Introduction to Radar, Radar classification, The simple form of the Radar equation, Radar block diagram and operation, The Doppler Effect, Simple CW Radar Block Diagram, Block diagram of CW doppler radar with nonzero IF receiver, Applications of CW radar, Block Diagram of Frequency Modulated CW Radar radar range equation

1. Dr. P.Surendrakumar
Associate Professor
ECE Department
Bapatla Engineering College, Bapatla
Radar Engineering
Unit-1

2. UNIT-III
Introduction to Radar, The simple form of the Radar equation, Radar
block diagram and operation, The Doppler Effect, Simple CW Radar
Block Diagram, Block diagram of CW doppler radar with nonzero IF
receiver, Applications of CW radar, Block Diagram of Frequency
Modulated CW Radar.
Radar Systems

3. Introduction
• RADAR- Radio Detection and Ranging
• Theory of reflection, absorption and scattering
• Higher the frequency better the result
• Location parameters: Range, height, direction, direction of motion,
relative velocity

8. Swathi Radar By DRDO
• The Defence Research and Development Organisation (DRDO) developed six more
locating radars Swathi weapons. Meanwhile, these powerful weapons will be
procured by the Indian Army soon. This is a powerful weapon that can easily
distinguish between friends and foes. It's 400 crore project taken up by the Ministry
of Defence and it will enhance the capabiity of the Indian Army.

10. • Maritime, Aviation and Land navigational aids
• Height measurement (radar altimeter)
• Instrument landing (in poor visibility)
• Space applications (planetary observations)
• Radars for determining speed of moving targets (Police radars Law
enforcement and Highway safety)
• Remote sensing (weather monitoring)
• Air traffic control (ATC) and aircraft safety
• Vessel traffic safety
Applications

11. Military
• Detection and ranging of targets in all weathers
• Weapon control – aiming guns at target
• Early warning on approaching aircrafts or ships
• Direct guided missiles
• Search submarines, land masses and buoys
Applications

12. • Target distance is calculated from the total time (tdelay) taken by the
pulse to travel to the target and back
• c = 3 x 108 m/s, speed of light
Radar Ranging

13. Simple Radar Block Diagram

14. Detailed Radar Block Diagram

16. PPI Display of the Radar

19. A Monostatic Radar
Scan Pattern
Generator
Antenna Duplexer
Waveform
Generator
Transmitter
Receiver
Signal
Processor
Data
Extractor
Data
Processor
Radar
Display
Radar Block Diagram
TX RX
Radar Display

20. • Antenna is highly directive with large gain
• Duplexer switches automatically
• Tx remains silent during Rx period
• Tx pulse is high power, short duration
• Rx has sensitivity to receive weak echo signals and is be highly immune
to noise
Radar Block Diagram

21. Band Designation ITU Nominal
Frequency Range
Specific radar bands based
on ITU assignment
HF 3 – 30 MHz
VHF 30 – 300 MHz 138-144, 216-225 MHz
UHF 300 – 1000 MHz 420-450, 590-942 MHz
L 1 – 2 GHz 1215-1400 MHz
S 2 – 4 GHz 2300-2500, 2700-3700MHz
C 4 – 8 GHz 5250-5925 MHz
X 8 – 12 GHz 8500-10680 MHz
Ku 1 2– 18 GHz 13.4-14, 15.7-17.7 GHz
K 18 – 27 GHz 24.05-24.25 GHz
Ka 27 – 40 GHz 33.4-36 GHz
Radar Frequency Band
Designations

22. • Tx transmits a train of narrow rectangular shaped pulses
modulating a sine wave carrier
• The range to the target is determined by measuring the time taken
by the pulse to travel to the target and return to the radar
Pulsed Radar

23. Average Power
• In each cycle (Pulse Repetition Time), the radar only radiates
from t sec
• The average transmitted power is
where Pt = peak transmitted power and
PRF = Pulse Repetition Frequency,
. .
av t t
P P P PRF
PRT
t
t
 
 
 
 
1
PRF
PRT


24. Range Ambiguity
• The range that corresponds to the 2-way time delay is the
radar unambiguous range, Ru
• Consider detection of 2 targets,
Transmitted
Pulses
Received
Pulses
Pulse 1 Pulse 2
echo 1 echo 2
PRT
t
tdelay
tdelay
Ru
(R )
1
R2

25. Range Ambiguity
• Echo 1 is the return from target at range R1,
• Echo 2 is the return from the same target at range R1, from the 2nd
transmission
• Echo 2 can also be taken as an echo from a different target from the 1st
transmission
1
2
delay
ct
R 
2 1
2
delay
ct
R R
 
 
2
2
delay
c PRT t
R


ERROR!

26. Range Ambiguity
• The maximum unambiguous range is
,max
2 2
u
cPRT c
R
PRF
 

28. Range Resolution
• Range resolution, R, is the radar ability to detect targets in
close proximity as 2 distinct targets
• 2 close proximity targets must be separated by at least R to
be completely resolved in range
• Consider 2 targets located at ranges R1 and R2, corresponding
to time delays t1 and t2 respectively, the difference between
the 2 ranges is
 
2 1 2 1
2 2
c c
R R R t t t

     

29. Range Resolution
• To distinguish the 2 targets, they must be separated by at least
1 pulse width t,
where B = radar bandwidth 2 2
c c
R
B
t
  
Received
Pulses
return
target 1
c
return
target 2
t ct
target 1 target 2
ct

R R
1 2

30. • The number of wavelengths contained in the two way path
between the radar and the target,
• Total phase shift,
• Radar is able to give radial velocity
of a moving target from Doppler
Effect
• Doppler effect causes a shift in
frequency of the received echo
signal from a moving target
• Doppler frequency shift
• Let R be the Range of the target
Doppler Effect
RADAR TOWER
INBOUND
ECHO
RADAR
ANTENNA
TRANSMIT
PULSE
OUTBOUND
ECHO
2R
n


4
2
R
n

 

 

31. • When the target is moving, R and φ change
continuously
• The rate of change of φ is angular frequency
where vr = radial velocity of the target towards the
radar
• The Doppler frequency shift,
where
Doppler Effect
4
4
2 r
d d
v
d dR
f
dt dt

 
 
 
   
2
2 r o
r
d
v f
v
f
c

 
cos
r
v v 


33. Pulse Repetitive Frequency
• For a single pulse, the maximum unambiguous range, Ru,max, is
determined by the PRF,
• High PRF is unambiguous in Doppler but highly ambiguous in Range
since it meets the Nyquist sampling criteria for Doppler shift of all
targets design to detect but there is little time between pulses for
ranging
,max
2 u
c
PRF
R


34. Pulse Repetitive Frequency
• Medium PRF radar may be ambiguous in both Doppler and range since
it samples too fast for echoes from long range but too slow to Nyquist
sample the Doppler shift of all targets
• Medium PRF however has the best of both worlds, a compromise
performance between unambiguity in Doppler and range
• Low PRF is unambiguous in range but high ambiguous in Doppler since
it waits until the last transmitted pulse arrives before the next
transmission

35. Pulse Repetitive Frequency
• Different PRF is used in different application such as Low PRF or
Medium PRF is suitable for detection of vessels while High PRF is used
in detecting air targets
• Careful selection of PRF will also result in better tracking performance
since one must be able to detect a target before tracking it

36. Clutter
• Clutter is a term used for unwanted echoes in electronic
systems, particularly in reference to radars. Such echoes are
typically returned from ground, sea, rain, animals/insects,
chaff and atmospheric turbulences, and can cause serious
performance issues with radar systems.

37. Clutter

38. Simple CW Radar

40. Simple CW Radar with Zero IF

42. Isolation between Tx and Rx
• Via separation in frequency
• However not possible to eliminate the leakage completely
• A moderate signal is required to use it as a reference signal
• If this leakage is not available , a separate ref signal has to be
provided !!!!!
• Amount of transmitter leakage should be controlled
• Two factors: Max amount of power the receiver can withstand
and Amount of transmitter noise, hum, microphonics, stray
pickup and instability which enters the receiver from the txer.
• Additional noise by Txer reduces the receiver sensitivity
• Additional Isolation is required unless a good receiver and low
transmitter power is used.

43. Isolation between Tx and Rx
• Txer power vs receiver sensitivity
• 10mW is the safe power that can be applied to a Rxer, Txer power
is 1kW then the isolation required is at least 50 dB.
• Some times it is dictated by noise in long range radars
• Clutter can also contain noise
• In pulse radars it is protected by duplexer
• Turning off is possible in pulse radars
• In CW radar, the operation is continuous….
• Hybrid junction, rat race, circulator, Turnstile Junction or
separate polarizations, Separate antennas
• In hybrid junctions 20 to 30 dB isolation is obtained but waste
of power(6 dB loss).

44. Isolation
• No 6 dB loss in ferrite junctions and 20 to 50 dB isolation is
easily obtained
• Turnstile junctions have 40 to 60 dB isolation
For VSAT modems the transmission and reception
paths are at 90° to each other, or in other words, the
signals are orthogonally polarized with respect to each
other. This orthogonal shift between the two signal
paths provides approximately an isolation of 40 dB in
the Ku band and Ka band radio frequency bands.
Hence this device serves in an essential role as the
junction element of the outdoor unit (ODU) of a VSAT
modem. It protects the receiver front-end element (the
low-noise block converter, LNB) from burn-out by the
power of the output signal generated by the block up
converter (BUC). The BUC is also connected to the
feed horn through a wave guide port of the OMT
junction device.

46. CW Radar with Non-zero IF

48. CW radar with non zero IF
• Improvement in receiver sensitivity 30 dB compared to a homodyne
receiver
• Receiver BW: wide enough to pass the expected range of doppler
frequencies.
• In most cases of practical interest the expected range of doppler
frequencies will be much wider than the frequency spectrum
occupied by the signal energy. Consequently, the use of a
wideband amplifier covering the expected doppler range will result
in an increase in noise and a lowering of the receiver sensitivity.
• If the frequency of the doppler-shifted echo signal were known
beforehand, a narrowband filter-one just wide enough to reduce the
excess noise without eliminating a significant amount of signal
energy-might be used.
• If the waveform of the echo signal were known, as well as its carrier
frequency, the matched filter could be specified

49. Factors Spreading the CW
signal energy over a Band
• .
• Spectrum broadening is due to usage of finite duration CW, Cross
section variations, target accelerations, scanning fluctuations,