Working Processes Of Radar History – Before Radar Principle Of Operation Radio Detection And Ranging Radar Functions Radar Bands And Usage Terminology Of Radar Systems Radar Range Equation Types Of Radar Pulse RADAR Duplexer Using Pin Switches Doppler Effect Principle Of Continuous Wave Radar Principles Of MTI RADAR Different Types Of RADAR & It’s Applications

1. Microwave Communications
and Television
Nenavath Ravi Kumar
Associate Professor
ECE Dept-MIST

2. Principles of RADAR
Systems

3. Contents
• Working Processes Of Radar
• History – BeforeRadar
• PrincipleOfOperation
• Radio Detection And Ranging
• Radar Functions
• Radar Bands And Usage
• Terminology Of Radar Systems
• Radar Range Equation
• Types Of Radar
• Pulse RADAR
• Duplexer Using Pin Switches
• Doppler Effect
• Principle Of Continuous Wave Radar
• Principles Of MTI RADAR
• Different Types Of RADAR & It’s Applications

4.  They send sound waves that reflect
of an object just as electric
RADAR systems do.
RADAR is an acronym for RAdio
Detecting And Ranging.
First successfully demonstrated in
1936.
It uses electromagnetic waves.
It enjoys wide range of application.
WORKING PROCESSES OF RADAR

5. History – Before Radar
■ Between the World Wars,
parabolic sound mirrors, were
used to provide early
warming;
■ Acoustic mirrors had a limited
effectiveness, and the
increasing speed of aircraft in
the 1930s meant that they
would already be too close to
deal with by the time they had
been detected.
■ Radio transmitters had already
been in use for over a decade
for communications.
WW1
WW2
Top: (L) Bombing during the WW1, (R)
“Whisper Dishes” Bottom: (L) WW2
Bombers, (R) Four-horn acoustic
locator,1930s

6. The history of RADAR starts with experiments by Heinrich &
Hertz in the late 19th century.
The first form of RADAR created by humans was the
telemobilescope.
Telemobilescope ( The first form of RADAR )
 It was mainly used to detect ships to avoid collisions
HISTROY

7. History – Radio Detection
■ Radar was first patented and
demonstrated in 1904 by the German
engineer Christian Hülsmeyer;
■ Watson Watt is generally credited with
initiating what would later be called radar;
■ In June 17, 1935, a radio-based detection
and ranging was first demonstrated in
Great Britain;
■ The first Radar system used by the
British
comprised 21 stations placed along the
country’s eastern coast.
Left: (T) Christian Hülsmeyer, (B) Watson
Watt, Right: Chain Home coverage map

8. Principle of Operation
• The basic RADAR system consist of Transmitter, Duplexer,
Antenna, Receiver and Display shown in below figure.

9. Transmitter: It generates high power signals at microwave
frequency range, radiated into space by using an Antenna through
Duplexer towards the target for detection.
Duplexer: It is a switch which connects the transmitter or receiver
to the Antenna alternately.
Antenna: The same Antenna can be used for transmitter &
Receiver, It is a transiver Antenna. Used for transmitting
electromagnetic waves towards target & receive echo signal from
target.
Receiver: The reflected signals (echo signals) collected by the
transiver antenna.
Display: It is designed to present the received information.
RADAR Display: A-Scope, B-Scope, Plan-Position Indicator (PPI)
etc.

10. Principle of Operation
 Reflection of electromagnetic waves
 Measurement of running time of transmitted pulses

11. • Bistatic: the transmit and receive antennas are at different
locations as viewed from the target (e.g., ground transmitter and
airborne receiver).
• Monostatic: the transmitter and receiver are colocated as viewed
from the target (i.e., the same antenna is used to transmit and
receive).
• Quasi-monostatic: the transmit and receive antennas are slightly
separated but still appear to be at the same location as viewed from
the target (e.g., separate transmit and receive antennas on same
aircraft).
Radio Detection and Ranging
TARGET
TRANSMITTER (TX)
RECEIVER (RX)
INCIDENT WAVE
FRONTS
SCATTERED WAVE
FRONTS
Rt
Rr


12. Radar Functions
• Normal radar functions:
1.range (from pulse delay)
2.velocity (from Doppler frequency shift)
3.angular direction (from antenna pointing)
• Signature analysis and inverse scattering:
4.target size (from magnitude of return)
5.target shape and components (return as a function
of direction)
6.moving parts (modulation of the return)
7.material composition
• The complexity (cost & size) of the radar
increases with the extent of the functions that the
radar performs.

13. WHY MICROWAVE ???
Very compact
High Gain
Highly directional
Antennas
Radio frequencies
Suitable for most
applications

14. 6
Radar Bands and Usage
8

15. Fields of Applications
• Military Applications, Security,
Surveillances etc.
• Weather Observations.
• Air Traffic Control.
• RADAR Speed meter.
• Collision Avoidance RADARs.
• Inspection of Construction work.
• Road maintenances

16. Terminology of Radar Systems
• RANGE: The distance between Radar and target is called Range of
the target or simply range, R. We know that Radar transmits a signal to
the target and accordingly the target sends an echo signal to the Radar
with the speed of light, C.
Distance=Speed×Time
The two way distance between the Radar and target will be 2R
2R=C×T
R=C*T/2
• ECHO SIGNALS: The reflected electromagnetic signal from the
target is called “ECHO”.
• PULSE WIDTH (PW): it is the duration of the RADAR pulse. It
express in milliseconds.
• REST TIME (RT): It is the time interval between two pulses.

17. PULSE REPETITION TIME(PRT): It is the time interval between the
beginning of one pulse and beginning of next pulse.
It is the sum of Pulse Width (PW) and Rest Time (RT).
PRT = PW + RT
PULSE REPETITION FREQUENCY (PRF): The number of pulses transmitted
per second is called as PULSE REPETITION FREQUENCY .
It is the reciprocal of the pulse repetition time.
DUTY CYCLE (DC): It is the ratio of the Pulse width (PW) to the Pulse
Repetition Time (PRT).
Or
It is also defined as the product of Pulse Width and Pulse Repetition Frequency.

18. MAXIMUM UNAMBIGUOUS RANGE: The range beyond which targets
appear as second time around echoes is called as “Maximum Unambiguous
Range”.
Hence maximum unambiguous range is given by
RADOME: Radome is a sheltering structure for antenna which must be operated
in severe weather conditions (High winds, icing and extreme temperatures).
AZIMUTH & ELEVATION ANGLES OF THE TARGET:
Azimuth (Horizontal) Angle : It is antenna beam angle on the local horizontal
plane from same reference.
Elevation (Vertical) Angle: It is angle between RADAR antenna beam axis and
local horizontal.

19. Radar Range Equation
Pt
Power density from
uniformly radiating antenna
transmitting spherical wave
Pt = peak transmitter
power
R = distance from radar4  R2
R

20. Radar Range Equation (continued)
Power density from
isotropic antenna
Pt = peak transmitter
power
R = distance from radar
Pt
4  R2
Power density from
directive antenna
Pt Gt
Gt = transmitgain
4  R2
.
Gain is the radiation intensity of the
antenna in a given direction over
that of an isotropic (uniformly
radiating) source
Gain = 4  A / 2

21. Definition of Radar Cross Section (RCS or 
Radar Cross Section (RCS or ) is a measure of the
energy that a radar target intercepts and scatters back
toward the radar
Power of reflected
signal at target
t tP G 
4  R2
 = radar cross section
units (meters)2
Power density of reflected
signal at the radar
Pt Gt 
4  R2 4  R2
Power density of
reflected signal falls off
as (1/R2 )
Target
Radar
Antenna
Reflected Energy
R
Incident Energy
MIT Lincoln Laboratory
361564_P_21Y.ppt ODonnell
06-13-02

22. Radar Range Equation (continued)
Power density of reflected
signal at radar
Pt Gt 
4  R2 4  R2
Power of reflected signal
from target and received
by radar
Pt Gt
4  R2 4  R2
 Ae Pr = power received Ae =
effective area of
receiving antenna
rP =
The received power = the power density at the radar times the area of
the receiving antenna
Target
Radar
Antenna Reflected Energy
R

23. Sources of Noise Received by Radar
•The total effect of these noise
sources is represented by a
single noise source at the
antenna output terminal.
•The noise power at the
receiver is given by:
N = k Bn Ts
k = Boltzmans constant
= 1.38 x 10-23 joules / deg oK Ts=
System Noise Temperature
Bn = Noise bandwidth of receiverNoise from Many Sources Competes with
the Target Echo
Transmitter
Receiver
Solar Noise
Galactic Noise
Man Made
Interference
Atmospheric
Noise
( Radars, Radio Stations, etc)
(Receiver, waveguide, and duplexer noise)
Ground Noise
Courtesy of Lockheed Martin.
Used with permission.

24. Radar Range Equation (continued)
Signal Power reflected
from target and received
by radar
Average Noise Power N= k Ts Bn
Signal to Noise Ratio S / N = Pr / N Assumptions :
Gt = Gr
L = Total System Losses To =
290o K
Pt Gt  Ae
4  R2 4  R2
rP =
Signal to Noise Ratio (S/N or SNR) is the standard measure of a radar’s ability
to detect a given target at a given range from the radar
“ S/N = 13 dB on a 1 m2 target at a range of 1000 km”
radar cross section of target
s n
Pt G2 2 
(4  3 R4k T B L
S / N=

25. Types Of Radar

26. Primary Radar
A Primary Radar transmits high-frequency signals
which are reflected at targets. The arisen echoes
are received and evaluated.
Secondary Radar
At these radar sets the target must have a
transponder (transmitting responder) on board
and this transponder responds to interrogation by
transmitting a coded reply signal.

27. Pulse RADAR
Block Diagram

28. Trigger Source: It provides pulses for the modulator. It is
also called synchronizer.
Pulse Modulator: It provides rectangular pulses which
acts as the supply voltage to the output tube.
Output Tube: It can be magnetron or reflux klystron or
TWT as per requirement. If an amplifier is used, a source
of microwave is also required.
Antenna: Usually Parabolic reflector antenna is used for
both transmission and reception.
Duplexer: It consists of two gas discharge tubes of fast
RF switches namely Anti Transmit Receiver (ATR) tube
and Transmit – Receiver (TR) tube.
Low Noise RF Amplifier: It is the first stage of the
receiver. It amplifies the received signal to desired level.
This is done by a TWT amplifier or parametric amplifier.

29. Mixer & Local Oscillator: These convert RF signal
output from RF amplifier to low frequency levels called
Intermediate Frequency. Thus in a mixer stage, the carrier
frequency is reduced.
IF Amplifier: It consists of cascade of tuned amplifiers
and provides high gain. IF range is 30MHz or 60MHz.
Detector: It demodulates the signals coming from the IF
amplifier and its output is given to the video amplifier.
Generally schottky diode is used for demodulating
received echo signals.
Video Amplifier: The output of the detector is amplified
by video amplifier to the specified level
Display: It provides visual information.

30. Advantages & Disadvantages of
Pulse RADAR
Advantages:
• It is simple in design & Operation.
• No need for accurate synchronization.
• Range can be increased by increasing. transmitted
power or by increasing diameter of parabolic reflector
of antenna.
Disadvantages:
• It cannot measure the velocity of moving target but
only can measure range.
• Clutters can cause several problems.
• Moving Target cannot be detected.

31. DUPLEXER USING PIN SWITCHES:
DUPLEXER USING CIRCULATOR:

32. DUPLEXER operation
• A branch type duplexer consists of two fast RF
switches are called
• Transmit – Receive (TR) Switch or TR Tube.
• Anti- Transmit – Receiver (ATR) Switch or ATR
Tube.
• The TR tube consists of resonant cavity associated
with the cathode tube. Tube itself contains an inert
gas (Helium or Neon) at low pressure.
• When gas tube is in operation, resonant cavity
permits energy to be transferred freely from input to
output line.
• An ATR tube is a TR tube with no output.

33. DOPPLER EFFECT
• The frequency shift in the received echo signal
in the RADAR due to the moving target is
known as “DOPPLER EFFECT”.
• The Doppler frequency shift (fd) is given by
• Where – Doppler shift frequency.
VR – Relative Velocity
λ – wavelength of the transmitted wave

34. Principle of Continuous Wave Radar

35. Principle of CW RADAR
• It uses the Doppler effect to detect frequency change caused by
a moving target and displays this as a relative velocity.
• The transmitted energy being continuous duplexer is replaced
by a circulator. Circulator provides isolation between the
transmitter and the receiver.
• The transmitted frequency ft is received as the target moves
from the RADAR.
• These incoming echo signals (ft±fd) are heterodyned with
locally generated transmitted signal (ft) inside a mixer.
• The output of the detector is applied to the Doppler amplifier. Is
to eliminate the echoes from the stationary targets and to
amplify the Doppler echo signals (fd).
• The indicator displays the velocity of the target.

36. Advantages & Disadvantages of CW
RADAR
Advantages:
• Accurate measurement of relative velocity of the target.
• Simple Circuit
• Low power consumption
• Small in size
• It is used at low transmitting power.
Disadvantages:
• It doesn’t give information about range.
• If large number of targets, it does not give accurate
results.

37. Principles of MTI RADAR
• MTI stands Moving Target Indicator RADAR.
• The system can determine moving target velocity
and to distinguish moving targets from stationary
targets.
• This RADAR uses the “Doppler effect” for its
operation.
• The basic principle of MTI RADAR is to compare
a set or received echoes with previous received
echoes and cancelling out the stationary or
permanent echoes. Whose phase remains
unchanged but moving targets will give change of
phase that’s why these are not cancelled.

38. Block Diagram of MTI RADAR

39. Blind speed
• If the target has uniform velocity, the
successive sweeps will have Doppler phase
shifts of exactly 2∏ radians and the target
appears as a stationary and gives wrong
indication.
• The speed corresponding to this condition is
called “Blind Speed”.
• The blind speed of the target is given by
Vb=PRF* nλ/2
Where n– any integer.

40. Different Types of RADARs
&
Applications

41. MIT Lincoln Laboratory
Introduction-14
AG 6/18/02
Surveillance and Fire Control Radars
Courtesy of
Raytheon. Used
with permission.
Courtesy of
Raytheon. Used with
permission.
Courtesy of
Raytheon. Used with
permission.
Courtesy of
Raytheon. Used
with permission.
Courtesy of
Raytheon. Used
with permission.
Photo courtesy of
IIT Corporation used
the permission
.
Courtesy of Global
Security. Used
with permission.
Courtesy of US
Navy.

42. MIT Lincoln Laboratory
Introduction-15
AG 6/18/02
Airborne and Air Traffic Control Radars
Courtesy of Northrop
Grumman. Used with
permission.
Courtesy of US
Navy.
Courtesy of US Air
Force.
Courtesy of US
Air Force.
Courtesy of US
Air Force.
Courtesy Lincoln
Laboratory.
Courtesy of US
Air Force.

43. MIT Lincoln Laboratory
Introduction-16
AG 6/18/02
Instrumentation Radars

44. Comparison
PARAMETER PULSE RADAR CONTINOUS WAVE RADAR
TYPE OF SIGNAL Modulated Modulated and
Unmodulated
ANTENNA Duplexer Separate Antennas
RANGE Indicates Range Don't indicate Range
TRANSMITTING POWER high Low
CIRCUIT Complicated Simple
STATIONARY TARGET Affects Doesn't affect
MAXIMUM RANGE High Low
PRACTICAL
APPLICATION
More applications Less applications
MANY TARGETS Does not get affected Does get affected