chandra shekhar_Unit 2 _Radar_ feb 4 2016

Unit 2
Radar communication
Prepared by
Chandra Shekhar K
TNTC

2.1 Explain radar working principle and Radar applications 1 Hr
2.2 List the Radar frequencies bands 1 Hr
2.3 Define pulse, Pulse width, PRF, Duty cycles, 1 Hr
2.3.1 Peak power, Average power 1 Hr
2.3.2 Simple problems 1 Hr
2.4 Write and explain the Radar range equation
Discuss the factors affecting radar range 1 Hr
2.5 Discuss Duplexer and Display systems - 1 Hr
2.5.1 and List the types 1 Hr
2.6 Explain type of Radar:
2.6.1 Pulse and 1 Hr
2.6.2 CW 1 Hr
2.6.3 FMCW 1 Hr
2.6.4 MTI 1 Hr
Syllabus

2.6.5 Secondary RADAR - IFF 1 Hr
2.7
Different landing systems ILS & GCA 1 Hr
Different landing systems ILS & GCA 1 Hr
2.8
Introduction to SONAR 1 Hr

What is radar?
 Radar is an acronym for Radio Detection and Ranging.
 It detects the presence of objects by electromagnetic energy.
 It measures the direction , height and distance of the objects
in three co-ordinates (x,y,z).
 The frequency of electromagnetic energy used for radar is
unaffected by darkness and penetrates fog and clouds to
determine the position of objects.

2.1 Radar working principle
 The radar is working under the concept of reflection of
electromagnetic energy.
 The radar signal is generated by a powerful transmitter
and antenna illuminates the target with the RF waves ,
then reflected back and received as an echo/ return
signal by a highly sensitive receiver.

Block diagram of a primary radar

Transmitter
It produces the short duration high-power RF pulses of energy
that are into space by the antenna.
Duplexer
It alternately switches the antenna between the transmitter
and receiver so that only one antenna need to be used.
This switching is necessary because the high-power pulses
of the transmitter would destroy the receiver if energy were
allowed to enter the receiver point.
Block diagram explanation

Receiver
It will analyze the received echoes and present desired
information in the suitable form.
Radar Antenna
Antenna transfers the transmitter energy to signals in space with
the required distribution and efficiency. This process is applied in
an identical way on reception.
Radar Displays
It presents the observer a continuous, easily understandable,
graphic picture of the relative position of radar

A
Applications of Radar
1. Air Traffic control
2. Aircraft Navigation
3. Ship Safety
4. Space
5. Automobile traffic measurement
6. Military

Band name Frequency range Wavelength range
HF 3–30 MHZ 10–100 m
VHF 30–300 MHz 1–10 m
UHF 300–1000 MHz 0.3–1 m
L 1–2 GHZ 15–30 cm
S 2–4 GHz 7.5–15 cm
C 4–8 GHz 3.75–7.5 cm
X 8–12 GHz 2.5–3.75 cm
KU 12–18 GHz 1.67–2.5 cm
K 18–24 GHz 1.11–1.67 cm
Ka 24–40 GHz 0.75–1.11 cm
mm 40–300 GHz 7.5 mm – 1 mm
2.2 Radar Frequency bands

2.3 Define of pulse related terms
Pulse width:
The duration for which transmitter is on is called Pulse-width.
Pulse Repetition frequency (PRF):
Rate of transmission of consecutive pulses or number of
consecutive pulses transmitted per second is called Pulse
Repetition frequency.
Pulse Repetition interval (PRI):
Time duration between onset of two successive pulses is called
pulse repetition interval.
Duty cycle:
It is the ratio of pulse width to the pulse repetition interval.

2.3.1 Peak power , Average power
Peak power:
The power produced by the transmitter during pulse width
is known as peak power of the transmitter.
Average power:
Average power is the power transmitted over the one PRI.
Its typical values are ranging from 50 to 300 watts.

2.4 Radar Range Equation
Radar Range equation is an interesting tool for
the Radar system design .
It is an important relation between range of the
target & characteristic parameters of various
components that forms Radar .
Radar Range equation is given by
4/1
min
4max
)4(






×= ec
t
AGA
p
P
r
π

2.4 Radar Range Equation
parameters.
4/1
min
4max
)4(






×= ec
t
AGA
p
P
r
π
Where,
Pt = Transmitted power in watts.
G = Antenna Gain
Ae = Antenna effective aperture
Ac = Radar cross section.
Pmin = minimum detectable signal

Factors affecting the Radar Range:
1. Transmitted power.
2. Antenna Gain
3. Antenna effective aperture
4. Radar cross section.
5. Minimum detectable signal

2.5 Duplexer
Duplexer
It alternately switches the antenna between the transmitter and
receiver so that only one antenna need to be used.
This switching is necessary because the high-power pulses of the
transmitter would destroy the receiver if energy were allowed to
enter the receiver point.

2.5.1 Types of Display systems
Radar can be classified into different types depending on
their application & requirement , they are:
1. Based on Video Display system
a. Raw Video display systems
b. Synthetic video display systems
2. Based on operating conditions:
a. Conventional CRT
b. Direct View storage tube
3. Based on CRT display
a. A-scope d. D-scope
b. B-scope e. E-scope
c. C-scope
4. Plan position Indicator display

The PPI display provides a 2-D "all round" display of
the airspace around a radar site. The distance out from the
center of the display indicates range, and the angle around
the display is the azimuth to the target.
Plan Position Indicator

2.6.Types of Radar
1. Pulse Radar
2. Continues wave Radar
3. FMCW
4. MTI
5. Secondary Radar

2.6.1 Pulse Radar block diagram
Synchronizer Transmitter
Display Unit Receiver
Power
Supply
ANT.Duplexer
RF
Out
EchoIn
Antenna Control

1. Synchronizer:
a. Coordinates the entire system
b. Determines the timing of the transmitted pulse
c. Includes timers, modulator and central control.
2. Transmitter:
a. Generate the pulse (RF) at the proper frequency and
amplify.
3. Antenna:
A. Receives energy from the transmitter, radiates it in the
form of a highly directional beam.
B. Receives the echoes for pulse radars.
Explanations

4. Duplexer:
a. Allows one antenna to be used to transmit and receive.
b. Prevents transmitted RF energy from going directly to the
receiver.
c. Tells the antenna to radiate or receive.
5.Receiver: receives incoming echoes from antenna, detects
and amplifies the signal, and sends them to the display.
6. Display: Displays the received video to the operator.
7. Power Supply: Provides power to all the components of the
system.

Special purpose RADARS
Special purpose RADARS:
RADARS which are used for special purpose such as to find
Relative velocity of the targets is called Special purspose
Radars.
Types of Special RADARS:
1. CW Radar
2. FMCW Radar
3. MTI Radar
All the above RADARs are based on application of Doppler
Effect.

Doppler effect
Statement:
“The apparent frequency of electromagnetic waves
depends on the relative radial motion of the source
and observer . If the source and observer are
moving away from each other , the apparent
frequency will decrease. If they are moving towards
each other, the apparent frequency will increase.”
This is called Doppler effect.
Doppler shift is given by
Fd= (2Vr)/λ

Doppler Frequency Shifts
Motion Away:
Echo Frequency Decreases
Motion Towards:
Echo Frequency Increases

Example of Doppler effect
The radars (Special purpose RADARs) works on the Doppler
effect principle .
If the aircraft approaches radars and moves away from the
radar, correspondingly frequency of reflected signal will
increase or decrease than the actual transmitted frequency
i.e, speed of moving objects alters the EM frequency .
The difference in transmitted frequency and reflected
frequency is called doppler shift frequency (fd)

2.6.2 Continuous Wave Radar
 Employs continual RADAR
transmission
 Separate transmit and
receive antennas
 Relies on the “DOPPLER
SHIFT”

Block Diagram
Discriminator AMP Mixer
CW RF
Oscillator
Indicator
OUT
IN
Transmitter Antenna
Antenna

Amplifier. Increases strength of signal before sending it to the
indicator.
Discriminator.
a. Selects desired frequency bands for Doppler shifts,
eliminates impossible signals.
b. The unit will only allow certain frequency bands so won’t
process stray signals.
Indicator.
Displays data. Displays velocity or the component
directly inbound or directly outbound. Range is not measured

Fm
Transmitter Modulation
Mixer Amplifier Limiter Frequency
counter
Indicator
Receiving antenna
Transmitting antenna
Reference signal
2.6.3 FMCW

2.6.3 FMCW
CW radars have the disadvantage that they cannot measure
distance, because it lacks the timing mark necessary to allow
the system to time accurately the transmit and receive cycle
and convert the measured round-trip-time into range.
In order to correct for this problem, phase or frequency
shifting methods can be used. In the frequency shifting
method, a signal that constantly changes in frequency around
a fixed reference is used to detect stationary objects and to
measure the rage

In the frequency shifting method, a signal that constantly
changes in frequency around a fixed reference is used to detect
stationary objects and to measure the rage.
In Frequency-Modulated Continuous Wave radars (FMCW), the
frequency is generally changed in a linear fashion, so that there is
an up-and-down or a saw tooth-like alternation in frequency.
If the frequency is continually changed with time, the frequency
of the echo signal will differ from that transmitted and the
difference Δf will be proportional to round trip time Δt and so the
range R of the target too.

When a reflection is received, the frequencies can be
examined, and by comparing the received echo with the
actual step of transmitted frequency, you can calculate
range
Advantages:
1.There is no limit on the minimum range.
2.Simple low power equipment can be used.
3.Small antennas can be used to reduce the size of the
equipment.

2.6.4 MOVING TARGET INDICATOR
(MTI) RADAR

Introduction
It is possible to remove clutter (echoes from stationary
targets) from the radar display and show only the moving
targets.
MTI Radar is capable of measuring the range and radial
velocity of moving targets even in the presence of strong
clutter.
The range is measured on the basis of time lapse between
the transmitted signal and recived echo.
Velocity of moving targets is measured on the basis of
Doppler shift imparted to the transmitted signal.

1. Coho(Coherent Oscillator):
It is a stable oscillator whose frequency is same as
intermediate frequency used in the receiver (Fc=Fi).
In addition to providing the reference signal, the output of
the coho (Fc) is mixed with the local oscillator frequency
(Fo) in the transmitter mixer to produce RF signal
(Fs=Fc+Fo).
2. Stalo (Stable Local oscillator):
The function of stalo is to provide necessary frequency
translation in the transmitter as well as receiver.
The transmitter mixer converts IF to RF (Fs=Fc+Fo).
In the Receiver mixer, RF echo Fs is heterodyned with the stalo
signal Fo to produce the IF signal.

3. Power Amplifier:
Power amplifier such as Klystron are most commonly used to
amplify the RF signal produced by the transmitter mixer. The
waveform amplified by the power amplifier travels to the
antenna through duplexer via a transmission line, where it is
radiated into free space.
4. Modulator:
The power amplifier is “pulsed” (turned on or off ) by the
modulator to generator a repetitive train of pulses.
5. Duplexer:
A single antenna is generally used for both transmitting and
receiving. The function of the duplexer is to protect the
receiver from damage caused by the high power from
transmitter.

6. Phase Detector:
The inputs to the phase detector are Fc and Fi. Its output is a voltage
proportional to the phase difference between the two input signals. Since
the output of this detector is phase sensitive, the phase difference between
the transmitted and recived signals will be constant for fixed targets.
But it will vary for moving targets due to Doppler shift. The output of the
phase detector is used for producing the video signal.
7. Video:
 The output of phase detector and delay line are amplified to suitable level
by Amplifier 1 and Amplifier 2 respectively before applying to subtractor.
 Subtractor compares received echo with that received during the previous
scan.
 For stationary targeget result will be zero hence no display.
 For moving targets it produces butterfly effect on the A scope indicator.

If the target happens to have a velocity whose radial
component results in a phase difference of exactly 2π rad
between successive pulses,the target thus appears
stationary. Echoes from it are canceled by the MTI action.
A radial velocity corresponding to this situation is known as a
blind speed.
This can be mathematically expressed as
Vb=(PRF * nλ)/2
Where Vb= Blind speed
λ= Wavelength of transmitted signal
n= any integer including 0
Blind Speeds

2.6.5 Secondary radar
The RADARS discussed in previous sections, Pulsed Radar, CW
Radar ,FMCW radar and MTI Radars are classified as Primary
Radars.these RADARs are used for detection, ranging or velocity
measurements. Transmitter and receiver frequencies are the same
because Radar operation depends on echo.
Secondary radars are also called as Secondary Surveillance
Radar(SSR).
It is used for identification . It differs from the primary radar in the sense
that it does not make use of reflection of the transmitted energy.
A typical IFF system of SSR is as shown below,

IFF system explanation
IFF stands for Identify Friend or Foe
In a SSR system, pulse transmission from ground is
received at the target such as an aircraft.
It is detected and decoded in the aircraft transponder
(beacon) shown in figure b.
The aircraft transponder then transmits coded pulses back
to ground after a certain known delay. Thus identify of the
aircraft can be established on ground.

Applications
Used in air traffic control (ATC)
Used for Military purposes.
To track aircraft

2.7 Different landing systems ILS
& GCA
Introduction:
While landing, the aircraft has to take a path in line with the
runway.
when the visibility is good, landing operation is carried out
by visual observation of ground and landing lights.
when the visibility is poor, help of Landing instruments is
taken.
Landing instruments provide information about horizontal and
vertical deviation of the aircraft.
Two types of landing aids are commonly used:
1. Instrument Landing system (ILS)
2. Ground Controlled approach (GCA)

 It is a ground-based instrument approach system that
provides precision guidance to an aircraft approaching and
landing on a runway,
Instrument landing system (ILS)
Typical ILS system

ILS Explanations
ILS comprises of the following 3 units:
1.Localizer:
 It gives a vertical equisignal plane which passes through
centre line of the runway.
 It is located at about 300 meters from the end of runway.
 It operates in the VHF band (108-112 MHz).
 When the aircraft is flying along the correct path, the
meter remains in the centre.
 If the aircraft deviates , the indicator bar on the panel
meter shifts in direction accordingly so that corrective
action can be taken.

2. Glide slope:
 It gives an equisignal plane inclined to the horizontal at
the desired angle of descent which generally lies
between 2 degree to 5 degree.
 This system operates at about 330 MHz.
 Transmitter of glide slope is located on one side of the
runway near the touch down point at a sufficient
distance.
 The intersection of two equisignal paths provided by the
localizer and the glide scope gives the approach path.

3. Marker Beacons:
 Are used to indicate the position of the aircraft along the
localizer path from the touch down point.
 Three beacons operating at 75 MHz are used for each
runway.
 Outer marker is located at about 8-10km from the touch
down point of runway. Middle marker is located at about
1km from touch downpoint. Inner marker is placed at
about 60 meters from touch downpoint.
 In the aircraft , a single receiver is used to receive the
marker signals and the output is available as an audio
tone as well as three lamps with colour code.

Ground-controlled approach
Ground-controlled approach is the oldest air traffic
technique to fully implement radar to service a plane - it was
largely used during the Berlin airlift in 1948-49.
This approach is runway navigational aid for the aircraft
landing in the low or zero visibility and ceiling conditions.
It consists a ground based radar system, having two
separate radars; one for searching aircraft & other for
tracking it.

The two separate radars are a surveillance radar element
(SRE) and other precision approach radar (PAR).
SRE: to locate and identify the approaching aircraft before it
is acquired by the PAR for tracking.
PAR: it keeps track of aircrafts parameters like azimuth,
elevation and range
.

1. An aircraft to be landed with this system is first
brought into the proper position for starting its descent
by means of surveillance radar.
2. A controller at the indicators of PAR set then takes
over.
3. Instruction to pilot must be done through glide path
4. If for any reason, the aircraft cannot be talked through
proper glide path ,it is instructed to discontinue the
landing and turn back for a second attempt.
Procedure of aircraft landing:

2.8 Introduction to SONAR
Sound Navigation And Ranging (SONAR)
– Sound pulses emitted reflected off metal objects with
characteristic ping
– Like Radar and Lidar time of flight is measured to
determine distance
– Early sonar gave only distance and direction to target
– Modern sonar used for mapping

Principles of SONAR
 Sound waves are a mechanical vibration
Can only travel through an elastic medium (air, water,
earth)
 Measured by frequency instead of wavelength (λ)
How is frequency related to λ?

Types of SONAR
1.Single beam SONAR
2.Multi beam SONAR

Problems:
1. Calculate the dutycycle of radar if the pulse width is 1µs
and TRF is 500pps.
Solution:
Given data Pulse width = 1µs ; TRF= 500 pps
We know that,
1.PRI=1/(TRF);
therefore substituting we get
PRI=1/(500)= 2ms
2. Duty cycle =(Pulse width )/ (PRI)
therefore substituting we get
Duty cycle =(1* 10^-6 )/ (2*10^-3) = 0.5
Result : Duty cycle for a given RADAR is 500µ

Problems:
2. Calculate the dutycycle of radar if the pulse width is 20µs
and TRF is 1000pps.
Procedure is same as 1st
Problem
Result : Duty cycle for a given RADAR is 20m

Problems:
3. Calculate the Maximum range of a radar system which
operates at 3cm with a peak pulse power of 500kW, if its
minimum receivable power is 10^-13 W, the capture area of
its antenna is 5meter square and the cross-sectional area of
the target is 20meter square.
Solution:
List out given data
Substitute in Radar range equation formula
Result:
Maximum range of Radar is found to be 685.68 Km

Reference Books:
1. Introduction to Radar Systems - M.I. Skolnik
2. Radar, Principles,Technology, applications – BYRON
EDGE
3. Electronic communication systems – George Kennedy
4. Advanced communication system- Veeranna

chandra shekhar_Unit 2 _Radar_ feb 4 2016

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