RADAR Antennas

1. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
RADAR
Antennas



 

t
R nEi 
PG 
3
max
4
 4 kT0BF(S / N)1 Lt Lr Lp
2 2

2. R
A
D
A
R
S
Y
S
T
E
M
S
Antenna:
• An antenna is
• an electromagnetic radiator,
• a sensor,
• a transducer and
• an impedance matching device
• For Radar Application, A directive antenna which concentrates the
energy into a narrow beam.
• Most popularly used antennas are: Parabolic ReflectorAntennas
• Planar Phased Arrays
• Electronically steered Phased array
antennas
• A typical antenna beamwidth for the detection or tracking of aircraft
might be about 1 or 2°.

3. R
A
D
A
R
S
Y
S
T
E
M
S
R • An antenna is defined by Webster’s Dictionary as “a usually metallic
A device (as a rod or wire) for radiating or receiving radio waves.”
D
A • The IEEE Standard Definitions [IEEE Std 145–1983]: Antenna (or
R aerial) “a means for radiating or receiving radio waves.”
S
Y
S
T
E
M
S
E & H Fields surrounding anAntenna Antenna as a transition device

4. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
Transmission-line Thevenin equivalent of antenna in transmitting mode
ZA  RA  jX A
 (Rr  RL ) jX A
Where ZA : antenna impedance
RA : Antenna resistance
Rr : radiationresistance
RL :loss resistance (i.e. due to conduction & dielectric losses)
XA : equivalent antenna reactance

5. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
ANTENNA PARAMETERS
• Circuit Parameters
• Input Impedance
• Radiation Resistance
• Antenna Noise Temperature
• Return Loss
• Impedance bandwidth
• Physical Quantities
• Size
• Weight
• Profile
• Shape
• Electromagnetic Parameters
• Field Pattern
Directivity, Gain)
(Beam Area,
• Radiated power
• Efficiency
• Effective Length and effective area
• Polarization (LP/CP/EP)

6. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
TYPES OF ANTENNA

7. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
TYPES OF ANTENNA
• Structural classification:
• WireAntennas
• ApertureAntennas
• MicrostripAntennas
• ArrayAntennas
• ReflectorAntennas
• Frequency dependency classification:
• Frequency DependentAntennas
• Frequency IndependentAntennas

8. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
Dipole antenna Circular (Square) loop antenna
Helix antenna
Wire Antennas

9. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
Horn antennas
Aperture Antennas
Conical Horn antennas
Slotted Waveguide antennas

10. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
Pyramidal Horn antennas
Radiation pattern of a antenna

11. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
Rectangular patch antennas
Microstrip Antennas
Circular patch antennas

12. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
Yagi-Uda antenna
Array Antennas
Microstrip array antenna
Slotted waveguide array antenna

13. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
Parabolic reflector antenna with front feed
Reflector Antennas
Parabolic reflector antenna with cassegrain feed
Corner reflector antenna

14. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S

15. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
Frequency independent antennas
Log periodic antenna Planar Log periodic slot antenna Log-spiral antenna
Discone antenna
Various versions of Biconical antennas – Infinite
Biconical antenna, Finite Biconical antenna, a cone
with finite ground, a cone with a stem and discone

16. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
FUNDAMENTAL PARAMETERS OF ANTENNA
• Radiation pattern
• Radiation power density
• Radiation intensity
• Beamwidth
• Directivity
• Antenna efficiency
• Gain
• Bandwidth
• Group Delay
• Polarization
• Antenna impedance
• Antenna temperature
• Brightness Temperature
• Antenna Factor

17. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
Radiation pattern
A graphical or mathematical representation of the radiation properties of
an antenna such as amplitude, phase, polarization etc as a function of
the angular space coordinates θ and Φ.
Polar pattern Linear pattern

18. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
Directional radiation pattern Omni-directional radiation pattern
Radiation pattern

19. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S • Same power is radiated
• Radiation intensity is power density over sphere (watt/steradian)
• Gain is radiation intensity over that of an isotropic source

20. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
Field regions of an antenna
(a) Reactive near field region
(b) Radiating near field (Fresnel) region
(c) Far field (Fraunhofer) region
Field regions of an antenna

21. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
[0.62 D3
/   R  2D2
]

22. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
Radiation power density
Where W = Radiation power density (W/ m2)
E = radiated electric field intensity (V/ m)
H = radiated magnetic field intensity (A/ m)
*
2
1
av E  H 
W x, y, z Re
The time average Poynting vector (average power density) can be
written as

23. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
It can be defined as “the ratio of the radiation intensity in a given direction
from the antenna to the radiation intensity averaged over all directions”
Directivity (D)/ Directive Gain

4U
Prad
D(dB) 10log10[D(dimensionless)]
Where, D = directivity (dimensionless)
U = radiation intensity (W/ unit solid angle)
U0= radiation intensity of isotropic source (W/ unit solid angle)
Prad= total radiated power (W)
D 
U

U
U0 Prad /4

24. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
A 1r 2r
0
D 
4 
4
  
Where, D = directivity (dimensionless)
ΩA = beam solid angle)
θ1r= HPBW in one plane (radian)
θ2r= HPBW in a plane at a right angle to other (radian)
If beamwidth in degrees, equation can be written as:

2
1d2d 1d2d
1r 2r
4180
0
180
180


1d ( )2d ( )
D 
4 
4
 
 
41253
For a planar arrays, a better approximation is
D 
32400
1d 2d
0
 

25. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
Radiation pattern for a particular paraboloid reflector antenna

26. R
A
D
A
R
S
Y
S
T
E
M
S
S
Y
S
T
E
M
S
Antenna efficiency
R
A
D
A
R
e0  ereced
 erecd
Where, e0 = total antenna efficiency(dimensionless)
ecd = antenna radiation efficiency(dimensionless)
: used to relate the gain and directivity
er = reflection (mismatch) efficiency (dimensionless)
ec = conduction efficiency(dimensionless)
ed = dielectric efficiency(dimensionless)
2
0 cd
 e  (1  )e

27. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
ZL ZC
 ZC
 
ZL
Where, ZL= Antenna impedance
ZC = characteristic impedance

28. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
Gain (G)/ Power Gain
RelativeGain 
4U, (dimensionless)
Pin(isotropicsource)
Where, D = directivity (dimensionless)
U = radiation intensity (W/ unit solid angle)
Pin= total input power (W)
Prad= total radiated power (W)
ecd= antenna radiation efficiency (dimensionless)
total input(accepted )power
radiation intensity
P
Gain 
in

4U,(dimensionless)
Prad  ecd Pin
D(dimensionless)
P
P P /e
 Gain
rad
cd cd
in rad cd
 e

4U, e
4U, 4U,

29. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
The relationship between the gain and the beamwidth of an antenna
depends on the distribution of current across the aperture.
For a "typical" reflector antenna the following expression is sometimes
used:
1d2d
Where, θ1d = HPBW in one plane (degree)
θ2d= HPBW in a plane at a right angle to other (degree)
G 
20000

30. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
Effective Aperture (Aeff)
4Aeff
2
G  2

4 A
e

Where, = wavelength
A= Physical area of the antenna
e = antenna apertureefficiency

31. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
• Antenna can be modeled as an impedance
• Ratio of voltage to current at feed port
• Design antenna to maximize power transfer from transmission line
• Reflection of incident power sets up standing wave
• Input impedance usually defines antenna bandwidth
Antenna Input Impedance

32. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
Bandwidth
fH  fL
ABW  f H  fL
 fL
FBW  2
fH
Bandwidth of the antenna is defined as the range of frequencies within
which the performance of the antenna provides desired characteristics.
•Generally, Impedance BW when S11  -10dB [VSWR  2]
The frequency bandwidth of an antenna can be expressed
Absolute Bandwidth (ABW)
Fractional Bandwidth (FBW).
(2.1)
Where, fH and fL denote the upper edge and the lower edge of the antenna
bandwidth, respectively.
For broadband antennas, the bandwidth can also be expressed as the
ratio of the upper to the lower frequencies, where the antenna performance
is acceptable

33. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S

34. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S

35. R
A
D
A
R
S
Y
S
T
E
M
S
S
Y
S
T
E
M
S
Polarization (2.1)
R Polarization is defined as “the electric field vector of an antenna oriented
A in space as a function of time”.
D
A
R
Electromagnetic Wave

36. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
(2.1)
The polarization of a radiated wave is the property of an electromagnetic
wave describing the time varying direction and relative magnitude of the
electric-field vector at a fixed location in space, and the sense in which it
is traced, as observed along the direction of propagation.
There are three classifications of antenna polarization:
• Linear polarization,
• circular polarization and
• Elliptical polarization.
#Circular and linear polarizations are special cases of elliptical polarization

37. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
(a) Rotation of plane electromagnetic wave and
(b)its polarization ellipse at z =0 as a function
of time

38. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
Polarisation states for a z-directed plane wave

39. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
Note : Both the PLF and p lead to the sameanswers
Polarization Loss Factor

40. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
• The antenna factor is defined as the ratio of the electric field strength
to the voltage V (units: V or µV) induced across the terminals of a
antenna.
• For an electric field antenna, the field strength is in units of V/m or
µV/m and the resulting antenna factor AF is in units of1/m:
AF= Eincident/Vreceived
Antenna Factor
• In a 50 Ω system, the antenna factor is related to the antenna gain G and the
wavelength λ via: AF= [9.73/ (λ*G1/2)]

41. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S

42. R
A
D
A
R
S
Y
S
T
E
M
S
R
A
D
A
R
S
Y
S
T
E
M
S
• Most popularly used antennas are:
• Parabolic Reflector Antennas
• Planar Phased Arrays
• Electronically steered Phased array antennas
RADAR ANTENNAS

43. R
A
D
A
R
S
Y
S
T
E
M
S
Radar Antenna ArchitectureComparison

44. R
A
D
A
R
S
Y
S
T
E
M
S
Array Radar
Passive Array Radar Active Array Radar

45. R
A
D
A
R
S
Y
S
T
E
M
S
Active Phased Array Radar

46. Digital Array Radar Architecture:
Digital on Receiver
R
A
D
A
R
S
Y
S
T
E
M
S
Each active analog T/R module is followed by an A/D for immediate digitization
Multiple received beams are formed digitally by the digital beam-former.

47. R
A
D
A
R
S
Y
S
T
E
M
S
Reference
1. C A Balanis, Antenna Theory and Design, 3rd Edition, Wiley, 2005.
2. G Kumar and K P Ray, Broadband Microstrip Antenna, Arctech
Publication, 2003.
3. R K Shevgaonkar, Electromagnetic Waves, 2006