are low profile , conformable to

planar and nonplanar surfaces , simple and
inexpensive to fabricate using modern
printed-circuit technology , compatible
with MMIC designs , and very versatile in
terms of resonant frequency , polarization ,
pattern , and impedance.

# These can be mounted on the surface of

high-performance aircraft , spacecraft ,
satellites , mobiles , cars , and even
handheld mobile telephones.
4/27/2023 MIT,Pune 32
 4) Array Antennas
# These are used to produce the
desired radiation characteristics.
# Five controls that can be used to
shape the overall pattern of the
antenna:
1) The geometrical configuration of
the overall array ( linear ,
circular , rectangular )
2) The relative displacement
between the elements.
3) The excitation amplitude of the
individual elements.
4) The excitation phase of the
individual elements.
5) The relative pattern of the
individual elements.
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GMRT (Khodad, Narayangaon, Pune)
Ooty Radio Telescope
TV Broadcasting/Relay Antenna
Omnidirectional pattern
(360◦ coverage)
 5) Reflector Antennas
# Various geometrical configurations
( plane , curved reflectors ( especially
the paraboloid) ).

# Widely used in radio astronomy ,

microwave communication , satellite
tracking , and DTH.

# They are usually large in diameters

to achieve the high gain required to
transmit or receive signals over great
distances.

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Earth Station Satellite

VSAT DTH
 Radiation Mechanism
Side view Top view

Thickness Diameter
of DC Signal (f=o) of
conductor conductor

AC Signal (f1 , f2 ,
& f3 ) δ
f3>f2>f1
δ

δ << a
at HFs
4/27/2023 MIT,Pune 40
 Cont.
• Important Points:
• Skin depth or penetration depth decreases with
increase in frequency. (δ is 1/√∏fµσ)
• The E and H can hardly propagate through good
conductors.
• The fields and associated currents are confined to a
very thin layer (the skin) of the conductor surface.
• Hollow tubular conductors are used instead of solid
conductors in TV antennas.

4/27/2023 MIT,Pune 41
 Displacement current

Conduction current

Dielectric

(Displacement current)

Conduction current

Conduction current = Displacement current

 Transmission Line

AC Source,
with f

S >>λ

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• Radiation mechanism:-
1. If a charge is not moving, current
is not created and there is no
radiation.
2. If charge is moving with a uniform
velocity:
a. There is no radiation if the wire
is straight, and infinite in extent.
b. There is radiation if the wire is
curved, bent, discontinuous,
terminated, or truncated, as
shown in Figure 1.10.
3. If charge is oscillating in a time-
motion, it radiates even if the wire
is straight.
Sine, Triangular, Square wave , etc
 Half-Wavelength Dipole (λ/2)
1) Length , l= λ/2
λ= operating wavelength of
the signal.
f=c/ λ
2) It is a Resonant antenna
(Principle of resonance)
3) Zin=73+j42.5 Ohm (at l= λ/2)
4) Radiation resistance=73 Ohm
5) Impedance matching is done
by reducing its length till
inductive part vanishes. λ=C/fc = 3*108/98.3 (MHz)

λ/2= length of dipole

E and H plane of a λ/2 dipole
| λ/4 | λ/4 |

4/27/2023 MIT,Pune 48
 Folded Dipole (Extension of Dipole)
1) Folded Dipole (Broadband dipole)
Zo=300 Ω (4* Dipole impedance)
Radiation pattern- similar dipole antenna
Driven element in Yagi-Uda antenna
2) Yagi-Uda Antenna- Reception of TV signal
 TV Signal link DBS-TV
TV Rebroadcasting
Station- DD-I/II
(Sinhagad , Pune )

Down-link

DD Kendra, Worli, Mumbai

 Monopole or Quarterwave antenna
1) Length , l= λ/4
λ= operating wavelength of the
signal.
f=c/ λ
2) It is a Resonant antenna (Principle
of resonance)
3) Zin=36.5+j21.25 Ohm (at l= λ/4)
4) Radiation resistance=36 Ohm
5) Impedance matching is done by
reducing its length till inductive part
vanishes. λ=C/fc = 3*108/98.3 (MHz)
λ/4=length of monopole
Radiation pattern
 Cont.

E-Plane – Distance
covered by the
antenna

H-Plane – Area
covered by the
antenna

4/27/2023 MIT,Pune 53
 Wave front
• The front of a wave is sometimes referred to as
an equiphase surface.
• In physics, a wave front is
the locus of points having the same phase:
a line or curve in 2D, or
a surface for a wave propagating in 3D.
• Plane wave - Plane wave front
• Cylindrical wave - Cylindrical wave front.
• Spherical wave (Antenna) – Spherical wave front.
 3-dimensional EM wave

Subject preparation:- X-direction

University paper :- Y-direction
University result :- Z-direction
Single - frequency of EM wave exhibits a sinusoidal
variation of E and H field in space
3D (spherical wave) to 2D (plane wave)
 2.1 INTRODUCTION
• Fundamental parameters are used to describe
the performance of any antenna.
• Some of the parameters are interrelated and
not all of them need be specified for complete
description of the antenna performance.
• Examples:
a. Gain = ecd* Directivity
b. HPBW=1/Directivity
 Coordinate system for antenna analysis

r:- 0 to infinite
Θ:- 0 to π
Φ:- 0 to 2π

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Azimuth angle (Ф= 0 to 2π )

Elevation angle (ϴ= 0 to π )

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 2.2 RADIATION PATTERN.
• An antenna radiation pattern or antenna
pattern is defined as “a mathematical function
or a graphical representation of the radiation
properties of the antenna as a function of
space coordinates.
• In most cases, the radiation pattern is
determined in the far field region.
• Radiation properties include :radiation
intensity , field strength , directivity , and
polarization.

4/27/2023 MIT,Pune 65
 How to obtain Radiation pattern
Log-periodic
Antenna

Dipole Antenna

Transmitter Stepper Motor

3 Important Points: Receiver

1. Distance between two antenna (far-field),
R≥ 2D2/λ
2. Frequency of both the antenna must be same.
3. Polarization of both the antenna must be same.
 Normalized patterns

All three patterns gives the same HPBW.

• In practice, the 3-D pattern is measured and recorded
in a series of 2-D patterns.
• However, for most practical applications, a few plots
of the pattern (ϴ , Ф = constant) + plots of the
pattern (Ф, ϴ = constant ).
• Some antennas, depending on their geometry and also
observation distance, may have only one, two, or all
three components.
• In general, the magnitude of the total electric field
would be
 2.2.1 Radiation Pattern Lobes
• Various parts of a radiation pattern are referred to as lobes,
which may be sub- classified:
• Major or Main lobe (the radiation lobe containing the
direction of maximum radiation)
• Minor lobe (any lobe except a major lobe , undesirable)
• Side lobe ( a radiation lobe in any direction other than the
intended lobe ) - Side Lobe Level (SLL)
In most radar systems, low SLL is very important to minimize
false target indications.
• Back lobe (a radiation lobe whose axis makes an angle of
approximately 180◦ with respect to the beam of an antenna) -
Front to Back Ratio (FBR)
Symmetrical
3D Polar plot

Linear 2D
Cartesian
plot
Actual :- ϴ (0 to π)
Over Polar plot :- ϴ (0 to 2π) Ф (0 to 2π)
 2.2.2 Isotropic, Directional, and
Omnidirectional Patterns
 Isotropic:
• A hypothetical lossless antenna having equal radiation in all
directions.
• Radiated fields are independent of ϴ and Ф directions.
• Radiation pattern is circle.
• Although it is ideal and not physically realizable.
• It is often taken as a reference for expressing the directive properties
of actual antennas.
• Go = Do =1 (all directional radiator)
• HPBW is maximum as compared to actual antennas.
• dBi - For use with isotropic antennas.
• Example:- 2.5 dBi
• Note: They are used only as theoretical (mathematical) references.
• They do not exist in the real world.
Sun (best example of isotropic source)
Solid sphere 2-D pattern (Circle
(in 3-D) in both planes)

Vertical plane

Horizontal
plane
Equipotential Surface
 Directional
• Having the property of radiating or receiving EM waves
more effectively in some directions than in others.
• This term is usually applied to an antenna whose Dmax >
λ/2 dipole.
• Reference :- Half-wave dipole.
• G & D (actual antenna) > Go & Do (isotropic)
• HPBW (actual antenna) < HPBW (isotropic)
• Actual antennas are directional antennas.
• Radiation pattern is not circle.
• Radiated fields are the functions of ϴ and Ф directions.
 Dipole Antenna

Omnidirectional
Pattern
Directional Pattern

Directional in E-Plane

Non-directional in
H-Plane

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An omnidirectional pattern is a special type of a directional
pattern.
Quantity Near-field (Reactive) Far-field (Radiated)

Energy Stores energy. Propagates (radiates) energy.

Can transfer energy via
inductive or capacitive
coupling.

Longevity Disappears when source Propagates until absorbed.

is turned off.

Shape of Completely dependent on Field Spherical waves.

Field source circuit At very long distances- plane
waves.

Wave Depends on source circuit Depends solely on propagation

Impedance and medium medium (η = 120π = 377 Ω in
free space).
 Radian
 Used to measure a plane angle.
1 rad:- The plane angle with its vertex at the center of a circle
of radius r that is subtended by an arc whose length is r.
 Steradian
 Used to measure a solid angle.
1 sr:- The solid angle with its vertex at the center of a sphere of
radius r that is subtended by a spherical surface area equal to that
of a square with each side of length r.
A = 4πr2, there are 4π sr (4πr2/r2) in a closed sphere.
• EM waves are used to transport information from one point to
the other.
• A real part represents the average (real) power density.
• The imaginary part must represent the reactive (stored) power
density associated with the EM fields.
• In later chapters, it will be shown that the power density
associated with the EM fields of an antenna in its far-field
region is predominately real and will be referred to as
radiation density.
 Isotropic source

Poynting vector will not be a function of spherical angles.

 Radiation Intensity (U)

• In a given direction, it is defined as “ the power

radiated from an antenna per unit solid angle”
• U = Prad/ΩA
• It is a far field parameter.
Two methods to compute radiated power
Isotropic source
 U=A cos (ϴ)

We can also use Cartesian plot

 Beamwidth
• The angular separation between two identical points
on opposite side of the pattern maximum.
• E(θ)@half-power = 0.707(Field pattern, linear
scale) OR 0.5 (Power pattern , linear scale) OR -
3dB (Power pattern , dB scale)
• HPBW=17° (Global beam)
• HPBW= 1 ° or 2 ° ( Microwave Links)
• HPBW ↑→Side lobe level↓→Directivity↓
• However, in practice, the term beamwidth, with no
other identification, usually refers to HPBW.

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Methods to Determine HPBW & FNBW
• 2-D Polar Plot
• 2-D Cartesian Plot

4/27/2023 MIT,Pune 102

 Antenna resolution

Most design criteria is HPBW=FNBW/2

Multi-beam antenna
Direct Broadcast Satellite -TV
If the direction is not specified, it
implies the direction of maximum
radiation intensity (maximum
directivity) expressed as Dmax
Maximum Directivity
• For an isotropic source :- D = 1
a. U = Umax = U0
b. power is radiated equally well in all directions.
• For actual antenna :- Dmax > 1 (FOM)
• The range of directivity:- 0 ≤ D ≤ D0
Antenna with orthogonal polarization components
Exact expression to compute the directivity
 Approximate (simpler ) expression used to compute the
directivity. It can also be used for design purposes.

The equation (2-26) and (2-27) is used in case of one pattern that has only one
major lobe and any minor lobes, if present, should be of very low intensity.
Usually ec and ed are very difficult to compute, but they can be
determined experimentally. Even by measurements they cannot
be separated. ecd is used to relate the gain and directivity.
 Gain
• Another useful measure.
• G=ecd D
• It takes into account :- eo and directional
capabilities.
• Directivity is controlled only by the pattern.
Relative gain
Power input must be the
same for both antenna

Reference antenna: Dipole or Horn

When the direction is not stated, the power gain is usually
taken in the direction of maximum radiation.
 Two types of Gains

It takes into account the losses of the antenna element itself,

it does not take into account the reflection (mismatch) losses.
 If |ᴦ|=0 ( or Z0=Zin) , then Gabs= G

In practice, Gain means Maximum Gain

 Bandwidth

• It is the range of frequencies, on either side of a

center frequency (usually the resonance frequency for
a dipole), where the antenna characteristics (such as
Zin , pattern, HPBW, polarization, SLL, G, D, ecd) are
within an acceptable value of those at the center
frequency.
• For broadband antennas:
Bandwidth = fH / fL
• For narrowband antennas:
% Bandwidth = {( fH - fL )/fc } * 100
• Bandwidth:-

Po

0.707Po

0 fl fr (or fc) fh (f MHz)

fh – fl = Bandwidth

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 Number of FM stations
• Standard FM broadcasting frequency:- 88 to 108 MHz
• Center frequency :- (108+88)/2 = 98 MHz
• BW/station:-200 KHz
• No.of channels (or stations) :- RF Bandwidth (20 MHz)/BW
per station (200 KHz) =100
• FM Transmitter Antenna (Narrowband, 200 KHz)
• FM Receiver Antenna (Wideband, 20 MHz)

4/27/2023 MIT,Pune 136

 Polarization
• Polarization of Antenna and Wave both are same.
• When the direction is not stated, the polarization is
taken in the direction of maximum gain.
• It is the curve traced by the end point of the arrow
(vector) representing the instantaneous E - field.
• The field must be observed along the direction of
propagation.
• It can be defined either by E or H field, but not both.
• Defining Polarization with E-field, H-field can be
computed using Maxwell’s equations.
 Radio Broadcasting
(AM, FM)

TV Broadcasting
 Circular Polarization

a. Helical antenna
b. Microstrip Patch
c. Two Crossed Dipoles

Used in :-
a. Satellite Communication
b. GPS
c. RADAR
Elliptical Polarization

Shape of Helical antenna

Input Impedance
Ig = |Vg| / 2 (RL+Rr)
Respective Power delivered
formulas is covered in
Antenna equivalent areas.
 ANTENNA RADIATION EFFICIENCY
• The antenna efficiency (eo) that takes into account -
reflection, conduction, and dielectric losses.
• The conduction and dielectric losses of an antenna are
very difficult to compute and in most cases they are
measured.
• Even with measurements, they are difficult to
separate and they are usually lumped together to form
the ecd efficiency.
• The resistance RL is used to represent the conduction-
dielectric losses.
 Antenna Equivalent Areas

• An antenna in the receiving mode, whether it is in the

form of a wire, horn, aperture, array, dielectric rod,
etc., is used to capture (collect) EM waves and to
extract power from them.
 Cont.
• With each antenna, we can define a number of
equivalent areas which describe the power capturing
characteristics of the antenna when a wave impinges
on it.
• In general, the total capture area is
Capture Area = Effective Area + Scattering Area +
Loss Area
Receiving mode
Effective area

Ig = |Vg| / 2 (RL+Rr)
The aperture efficiency is not easily determined.
Reflector antennas:- 55 to 68% (single feeds)
Horn antennas:- 65 to 80%
 Friis Transmission Equation
• It is used to analyze and design of a communications systems.
• Also called link design equation.
• It relates the power received to the power transmitted between
two antennas separated by a distance R > 2D2/λ.
• Flux density from isotropic source (Gt =1)
F= Pt / (4πR2) (W/m2)
• Flux density from actual antenna.
F= Pt Gt / (4πR2) EIRP / (4πR2) (W/m2)
EIRP = Effective Isotopically Radiated Power
• Power received by antenna with effective area
Pr= Ae × F (Watts)
Pr= Ae Pt Gt / (4πR2)
• Fundamental relationship in antenna theory between G and Ae
is
G = 4π Ae / λ2
• Pr= Pt Gt Gr / (4πR/λ2)
The term (4πR/λ2) is known as path loss
 Ch.3 Radiation Integrals and
Auxiliary Potential Functions
• Analysis :- Sources to E & H fields
• Synthesis :- E & H fields to Sources
• Analysis procedure:- Sources to Auxiliary functions
(Vector potentials) to E & H fields.
• The most common vector potential functions are :
A (Magnetic Vector Potential)
F (Electric Vector Potential).
• E and H fields are physically measurable quantities.
• Vector potentials are strictly mathematical tools.
• Vector potentials often simplifies the solution even
though it may require determination of additional
functions.
 F=Electric Vector Potential
J=Electric Current Source A =Magnetic Vector Potential
M=Magnetic Current Source

One-step procedure:- J, M ʃ E, H
Two-step procedure:
J, M ʃ A,F d /dt E, H
• On-step procedure:- limits of integration (or
boundary of sources)

• Two-step procedure:-
• It requires both integration and differentiation.
• Path 1 requires only integration.
• The integrands are much simpler.
• The most difficult operation is the integration (limits
of integration or boundary of sources) to determine A
and F.
3.4 ELECTRIC AND MAGNETIC FIELDS FOR ELECTRIC (J)
AND MAGNETIC (M) CURRENT SOURCES
3.5 SOLUTION OF THE INHOMOGENEOUS
VECTOR POTENTIAL WAVE EQUATION
Cont.
3.6 FAR-FIELD RADIATION
 A. Half-Wavelength Dipole (λ/2)
1) Length, l= λ/2
λ= operating wavelength of the
signal.
f = c/ λ
2) It is a Resonant antenna
(Principle of resonance)
3) Zin =73+j42.5 Ohm (at l= λ/2)
4) Radiation resistance = 73 Ohm
5) Impedance matching is done by
reducing its length till inductive
λ=C/f = 3*108/98.3 (MHz)
part vanishes. c

λ/2= length of dipole

E and H plane of a λ/2 dipole
| λ/4 | λ/4 |
 B. Folded Dipole (Extension of Dipole)
1) Folded Dipole (Broadband dipole)
Zo= N2 × Dipole impedance = 4 × 73 = 288 Ω
Radiation pattern - similar dipole antenna
Driven element in Yagi-Uda antenna
2) Yagi-Uda Antenna - Reception of TV signal
 TV Signal link DBS-TV
TV Rebroadcasting
Station - DD-I/II
(Sinhagad , Pune )

Down-link

DD Kendra, Worli, Mumbai

 3. Monopole or Quarter wave antenna
1) Length , l = λ/4
λ= operating wavelength of the signal.
f =c/ λ
2) It is a resonant antenna (Principle of
resonance)
3) Zin = 36.5 + j 21.25 Ohm (at l= λ/4)
4) Radiation resistance =36 Ω)
Impedance matching is done by
reducing its length till inductive part
vanishes.
λ=C/fc = 3*108/98.3 (MHz)
λ/4=length of monopole
Radiation pattern