RADAD ENGINEERING

M.VAMSHI KRISHNA

ASST PROF

DEPT OF ECE

RADAR

ENGINEERING

• Radar is an electromagnetic device and it

is a powerful electronic eye.

• RADAR represents means RAdio,

Detection And Ranging.

Radar can see the objects in

• day or night

• rain or shine

• land or air

• cloud or clutter

• fog or frost

• earth or planets

• stationary or moving and

• good or bad weather.

In brief, Radar can see the objects hidden any

where in the globe or planets except hidden

behind good conductors.

INFORMATION GIVEN BY THE

RADAR

Radar gives the following information :

• The position of the object

• The distance of objects from the location of radar

• The size of the object

• Whether the object is stationary or moving

• Velocity of the object

• Distinguish friendly and enemy aircrafts

• The images of scenes at long range in good and adverse weather conditions

• Target recognition

• Weather target is moving towards the radar or moving away

• The direction of movement of targets

• Classification of materials

APPLICATIONS OF RADARS

Radars have a number of applications for domestic, civilian and military purposes. In particular, radar is used

• To indicate speed of the automobiles, cricket and tennis balls etc.

• To control guided missiles and weapons

• To provide early warning of enemy

• To aircrafts, ships, submarines and spacecrafts for defence purposes

• For weather forecast

• For remote sensing

• For ground mapping

• For airport control

• For airport surveillance

• For precise measurement of distances for land surveying

• To detect and measure objects under the earth

• For navigating aircrafts and ships and submarines in all the weather conditions and night.

• To detect and locate ships, land features and sea conditions to avoid collision

• To map the land and sea from aircrafts and spacecrafts

• To study the nature of stars and planets

• To measure altitude from the earth for aircrafts and missile navigation etc.

• For searching of submarines, land masses etc.

• For bombing aircrafts, ships and cities in all weather conditions

• To aim at enemy air crafts, ships and locations.

NATURE AND TYPES OF RADARS

RADAR FREQUENCY BANDS

The IEEE standard radar frequency bands are given in table

Band NameFrequency Range

(GHz)Wavelength Applications

mm 40 – 300 7.5 – 1 mm Radar experiments

ka 27 – 40 1.11 – 7.5 mm

Satellite communication, radars microwave labs etc

k 18 – 27 1.67 – 1.11 cm

ku 12 – 18 2.5 – 1.67 cm

X 8 – 12 3.75 – 2.5 cm

C 4 – 8 7.5 – 3.75 cm

S 2 – 4 15 – 7.5 cm

L 1 – 2 30 – 15 cm Television, satellite, navigation aids UHF 0.3 – 1 1 – 30 cm

VHF 0.03 – 0.3 10 – 1 mTelevision, satellite

communication, FM broadcast police radio

HF 0.003 – 0.03 100 – 10 m telephone

LIMITATIONS

• Radar can not recognize the color of the targets.

• It can not resolve the targets at short distances like human eye.

• It can not see targets placed behind the conducting sheets.

• It can not see targets hidden in water at long ranges.

• It is difficult to identify short range objects.

• The duplexer in radar provide switching betweenthe transmitter and receiver alternatively when acommon antenna is used for transmission andreception.

• The switching time of duplexer is critical in theoperation of radar and it affects the minimumrange. A reflected pulse is not received during

• the transmit pulse

• subsequent receiver recovery time

• The reflected pulses from close targets are notdetected as they return before the receiver is

connected to the antenna by the duplexer.

RANGE EQUATION OF BASIC RADAR

• Radar range equation gives a relation for

the maximum radar range in terms of

transmitter power, effective area of the

antenna, radar cross-section, wavelength,

minimum detectable signal, and gain of

the antenna.

• Radar range equation is

41

min2

2et

maxs4

ApR

In the above equations,

= transmitter power (watts)

G = maximum gain of the antenna (no units)

= effective area of the receiving antenna

= Radar cross-section of the target = Maximum

range of the radar (m)

= Minimum detectable signal

= Minimum detectable signal

41

min23

22t

maxs4

GpR

tp

eA

maxR

2m

2m

mins

TYPES OF BASIC RADARS

• Monostatic and Bistatic

• CW

• FM-CW

• Pulsed radar

MONOSTATIC RADARS• Monostatic radar uses the antenna for transmit and

receive.

• Its typical geometry is shown in the below fig.

Fig. Monostatic radar

Antenna

Target

Monostatic Radar Equation

• The monostatic radar equation is given by

If represents transmitter losses

represents receiver losses

represents medium losses

mrt43

M22

tR

LLLd4

Gpp

43

M2

ttR

d4

Gpp

tL

rL

mL

BISTATIC RADAR

• Bistatic radars use transmitting andreceiving antennas placed in differentlocations.

• CW radars in which the two antennas areused, are not considered to be bistaticradars as the distance between theantennas is not considerable.

• The bistatic radar geometry is shown inbelow fig.

Fig. Bistatic radar geometry

Antenna

Target

Antenna

Bistatic Radar Equation

• If represents transmitter losses,

represents receiver losses and represents

medium losses.

mrt2r

2t

3

B2

rttR

LLLdd4

GGpp

rL mLtL

THE PULSED RADAR

• A simple pulsed radar is shown in below fig.

Fig. Simple pulsed radar

RF Pulse

Pulsed Radar Equation

Here, = bandwidth correction factor.

= noise temperature

4

1

Bfon2

42rtt

maxLCVTk4

CGGpR

BfC

nT

The Block Diagram of Pulsed

Radar

• The diagram of pulsed radar is shown in

below fig.

Fig. Block diagram of pulsed radar

Synchronizer ModulatorHigh

Frequency Oscillator

Duplexer

Display Unit

Video Amplifier Detector

IF Amplifier

Mixer Local Noise

RF Amplifier

Local Oscillator

MEASUREMENT OF RANGE

WITH PULSED RADAR

• The measurement of range on the CRT by pulsed radar

is made from the leading edge of the transmitted pulse to

the leading edge of the received echo. (below Fig.).

Fig. Measurement of range

Range

• The Measurement of range by pulsed radar involves themeasurement of time taken for an electromagnetic waveto travel towards a target and back to the radar.

• Velocity of electromagnetic wave =

• or velocity of electromagnetic wave =

• Velocity of electromagnetic wave = 0.3 km/s

• It is obvious from the above data, there exists a timeinterval of 2 × 3.333 = 6.666 s between the pulseleaving the transmitter towards a target and echo arrivingback to the radar for every kilometer.

• The range is therefore given by

• Range (in km) = (0.15) × time interval between the

transmission and return of echo in

microseconds

s/m300

s/m103 8

APPLICATION OF PULSED

RADAR

The pulsed radar is used to find the target’s

• range

• bearing and elevation angle

• height

CONTINUOUS WAVE (CW)

RADAR

• CW radar detects objects and measures

velocity from Doppler shift.

• It can not measure range.

• It can be monostatic or bistatic.

The Doppler Effect

• The Doppler Effect was discovered by

Doppler.

• Doppler is Austrian mathematician.

Principle of Doppler Effect

• The radars radiate electromagnetic waves towards thetargets for detection and also to obtain details of thetarget.

• When the target is stationary, the frequency of thereceived echoes is constant.

• However, when the target is moving, the frequency ofthe received echoes are found to be different fromtransmitted frequency.

• If the target approaches the radar, the frequency isincreased and if the target moves away from the radar,the frequency is decreased.

• That is, in the moving targets, there exists a frequencyshift in the received echo signals.

• The presence of frequency shift in the received echo

signals in the radar due to moving targets is known as

Doppler effect.

• The frequency shift is known as Doppler frequency shift

and it is given by

Here, = Doppler shift frequency, Hz

= transmitter frequency, Hz

= velocity of the target, m/s

= velocity of electromagnetic waves in free

space

o

o

td f

2f

df

oft

o

• The Doppler Effect is shown in below fig.

CW Radar

CW Radar

Aircraft moving towards the radar

radar

Aircraft moving away from the

radar

dor fff

dor fff

of

of

Fig. Doppler Effect

m

kts

m

kts03.1Hzf tt

d

tIf is expressed in knots, the Doppler shift frequency is given by

• A simple CW radar is shown in below fig.

Fig. CW radar using Doppler Effect

• The CW radar consists of a transmitter, mixer,accurate frequency measuring device anddisplay unit.

CW Radar Transmitter

Mixer Accurate

Frequency Measuring Device

Display Unit

Transmitter

• The transmitter emits continuouselectromagnetic waves towards the targets.

• A single antenna is used for transmission andreception. The duplexer is used to isolate thereceiver from high transmitter power.

• For radar approaching targets, the reflectedsignal frequency is high than the transmitterfrequency. for moving away targets from radar,the reflected signal frequency is lower than thetransmitter frequency.

• That is,

for incoming targets

for moving away targets

Here, = frequency of reflected signal

= frequency of transmitted signal

= Doppler shift frequency

dtr fff

dtr fff

rf

tf

df

Mixer

• The transmitted signal of frequency and

reflected echo signal of frequency are

given as input to the mixer.

• The output of the mixer is Doppler

frequency signal.

Accurate Frequency Measuring

Device

• The output of the mixer is given to an

accurate frequency measuring device to

find out the radial velocity of the target.

Display Unit• The output of the mixer is given to the display

unit.

• This indicates the presence of moving target.

• In the case of stationary target, the Doppler shiftfrequency is zero.

• That is, the transmitted frequency and reflectedecho signal frequency are the same.

• In the case of moving targets, the Doppler shiftfrequency is very small compared to transmitterfrequency.

• Sometimes, it is difficult to recognize thisfrequency. however, such as small frequency ismeasured using superhetrodyne principle.

BLOCK DIAGRAM OF CW DOPPLER

RADAR• The detailed block diagram of CW Doppler Radar is

shown in below fig.

Fig. Detailed block diagram of CW Doppler radar

Transmitter

Mixer 1

IF Amplifier

Local Oscillator

Mixer 3

Mixer 2

IF Amplifier 2Frequency

Discriminator

Display

Receiving Antenna

Transmitting Antenna

MEASUREMENT OF VELOCITY

OF TARGET

• The velocity of the moving object is determined

by

Here, = velocity of the target

= Doppler shift frequency

= transmitter frequency

= free space velocity of EM wave

2f

f o

t

dt

t

df

tf

o

MEASUREMENT OF BEARING AND

ELEVATION ANGLES OF THE TARGET

• The transmitting antenna focuses the radar waves andradiates them in the shape of the beam.

• The beam is pointed directly at the target in free space.The receiver antenna picks up the maximum signal whenit is pointed directly at the reflecting target.

• The received echo signal is maximum when both thetransmitting and receiving antennas are pointed directlyat the target.

• The position of the radar antenna corresponding to themaximum received echo signal represent bearing andelevation angles of the target which is in the path of thebeam.

• A typical example is shown in below fig.

Fig. Measurement of bearing and elevation of a target

N

S

W

Range

Elevation Angle,

Azimuth Angle,

E

APPLICATIONS OF CW RADAR

The CW radar is used to find the targets

• bearing angle

• elevation angle

• velocity and

• to indicate the presence of moving targets

• radial velocity of moving targets

• whether an object is approaching or moving away

DISADVANTAGES OF CW

RADAR

• The CW radar does not give range

information

CW RADAR EQUATION• The range equation of CW radar is given by

Here, = CW average transmitted power over the

dwell interval

=

= Target illumination time

G = antenna gain

R = Range of target from radar

k = Boltzman constant =

= Effective noise temperature

F = Noise figure

L = Radar losses

We43

22dCW

LLFTkR4

GTpSNR

avp

)say(pCW

iT

eT

k/J1038.1 23

FMCW RADAR

• FMCW radar detects, measures range andradial velocity of objects.

• An FM CW Radar is a FrequencyModulated Continuous Wave radar inwhich the frequency of continuouslytransmitted wave is varied at a known rateand the frequency of reflected signals iscompared with the frequency of thetransmitted signal.

• A simple FMCW radar is shown in below fig.

Fig. Frequency modulated CW radar

BLOCK DIAGRAM OF FMCW

RADAR

• The block diagram of FMCW radar is shown in below fig.

Fig. Block diagram of FMCW radar

Frequency Generator

Frequency Modulator

FM Transmitter

MixerAmplifier Limiter

Frequency Clutter Display

APPLICATIONS

FMCW radar is used to measure

• Slant range of the target

• Bearing and elevation angles of target

• Height of the target

PULSED DOPPLER RADAR

• Radar with high PRFs is called pulsed

Doppler radar.

• It contains pulse and CW radars.

• It operates at high PRF to avoid the

problems of blind speeds.

TYPES OF PULSED DOPPLER

RADAR

They are

• MTI with many Doppler ambiguities and

without no range ambiguities.

• The pulsed Doppler radar with high PRF,

many range ambiguities and without

Doppler ambiguities.

• The pulsed Doppler radar with some range

ambiguities and Doppler ambiguities.

BLOCK DIAGRAM OF PULSED

DOPPLER RADAR

• It is shown in below fig.

Fig. Block diagram of pulsed Doppler radar

Locking Mixer Transmitter Doppler

COHO STALO Receiver Mixer

Processor Phase Detector IF Amplifier

Display

APPLICATIONS

• Weather warning

• Detection of the target and estimation of

target motion.

ADVANTAGES OF PULSED

DOPPLER RADAR

These are

• It is able to reject unwanted echoes with

the help of Doppler filters.

• It is able to measure the range and

velocity even in the presence of multiple

targets.

• Signal-to-noise ratio is high.

NAVIGATION RADARS

• Navigation radars are also in the category

of surface search radars.

• Helps pilots in the navigation of aircrafts

and ships.

• Its operating range is small

• It has high resolution than surface search

radars.

SURVEILLANCE (SEARCH)

RADAR

• The search radars scan the radiation

beam continuously over a specified

volume in space for searching the targets.

• The search radars determines range,

angular position and target velocity.

SEARCH RADAR EQUATIONThe search radar equation is given by

Here, = Average power

=

=

= Duty cycle

PW = Pulse width

PRF = Pulse repetition frequency

A = Aperture area

=

D = Aperture diameter

= Radar cross-section

= Scan time

= Search volume

k = Boltz man constant = = Effective noise temperature, Kelvin

F = Noise figure

L = Radar losses

LFTkR4

TApSNR

e4

seav

avp PRFPWpt

ct dp

cd

4

D4

MTI RADAR

Meaning of MTI Radar• MTI radar means Moving Target Indication radar.

• This is one form of pulsed radar.

• MTI radar is characterized by its very low pulse repetition frequency

and hence there is no range ambiguity in MTI radar.

• The unambiguous range is given by

Here, = pulse repetition frequency

= velocity of electromagnetic wave in free space

• At the same time, MTI radar has many ambiguities in the Doppler

domain.

• It determines target velocity and distinguishes moving targets from

stationary targets.

p

oun f

R

pf

o

BLOCK DIAGRAM OF MTI RADAR

• The block diagram of MTI radar is shown in below fig.

Modulator

Microwave Signal Amplifier Duplexer

STALO

COHO

Mixer 2

IF Amplifier

Phase Detection

Delay Line Cancellation

Display Unit

Amplifier 1

Subtractor

Mixer

Amplifier 2

MTI Output

Fig. Block diagram of MTI radar

cff

dc fff

dc ff

df

pf/1T

cf

f

cff

BLIND SPEEDSDefinitions

• Definition 1 : Blind speed is defined as the radialvelocity of the target at which the MTI response is zero.

• Definition 2 : It is also defined as the radial velocity ofthe target which results in a phase difference of exactly2 radians between successive pulses.

• Definition 3 : Blind speed is defined as the radialvelocity of the target at which no shift appears makingthe target appears stationary and echoes from the targetare cancelled.

Definition 4 : The blind speed of the target is defined as

Here, = blind speed

= pulse repetition frequency

n = any integer = 0, 1, 2, 3, . . .

= wavelength

= pulse repetition interval

The first blind speed in knots is given by

The other blind speeds are integer multiples of . The blind speeds are serious limitation in MTI radar.

p

pbT2

n

2

nf

b

pf

pT

Hzfm

Hzfm97.0knots

p

p1b

METHODS OF REDUCTION OF EFFECT

OF BLIND SPEEDS

There are four methods to reduce the effect

of blind speeds by operating the radar at

• long wavelengths

• high pulse repetition frequency

• more than one pulse repetition frequency

• more than one wavelength

MST RADAR

Meaning of MST Radar

• MST radar represents Mesosphere, Stratosphere andTroposphere radar.

• The MST radar is one type of wind profiler designed tomeasure winds and other atmospheric parameters up toaltitudes of 100 km or more.

• Mesosphere is the atmospheric region between 50 – 100km above the earth.

• Stratosphere is the atmospheric region between 10 – 50km above the earth.

• Troposphere is the atmospheric region between 0 – 10km above the earth.

SYNTHETIC APERTURE RADAR (SAR)

• SAR is a radar which moves the antenna beam across

an area to synthesize a very large aperture.

• It provides excellent angle and cross range resolution.

• SAR uses a technique which synthesizes a large

antenna with a small antenna by examining the volume

of interest sequentially.

• The length of the synthetic antenna aperture is given by

Here, D is horizontal dimension of physical antenna

R is maximum length of synthetic aperture

is the operating wavelength

D

RL off

Salient Features of Synthetic Aperture Radars

• It synthesizes very large apertures.

• It provides excellent angle and cross range resolutions.

• In these systems, radars moves rapidly and the targetsare stationary.

• It is also useful where the radar is stationary and thetargets move rapidly.

• It synthesizes a large antenna with a small real antennasystematically examining a large volume.

• If the radar is stationary and the targets move rapidly,the above system is known as inverse SyntheticAperture Radar (SAR).

• ISAR is used to analyze formatting of aircraft fromground base or shipborn radars.

• ISAR is used to find how many aircrafts are in theformation.

• ISAR is also diagnostic radar which analyzes thescattering of targets to reduce their radar reflectivity.

• SAR is used in remote sensing and mapping.

• SAR is also used to obtain a map like display from the image of earth’s surface.

• The imaging map by SAR is useful for military reconnaissance.

• It is used for weapon targeting.

• SAR is also used for geological and mineral explorations.

• SAR was first used by NASA, USA.

• SAR mapping is similar to that the Doppler Beam Sharpening (DBS).

• SAR provides two-dimensional image of a target in range and cross range.

• SAR produces images scenes at a ling range and in adverse weather.

• SAR has a theoretical cross range equal to , being the horizontal dimension of the antenna.

• SAR does not provide images of moving targets accurately.

• SAR images of moving targets are distorted and displaced from the pitch.

• The concept of synthetic aperture radar is

shown in below fig.

Target x

Target y

Target z

Effective length of SAR antenna

Fig. Concept of SAR

Target x

Target y

Target z

Effective length of real antenna n

• The design of SAR waveforms is made bysatisfying the following inequality.

Here, is velocity of the source

R is the range of the target

PRF is pulse repetition frequency

d is the aperture of the incremental radiator

is free space velocity of electromagnetic

wave

This condition avoids range and velocity ambiguity.

R2PRF

d

2 o

o

SYNTHETIC APERTURE RADAR EQUATION

• The single pulsed radar equation is given by

Here, = Peak transmitter power

G = Antenna gain

= Wavelength

= Radar cross-section

= Slant range of ith bin

k = Boltzman’s constant =

B = Receiver bandwidth

L = Radar losses

= Effective noise temperature

LBTkR4

GpSNR

e4i

3

22t

tp

iRk/J1038.1 23

eT

APPLICATIONS OF SAR

• SAR is used for remote sensing and ground mappingpurposes.

• It is used for military reconnaissance.

• It is used for determining sea state and ocean waveconditions.

• It is used for geological and mineral explorations.

• It is used to obtain two dimensional image of targets.

• It is used to produce images of scenes at ling rangesand in adverse weather.

• It is used to obtain excellent angle and cross rangeresolutions.

• SAR images provide information about ice, floods, earthcontents, resource prospects, land use, crop quality,snow fields, inventory, industrial distributions, forestry,deserts, buildings and hills etc.

DISADVANTAGES OF SAR

• It does not provide the images of moving

targets.

• SAR images of moving targets are

distorted and displaced from the pitch.

MONOPULSE TRACKING

RADAR

• Monopulse tracking radar is a radar in

which the information about angle error is

obtained on a single pulse.

• This is also called as simultaneous lobing.

• The monopulse angle measurement is

done by several methods.

• The amplitude comparison monopulse

method is most popular.

Amplitude Comparison Monopulse

Tracking Radar

• The block diagram of amplitude comparison monopulse

tracking radar is shown in below fig.

• This is used for the measurement of single angular

coordinate of the target.

Fig. Block diagram of amplitude comparison monopulse

tracking radar for a single angle coordinate

measurement

Transmitter TR Mixer 1 IF Amplifier Amplitude Detector

LO

Mixer 2 IF Amplifier 2

Phase Detector

Display Hybrid Junction

Difference Channel

Range Signal

Angle Error Signal

Sum Channel

PHASE COMPARISON

MONOPULSE RADAR SYSTEM

• The phase comparison monopulse radar is also calledInterferometer radar. In this method, two antenna beamslooking in the same direction are used.

• Here, the amplitudes of the signals are the same withdifferent phases. The phase difference in the two signalsreceived by the two antennas is given by .

• Here, is wavelength, d is the spacing between the twoantennas, is the direction of arrival of signal withrespect to normal to the baseline. The pulse comparisonmethod used in one angle coordinate is shown in belowfig. It consists of two antennas producing identicalbeams.

sind

2

Fig. Phase comparison method

d

1 2

Bore site

ADVANTAGES OF PHASE COMPARISON

MONOPULSE RADAR

• The scanning of radiation beams and

beam shaping are very fast.

DISADVANTAGES

• It is less efficient than the amplitude comparisonmethod.

• It has the effect of grating lobes due to spacingof the two antennas.

• It is less popular method.

• Only one-fourth of the available antenna area isused for transmitting and only one-half the areais used while receiving, to obtain each anglecoordinate.

• When the spacing between the antennas isgreater than the antenna diameter, the sidelobesin the radiation patterns are high and EMI isproduced.

SEQUENTIAL LOBING RADAR

• In sequential lobing, only one beam is switchedbetween two squinted sequential angularpositions for target-angle measurement.

• This method is called sequential lobing.

• It is also called sequential switching or lobeswitching.

• Here, time sharing is done in using singleantenna beam.

• The method is simple and requires lessequipment and cost effective.

• But it is not very accurate.

• An antenna and its lobe which is switched

sequentially between X and Y directions is

shown in below fig..

Fig. Sequential lobing in polar coordinates

X Y

Target

ADVANTAGES OF SEQUENTIAL

LOBING

• It requires only one antenna

• Operation is simple

• It requires less equipment

• It is cost affective.

DISADVANTAGES

• It is not very accurate.

CONICAL SCAN TRACKING

RADAR

• The conical scan tracking radar is a radar

in which the squinted beam is continuously

rotated to obtain angle measurements in

two coordinates for tracking the target.

• The conical scan is also simply called

con-scan.

MAIN FACTORS AFFECTING RADAR

OPERATION

The radar operation is affected by several factors. These are

• the external man-made EMI

• the electromagnetic interference coming from other transmitters

• EMI generated within the receiver

• signals reflected by natural phenomenon like rain, fog, and cloud etc.

• the electromagnetic interference due to natural sources like lightening, solar and cosmic radiations.

• signals reflected by clutter land masses, buildings and hills.

• the curvature of the earth

• noise produced within the receiver

• the peak transmitter power

• average power

• sensitivity of the receiver

• antenna efficiency

• antenna beam shape

• sidelobes of radiation pattern

• beamwidth of antenna pattern

• radar cross-section of the target

• ambient temperature

• radar location

• type of earth at the location of the radar

• size of the target

• shape of the target

• polarization of the radar antenna

• the medium between the radar and the target

• radar pulse width

• pulse rest time

• the time interval between pulses

• frequency of operation

• signal to noise ratio

NOISE GENERATED WITHIN THE RECEIVER

• When the noise in the radar receiver is high, the echosignal will be masked.

• The noise can be made minimum by reducing thebeamwidth.

• Typical low noise receiver and its output are shown in below fig.

Fig. Receiver output with low noise

Receiver

External Noise

Amplified Echo Signal

Amplified Internal Noise

External Amplified Noise Echo Signal

• At the same time, high noise receiver and

its output are shown in below fig.

Fig. High noise receiver and its output

Receiver

External Noise

Amplified Echo Signal

Amplified Internal Noise

External Amplified Noise

Masked Echo Signal

EXTERNAL EMI DUE TO NATURAL

PHENOMENA

• The electromagnetic interference caused

by natural phenomena is seasonal

dependent and effects the radar operation.

• However, the effect is minimum in modern

radars operating between 3 and 30 GHz.

Fig. Effect of clutter

Storm Centre

Plane Echo Obscured

PPI Screen

EMI FROM LAND MASSES

• Land masses screen an echo in the receiverdisplay.

• The reflected signals from land masses areuseful in navigation and mapping radars.

• But in radars used for detection, the reflectedsignals from land masses mask the requiredecho signals.

• A typical situation in which the land massescreate an EMI in the radar display is shown inbelow fig.

Fig. Effect of land masses

Aircraft No. 1

Aircraft No. 2

Aircraft No. 2 Echo

Aircraft No. 1 Echo

EFFECT OF EARTH CURVATURE ON

RADAR OPERATION

• The curvature of earth creates shadow zones.

• It prevents the detection of targets at faraway

distances.

• The radar horizon reduces the maximum range

of the radar.

• A typical situation in which the curvature of the

earth is affecting the radar operation in the

detection of objectives is shown in below fig.

Fig. Effect of Earth’s Curvature

EFFECT OF SIZE, SHAPE OF THE

OBJECT AND MATERIAL

• The radar electromagnetic waves are

reflected from all objects in their path.

• But the strength of the reflected wave

depends on size, shape of the object and

the material with which it is made.

• The reflected wave is strong from metal,

large and close and flat objects.

• Echoes from different objects are shown inbelow fig.

Fig. Echoes from different objects

Metal Object

Large Object

Close Object

Flat Object

Irregular Object

Small Object

Distant Object

Wood Object

Strong Echo

Strong Echo

Strong Echo

Strong Echo

Weak Echo

Weak Echo

Weak Echo

Weak Echo

Receiver

Display

EFFECT OF TRANSMITTER POWER ON

RADAR OPERATION

• The radar with high transmitter power has

long range of detection.

• The low power radar transmitter prevent

the detection of objects.

• A typical situation in which the effect of transmitter power

effects echoes is shown in below figs.

Fig. Effect of high power transmitter

High Power Transmitter

High Resolution

Fig. Effect of low power transmitter

Low Power Transmitter Low

Resolution

EFFECT OF RECEIVER SENSITIVITY

• The sensitivity of the receiver depends on thelevel of noise generated by it.

• The quality of the receiver is usually describedby noise figure.

• Ideally noise figure is unity.

• The noise generated in the receiver is amplifiedand affects the detection of the objects.

• A typical situation in which the effect ofsensitivity on the radar detection is shown inbelow fig.

Fig. Effect of receiver sensitivity

Receiver

External Noise

Amplified Echo Signal

Amplified Internal Noise

External Amplified Noise

Masked Echo Signal

Total Noise

Echo

EFFECT OF BROAD BEAM

• The broad beam makes target

discrimination to be poor.

• A typical situation in which two aircrafts in

a broad beam of the radar antenna create

a single echo pulse in the radar display is

shown in below fig.

Fig. Effect of broad beam : Poor discrimination of targets

Broad Beam

• The improved discrimination of the targetswith a narrow beam is shown in fig.

Fig. Effect of narrow beam : Good discrimination of targets

Narrow Beam

1

2

1 2

EFFECT OF THE FAN BEAMS

• The fan beam form radar antennas are

useful for search the targets with less

number of scans of the beam.

EFFECT OF NARROW

SEARCHLIGHT BEAMS

• The narrow searchlight beam provides

accurate determination of range, bearing

and elevation angles of the targets.

EFFECT OF TIME INTERVAL

BETWEEN PULSES

• The time interval between pulses should

be sufficiently long to receive the echo

signals before the next pulse is

transmitted.

• The short intervals create confusion in the

radar display.

EFFECT OF PULSE DURATION

• Narrow pulse width provides good target discrimination.

• The rage is obtained from CRT by measuring distancebetween the leading edge of the transmitter pulse andleading edge of receiving pulse. (below fig.).

Fig. Range measurement

Range

Transmitted pulse Received pulse

• The effect of transmitted pulse width is shown in below figs.

Fig. Effect of broad pulse Fig. Effect of narrow pulse

The time interval between pulses should be long to

receive all echoes with clarity before the next pulse is

transmitted.

Transmitted pulse

Ambiguous echo

pulse

Transmitted pulse

Unambiguous echo

pulse

SUMMARY OF EFFECT OF DIFFERENT FACTORS ON

RADAR OPERATION

S. No. Parameter Advantage Disadvantage

1. External EMI nil searching and position finding becomes different

2. Internal EMI nil searching and position finding becomes different

3. Land masses the reflected signals from land masses are useful in navigation and mapping radars

detection become different as echo signals from land masses mask the required signals.

4. curvature of earth nil reduce the radar range

5. size of the object beam can be narrow for detection echo becomes weak

6. irregular object nil echo becomes weak

7. metal object echo becomes strong detected by enemy easily

8. Insulator object not detected by enemy echo becomes negligible

9. high transmitted power radar range becomes high not economical

10. low transmitted power radar range becomes small economical

11. low frequency loss of power in atmosphere is small

angle discrimination is poor

12. High frequency angle discrimination is better loss of power in atmosphere is high

13. large pulse width searching is good range discrimination is poor

14. small pulse width range discrimination is good searching is poor

15. high receiver sensitivity easy to detect weak echos nil

16. low receiver sensitivity nil not easy to detect weak echos

17. low PRF nil flow of information is not smooth

18. high PRF flow of information is smooth nil

19. high radar cross-section of the target

easy detection of target helps enemy to detect the targets

20. low radar cross-section enemy cannot detect the target not easy to detect target

S. No. Parameter Advantage Disadvantage

SIGNAL TO NOISE RATIO (SNR)

• The noise is either internal or external.

• It disturbs the ability of the receiver to

detect the required signal.

• The noise is internally generated within the

receiver.

• It also may come from external man-made

and natural sources.

• Ideally, SNR is infinite.

INTERNAL NOISE OR EMI• One such noise is thermal noise. This is also called Johnson noise.

This is generated by the thermal motion of the conducted electrons

in receiver.

The thermal noise depends on

• bandwidth,

• absolute temperature, T

• Boltzman constant, Joules/degree Kelvin.

• In fact, its magnitude of thermal noise power proportional to and

T. That is,

Here, k = Boltzman constant, =

T = temperature,

= receiver bandwidth or noise bandwidth

nB

nB

nn TBp

nn kTBp

K/J1038.1 o23

nB

RADAR CROSS–SECTION OF

TARGETS (RCS),

• The radar cross-section is the targets

relative reflecting/scattering size.

• It represents the magnitude of the echo

signal returned to the radar by the target.

• It is defined as the ratio of power reflected

towards the radar receiver per unit solid

angle to the incident power density per 4.

• That is,

Here, = radar cross-section,

R = the range of the target from the

radar, m

= incident electronic field on the target, V/m

= reflected electronic field strength, V/m

4densitypowerincident

anglesolidunit/receiverradarthetowardsreflectedPower

2

i

2

r2

E

ER4

iE

rE

• From the above definition, the radar cross-

section is obtained by measuring the

received echo amplitude, incident signal

amplitude and the target range.

• It is a part of target radar signature.

• The signature depends on radar cross-

section and the Doppler spectrum of a

target.

RCS has 3 components.

• Area of the target

• The reflectivity of the target

• The antenna-like gain of the target

• The radar cross-section of different targets are shown in the following table

2m

510

410

S. No. Target RCS

1. Bird 0.01

2. Small open boot 0.02

3. Conventional missile 0.5

4. Man or Women 1.0

5. Small single engine aircraft 1.0

6. Small pleasure boat 2.0

7. Bicycle 2.0

8. Small fighter plane 2.0

9. Large fighter aircraft 6.0

10. Cabin Cruisers 10.0

11. Insect 10.5

12. Medium Bomber 20.0

13. Large Bomber 40.0

14. Jumbo Jet 100

15. Automobile 100

16. Pickup Truck 200

17. Small Insect

18. Large Insect

19. Helicopter 3.0