8/3/2019 science 14-12012

1/29

PREFACE

Radar is an exhaustive source of detection and find the location of objects like aircraft,

ships, space crafts, vehicles and the natural environment etc.

Keeping this in mind the present dissertation is based on radar and to study its

structure. The outline of the dissertation is as follows:-

In the chapter firstINTRODUCTION we have discussed about the meaning of radar

and how radar works and general structure of radar.

In the chapter secondFREQUENCIES RANGE USED IN RADAR we discussed in

detail about frequency band which are used in radar system and about pulse

consideration.

In the chapter third OBJECTS OF RADAR we discuss about the various pest of radar

like as radar antenna and radar display and the application of radar system.

At last I hope it will be a successful effort in understood the important of radar system.

8/3/2019 science 14-12012

2/29

CONTENTS

CHAPTER-1

INTRODUCTION OF RADAR

Meaning of radar/definition of radar

History of radar

Block diagram of radar

Basic principle of radar

CHAPTER-2

FREQUENCIES RANGE USED IN RADAR

Radar frequencies

Pulse consideration

Pulse duration

Pulse repetition frequency

Maximum unambiguous range

CHAPTER-3

OBJECTS OF RADAR

Radar antennas and scanning

Radar display

Applications of radar

CHAPTER-4

Conclusion

Refrences

8/3/2019 science 14-12012

3/29

CHAPTER I

INTRODUCTION

1.1 Meaning of RADAR:-

The term radar is the abbreviation for:-

Radar is not a single instrument but an electronic device which includes various

techniques employed for the purpose of detection and location of objects at

distances that for exceed the range of human vision .As the performance of radar

is unaffected by darkness , fog and rain it therefore can be used all weather

conditions to find the positions of mountains , icebergs in sea, share lines lakes

etc.

RADAR is an electromagnetic system which is used for detection and location of

object (target) like aircraft, ships ,space crafts ,vehicles and natural environment.

In others word radar is an object detection system which uses radio waves to

determine the range altitude direction as speed of objects. It can be used to

detect aircraft ,ships ,spacecraft guided missiles, motor vehicles, weather for

motion.

In the transmitted radar signal, the electric field is perpendicular to the direction

of propagation, and this direction of the electric field is the polarization of the

wave. Radars use horizontal, vertical, linear and circular polarization to detect

different types of reflections. For example, circular polarization is used to

minimize the interference caused by rain. Linear polarization returns usually

indicate metal surfaces. Random polarization returns usually indicate a fractal

surface, such as rocks or soil, and are used by navigation radars.

Radar= Radio detection and ranging

8/3/2019 science 14-12012

4/29

The information provided by radar includes the bearing and range (and therefore

position) of the object from the radar scanner. It is thus used in many different

fields where the need for such positioning is crucial. The first use of radar was for

military purposes: to locate air, ground and sea targets. This evolved in the

civilian field into applications for aircraft, ships, and roads.

1.2 History of radar:-

The history of radar starts with experiments by heinrich hertz. He experiments

by radio waves were reflected by metallic objects. It was German engineer

christion hudsmeyer who first used them to build a simple ship detection device

intended to help avoid collision in fog.

The name radar comes from the acronym radar coined in 1940 by the u.s. navy

for public reference to their highly classified work in radio detection and ranging .

Before 1934,no single system gave this performance, some systems were omni-

directional and provided ranging information, while other provided raugh

directional information but not range.

It was enolved deering the years just before world war II. Independently and

more as less simultaneously in Great Britain.

A key development was the use of pulses that were timed to provide ranging

which were sent from large antennas that provided accurate directional

information, combining the two allowed for accurate plotting of target.

1.3 BLOCK DIAGRAM OF PULSED RADAR

8/3/2019 science 14-12012

5/29

1. Transmitter:-

The transmitter may be:-

y Microwave amplifier (klystron TWT)

y Microwave oscillator (magnetron)

Magnetron has been widely used because it provides high average power and its

turned on and off by the pulse modulates for generating repetitive train of pulses.

2. Antenna:-

The electromagnetic wave generate by the transmitter travel through a waveguide to antenna. The electromagnetic wave radiated into free space as pulse of

radio wave. Antenna can be mechanically sterred parabolic reflectors, plannar

array as electronically streered phased array. For both transmitting and

receiving operation a single antenna is generally used as a special

transmit/receive switch or duplexer divice,

8/3/2019 science 14-12012

6/29

3. Duplexer:-

The duplexer is the device which permits a single antenna can be used an a time

shared basis for both transmitting and receving.when the transmitter is in

operating mode, the duplexer produces a short circuit at the input to the receiver

so that transmitting power flows to the antenna not to the receiver. In similar

manner reflected signal is directed to receiver not to the transmitter.

4. Receiver:-

The receiver section of radar is always supesheterodyne type. The input (RF

STAGE) can be low noise transistor amplifies. The mixer and local oscillator

convert the RF signal into an intermediate frequency signal.

In some radar application, the low noise input stage is excluded ,and the mixerreceiver with a mixer as the input stage becomes less sensitive because of the

mixer higher noise fig. A mixer has greator dynamic range. Less vulnearability to

external electromagnetic interference and less susceptibilty to overload.

5. IF AMPLIFIER:-

The intermediate frequency amplifier boost the mixer output at the intermediate

frequency without any distortion in the pulse waveform.The signal band width ofa superheterodyne receiver is defind by the bandwidth of its if stages

The centre frequency of a typical IF amplifier is in the range 30-60 MHz. while the

bandwidth is of the order of 1 MHz.

6. DETECTORS:-

The IF amplifier stage is followed by a second detector, or demodulator.

A diode detector may be used for demodulating as for detection of transmitting

signal. The combination of IF amplifier, demodulator and video amplifier act as

an envelope to pass the pulse modulation and remove the carrier frequency.

7. VIDEO-AMPLIFIER:-

8/3/2019 science 14-12012

7/29

The role of video amplifier in radar receiver is to provide sufficient amplification

or to increase the level of the input signal to a magnitude where it can be seen

easily on cathode ray tube (CRT).

8. DISPLAY:-

The signal from video amplifier is given for thres hold decision, which decides

wheter target is present as not. The decision is based on the magnitude of

reciver output. If the magnitude of received signal is large enough to exceed a

pre-defined theeshold, the decision is that target is present.

If the level of received signal below the predefined threshold only noise is

present. The radar received receivers many echo pulse from a target, the

process of adding these pulse together to obtain a greater SNR,is called

integration. The integration is found is the video portion of the receiver.

Display can be further divided into these types-

A-SCOPE

B-SCOPE

C-SCOPE

PPI

1.4 BASIC PRINCIPAL OF RADAR

8/3/2019 science 14-12012

8/29

-Transmitter generates an electromagnetic signal that is transmitted into free

space by an antenna.

-The transmitted electromagnetic signal strike on target and reradiates from

target in from of echo-signal.

-The echo-signal finally collected by radar receiver

-Radar receiver determine the location and range of target.

-The range of a target is determined by measuring the time it takes for the

transmitted signal to travel to target and return back to radar

If is the time of radar signal to travel to the target and return back then range

of a target

8/3/2019 science 14-12012

9/29

Where c is the velocity of light (3 X108m/s)

The electro-magnetic waves are reflected if. They meet an electrically leading

surface. If these reflected waves are received again at the place of their origin,

them that means an obstacle is in the propagation direction. Electromagnetic

energy travels through air at a constant speed at approximately the speed of light

(3 X108m/s) or 186,000 statute miles per sec. or 162,000.

This constant speed allows the determination of the distance between the

reflecting objects (airplane, ships or cars) and the radar site by measuring the

running time of the transmitted pulses.

This energy normally travels through space in a straight line and will vary only

slightly because of atmospheric and weather conditions. By using of special

radar antennas. This energy can be focused into a desired direction. Thus the

direction (in azimuth and elevation) of the reflecting objects can be measured.

These principles can basically be implemented in a radar system and

allow the determination at the distance, the direction and the height of the

reflecting object.

8/3/2019 science 14-12012

10/29

CHAPTER II

FREQUENCIES RANGE USED IN RADAR

2.1 RADAR FREQUENCIES:-

The spectrum of the electromagnetic waves shows frequencies up to 1024

Hz. This very large complete range is subdivided because of different physical

qualities in different sub range. The division of the frequencies to the different

ranges was compacted on criteria formerly which arose historically and a new

division of the wave bands which is used internationally is out dated and arose so

in the mean time.

Radar system work in a wide band of transmitted frequencies, the higher

frequency of a radar system ,the more it is affected by weather condition such as

rain or clouds. But the higher better is the accuracy of the radar system.

The radar is generally operated in microwave frequency region. The radar

operate in frequencies ranging from about 100MHz to 36 GHz.

8/3/2019 science 14-12012

11/29

BAND

DISIGNATION

NOMINAL FREQUENCY

RANGE

SPECIFIC RADAR BANDS ON

ITU ASSIGNMENT (GHz)

VHF 30-300MHz0.138-0.144GHz

0.216-0.255GHz

UHF 300-1000MHz0.42-0.45GHz

0.85-0.94GHz

L 1-2GHz 1.21-1.40GHz

S 2-4GHz 2.30-2.50GHz

C 4-8GHz 2.30-2.50GHz

X 8-12GHz 8.50-10.68GHz

Ku12-18GHz 13.4-14.0GHz

15.7-17.7GHz

K 18-27GHz 24.05-24.25GHz

Ka 27.40GHz 33.40-36.00GHz

HF and VHF Band:-

8/3/2019 science 14-12012

12/29

These radar bands below 300MHz have a long historically tradition because

these frequencies represented the frontier of radio technology at the time during

the world war-II.

Today these frequencies are used for early warning radars and so called OVER

THE HORIZON (OTH) Radar. Using these lower frequencies, it is easier to

obtain high power transmitters, the attenuation of the electro-magnetic waves is

lower than using higher frequencies. On the other hand, the accuracy is limited

because a lower frequency requires antennas with very large physical size

which determines angle accuracy and angle resolutions.

These frequency band are used by other communications and

broadcasting services too, therefore the bandwidth of the radar is limited (at the

expense of accuracy and resolution again.) these frequency bands are currently

experiencing a comeback, while the actually used stealth technologies dont

have the desired effect at extremely low frequencies.

UHF RADAR:-

There are some specialized radar sets developed far this frequency band

(900MHz to 1GHz). Its a good frequency for the operation of radar for the

detection and tracking of satellites and ballistic missiles over a long range these

radar operate for early warning and target acquisition like the surveillance radar

for the MEDIUM EXTENDED AIR DEFENSE SYSTEM (MEADS).

Some weather radar application e.g. wind profiles work with these frequencies

because the em waves are very low affected by clouds and rain. The new

technology of ULTRA WIDE BAND (UWB). Radar uses all frequencies from A

to C-band, UWB-radar transmit very low pulses in all frequencies simultaneously.

They are used for technically material examination and as GROUND

PENETRATING RADAR(GPR) for archaeological explorations.

L-BAND RADAR:-

8/3/2019 science 14-12012

13/29

This frequency band (1-2 GHz) is preferred for the operation of long range air

surveillance radar out to 850 NM (=400km). They transmit pulses with high

power, broad band width and an intra pulse modulation often due to the

curvature of the earth the achievable maximum range is limited for targets flying

with low altitude .These objects disappear very fast behind the radar horizon.

In air-traffic management (ATM) long range surveillance radar like the air

route surveillance radar (ARSR) works in this frequency band coupled with a

mono-pulse secondary surveillance radar (MSSR).They use a relatively large but

slower rotating antenna.

L-band is good as monomonic rhyme as large antenna as long range.

S-BAND RADAR:-

The atmospheric attenuation is higher then in d-band. Radar sets need a

considerably higher transmitting power than in a lower frequency range to

achieve a good maximum range. As example given the medium power radar

(MPR) with a pulse power of up to 20 MW.

In this frequency range the influence of weather conditions is higher than in d-

band. Therefore a couple of weather radar work in s-band radar but more in sub

tropic and tropic climate conditions. Because here the radar can see beyond a

severe storm. Special airport surveillance radars (ASR) are used at airports to

detect and display the position of aircraft in the terminal area with a medium

range up to 50-60NM (=100km). An ASR detects aircrafts position and weather

conditions in the vicinity of civilian and military airfields .The designators s-band

(contrary to L-band) is good as mnemonic rhyme as smalls antenna or shorter

range.

C-BAND:-

8/3/2019 science 14-12012

14/29

In C-band radar there are many mobile military battle field surveillance radar sets

with short as medium range. The size of the antenna provides an excellent

accuracy. And resolution but the relatively small sized antenna doesnt bother a

fast relocation. The influence of bad weather conditions is very high. Therefore

air-surveillance radars use an antenna feed with circular polarization often. This

frequency band is predetermined for most types of weather radar used to locate

precipitation in temperate zone like Europe.

X AND Ku-BAND RADAR):-

In this frequency band (8 to 12 GHz) the relationship between used wave length

and size of the antenna is considerably better than in lower frequency bands.

These band is a relatively popular radar band for military applications like

airborne radars and performing the roles of interceptor, fighters and of ground

target. A very small antenna size provides a good performance. Missile guidance

systems at band are of a convenient size and are therefore of interest for

applicable where mobility and light weight are important and very long range is

not a major requirement.

This frequency band is wide used maritime civil and military and cheap antenna

with a high resolution speed are adequate for a fair maximum range and a good

accuracy slotted wave guide and small patch antenna are used as radar

antenna. Under a protective random mostly.

This frequency band is also popular for space borne or airborne imaging

radars based or synthetic aperture radars (SAR) both for military electronic

intelligence and civil geographic mapping. A special inverse synthetic aperture

radar (ISAR) is in use as a maritime airborne instrument of pollution control.

K-AND Ka BAND RADAR:-

8/3/2019 science 14-12012

15/29

The higher the frequency, the higher is the atmospheric absorption and

attenuation of the waves. Other wise the achievable accuracy and the range

resolution rise too..Radar applications in this frequency band provide short range

very high resolution and high data renewing rate. In ATM these radar sets are

called surface movement radars(SMR).

V-BAND RADAR:-

By the molecular dispersion (here this is the influence of the air humidity)

This frequency band stay for a high attenuation. Radar applications are limited

for a short range of a couple of meters here.

W-BAND RADAR:-

There are two phenomena visible a maximum of attenuation at about 15 GHz

and a relative minimum at about 96GHz.

OPERATING CHARACTERISITCS OF A RADAR

FREQUENCY/PULSE CONSIDERATIONS.

The performance of a radar system depends upon the factors such as the

desired data and nature of the targets: and these factors on the others band,

depend upon the choice of operating frequency. Pulse duration and repetition

rate, the power out-put of the transmitter, choice of indicator type sensitivity and

band-width of the receiver and radiation pattern of antenna.

CHOICE OF OPERATING FREQUENCY:-

Most pulse radar system operates all frequencies from above 1000mc/s to about

70,000mc/s. The use of such high frequencies has the advantages that:-

8/3/2019 science 14-12012

16/29

At such high frequencies a sharp and well confined radiation beam can be

achieved with an antenna structure of relatively small physical size.

Higher the frequency, shorter may be the transmitted pulses which provide

good range resolution.

The use of high frequencies also suffers with the following main disadvantages

Noise figure increases more with frequency

Power generated in the transmitter tends to the less as the frequency is

increased.

Radar pulses should have vertical sides and flat tops. The leading edge of

the transmitted pulse must be vertical to ensure that the leading edge of the

received pulse (echo) is also close to the vertical otherwise uncertainty will

prevail as to at what precise instant echo has been received.

Further pulse trailing edge should also be vertical (steep) otherwise (if not

steep) It will have the effect of lengthening the period of time for which the

receiver is disconnected from the antenna therefore it limit the minimum range of

the radar.

PULSE DURATION:-

For good resolving capabilities, short duration pulses in the form a narrow

radiating beam should be employed. For a good range resolution, pulse duration

of 1 sec or less are employee pulse width used in radar range from about 0.2

sec. long to values of the order of 30 sec.

PULSE REPETITION FREQUENCY:-

The pulse repetition frequency is made sufficiently small so that the time spent is

the path between radar and distant target may not exceed the interval between

transmitted pulses repetition frequencies used in radar work usually vary for 350

to about 10,000 cycles, short range radar use high pulse repetition rates.

8/3/2019 science 14-12012

17/29

TRANSMITTER POWER OUTPUT:-

To detect target at range up to several hundred miles transmitter peak power

output of more than are megawatt may be required. For a particular radar

transmitter power is determined by the maximum distances over which it is

desired to receiver target information.

A typical radar used for the detection of conventional aircraft at range of

100 or 200 miles might employ a peak power of the order of lMW, a pulse width

of several microseconds and a pulse repetition frequency of several hundred

pulse per second.

MAXIMUM RANGE:-

It depends upon the energy content of the transmitted pulses and the sensitivity

of receiver. For better sensitivity random noise generated in the input section of

the receiver should be minimized.

MAXIMUM UNAMBIGUOUS RANGE(Rumb):-

The signal is radiated into space by a radar in the form of pulse modulated

sine wave. Once a transmitted pulse radiated by the radar, sufficient length of

time must be allowed so that all echo signal due to this pulse may be return to

the radar before next pulse is transmitted. Therefore the rate by which the pulse

may be transmitted is define by the longest range at which the target areexpected.

It pulse repetition time Tp is too short echo signal from target and

ambiguities in the measuring might result. It clearly indicates, if Tp is too short an

echo signal from a long distance target might arrive after the transmission of next

8/3/2019 science 14-12012

18/29

pulse. Echoes that arrive after the transmission of next pulses are called second

time around echoes(multiple time around echoes)

The maximum unambiguous range is defined by range beyond which

target appear as second time around echoes

The Rumb is given by

C=velocity of light =3X108 m/s

TP=pulse repetition period

The Rumb can be defined in terms of pulse repetition frequency.

=

CHAPTER III

OBJECTS OF RADAR

ANTENNAS AND SCANNING

The majority of radar antennas use dipole or horn-fed paraboloid reflectors, or at

least reflectors of a basically parabolid shape. In each of the latter the beamwidth

in the vertical direction (the angular resolution) will be much worse than in the

horizontal direction, but this is immaterial in ground-to-ground or even radars. It

has the advantages of allowing a significantly reduced antenna size and weight

reduced wind loading and smaller drive motors.

Antenna scanning radar are often made to scan a given area of the surrounding

space, but the actual scanning pattern depends on the application .

8/3/2019 science 14-12012

19/29

The first of these is the simplest but has the disadvantage of scanning in the

horizontal plane only. There are many applications for this type of scan in

Searching the horizon, e.g.-in ship to ship radar, the nodding scan is an

extension of this; the antenna is now rocked rapidly in elevation while it rotates

more slowly in azimuth, and scanning in both planes is obtained. The system can

be used to scan a limited sector or else it can be extended to cover the complete

hemisphere. Another system capable of search over the complete hemisphere is

the helical scanning system, in which the elevation of the antenna is raised

slowly while it rotates more rapidly in azimuth. The antenna is returned to its

starting point at the completion of the scanning cycle and typical speeds are a

rotation of 6 rpm accompanied by a rise rate of 20degree/minute.

Antenna tracking

Having acquired a target through a scanning method as just described ,it may

then be necessary to locate it very accurately, perhaps in order to bring weapons

8/3/2019 science 14-12012

20/29

to bear upon it. Having an antenna with a narrow, pencil-shaped beam helps in

this regard, but the accuracy of even this type of antenna is generally insufficient

in itself.

The direction of the antenna beam is rapidly switched between two positions in

this system, as shown so that the strength of the echo from the target will

fluctuate at the switching rate, unless the target is exactly midway between the

two directions .in this case the echo strength will be same for both antenna

positions, and the target will have been tracked with much greater accuracy than

would be achieved by merely pointing the antenna at it.

Conical scanning is a logical extension of lobe switching. it is achieved by

mounting the parabolic antenna slightly off centre and then rotating it about the

axis of the parabola, the rotation is slow compared to the PRF.

The conical scan is derived from the surface described in space by the pencil

radiation pattern of the antenna , as the tip of the pattern moves in a circle. The

same argument applies with regard to target positioning as for sequential lobing,

except that the conical scanning system is just as accurate in elevation as in

azimuth, whereas sequential lobing is accurate in one plane only.

8/3/2019 science 14-12012

21/29

There are two disadvantages of the use of either sequential lobing or conical

scanning. The first and most obvious is that the motion of the antenna is now

more complex, and additional servomechanisms are required. The second

drawback is due to the fact that more than one returned pulse is required to

locate a target accurately (a minimum of four are required with conical scan, one

for each extreme displacement of the antenna). The difficulty here is that target

cross section is changing, because of its change in attitude or for other reasons,

the echo power will be changing also. Hence the effect of conical scanning(or

sequential lobing,for that matter)will be largely nullified. From this point of view,

the ideal system would be one in which all the information obtained by conical

scanning could be achieved with just one pulse. Such a system fortunately exists

and is called monopulse.

Each of the four feeds produces a slightly different beam from the one reflector,

so that in transmission for individual beams stabout into space, being centered

on the direction a beam would have had from a single feed placed at the focus of

the reflector .as in conical scanning and sequential lobing, no differences will be

recorded if the target is precisely in the axial direction of the antenna. However

once the target has been acquired, any deviation from the central position. Will

be shown by the presence of a vertical difference signal, a horizontal difference

signal, or both. The receiver has three separate input channels (one for each of

the three signals)consisting of three mixers with a common local oscillator, three

IF amplifiers and three detectors. the output of the sum channel is used to

provide the data generally obtained from a radar receiver, while each of the

difference or error signals feeds a servoamplifier and motor, driving the antenna

so as to keep it pointed exactly at the target. Once this has been done ,the output

of the sum channel can be used for the automatic control of gunnery if that is

the function of the radar.

The advantage of monopulse, as previously is that it obtains with one pulse the

information which required several pulses in conical scanning. monopulse is not

subject to errors due to the variation in target cross section. It requires two extra

8/3/2019 science 14-12012

22/29

receiving channels and a more complex duplexer and feeding arrangement and

will be bulkier and more expensive.

RADAR DISPLAY

The main purpose of radar receiver is to present the output so that an operator

can easily and accurately determine the presence of target instead of displaying

only detection many surveillance radar display target track vectoralong with

auxiliary alphanumeric information to an operator.

If display is connected directly with the output of radar receiver without any

processing the output is defined as raw video. If receiver output is processed by

an detector before displaying it is defined called as synthetic video.

1. A SCOPE DISPLAY

A-scope display is the most popular type of system for displaying modulation. it is

also indicate the range of the target in a scope display vertical deflection is

directly proportional to the amplitude of the receiver output and the horizontal

deflection is proportional to range of target .this display is suitable for manual

tracking radar.

In operation of a scope display, a available to scan the CRT screen

horizontally by applying a linear saw tooth voltage to the horizontal deflection

plate in synchronism with transmitted pulses. If demodulated echo signal from

receiver is applied to the vertical deflection plate, it cause vertical deflection from

horizontal line.

8/3/2019 science 14-12012

23/29

2. B-scope display,

Display received signal amplitude as a function of azimuth. This intensity

modulated display has azimuth angle along the horizontal axis and range along

the vertical axis B-scope display is widely used in airbone military radar where

the range and angle to the target are more important than concern about

distortion in the angle dimension

8/3/2019 science 14-12012

24/29

3. C-SCOPE DISPLAY

It is a two angle intensity modulated rectangular display in which azimuth angle

indicated by the horizontal coordinate and elevation angle is determine by the

vertical coordinate.

4. PLAN POSITION INDICATOR(PPI)

The PPI display is an intensity modulation type display, which indicate both range

and azimuth angle of the target in polar coordinate system.

The echo signal received from receiver is firstly demodulated and than applied to

the grid of the CRT tube which is biased slightly beyond cutoff. A beam is made

to deflect radiately outward from centre and also continuousaly around the tube

at the same angular velocity as that of the antenna. The brightness spot on the

screen indicates the presence of target. The distance of the bright spot radiating

outward from the centre determine the distance of the target from radartransmitter. The resolution of screen depends on the bandwidth of the antenna,

pulse width and transmitter frequency.

8/3/2019 science 14-12012

25/29

APPLICATIONS OF RADAR

The radar play important role for purpose although it has been employed in civilian

application.

MILITARY APPLICATIONS

Detection and ranging of enemy target at night

In air defense system operation of offensive missiles and other weapons.

Early warning regarding approaching aircrart or ships.

AIR TRAFFIC CONTROL (ATC)

The radar have been employed throughout the world for safely of aircraft and controlling

air traffic. It is also used for guiding aircraft to a safe landing during disturbed weather.

REMOTE SENSING

Weather observation

Planetary observation

Short range below ground probing.

Mapping of sea ice to route shipping

OTHER APPLICATIONS

8/3/2019 science 14-12012

26/29

The radar speed meter is used widely by police for enforcing speed limit.

In ship safety radar is employed to avoid collision when visibility is poor.

The radar are used to indicate region of precipitation height of an aircraft above

the terrain to avoid hazards related with them.

The space vehicles have used radar for rendezvous and docking for landing on

the moon.

CHAPTER -IV

CONCLUSION

Radar is an electromagnetic system which is used for detection and location of objects

(targets) like aircraft ships space crafts vehicles and natural environment etc.

In operation of radar radio wave are transmitted into space and wave strike on target,

signal reflected from target or object is called as echo signal. Signal reflected by target

is received by radar receiver. The echo signal that is returned to the radar not only

indicates the presence of objects, but gives other target related information.

The radar can operate in darkness, fog, rain and show. In typical climate

condition radar can measure distance with high accuracy.

The different parts of radar structure are:-

8/3/2019 science 14-12012

27/29

a) Transmitter

b) Antenna

c) Duplexer

d) Receiver

e) If amplifier

f) Detector

g) Video amplifier

h) Display

The radar is generally operated in microwave frequency region. The radar operates at

frequencies ranging from about 100MHz to 36 GHz

The electromagnetic wave generated by the transmitter travel through a transmission

line or a wave guide to antenna. The electromagnetic wave radiated into free space as

pulse of radio wave. Antenna can be mechanically steered parabolic reflectors, plannar

array or electronically streered phased array The measure of sharpness and directivity

of the radiated beam from the antenna is, however dependent on its requirements

scanning methods from antenna are:-

a) Horizontal scanb) Nodding scan

c) Helical scan

d) Spiral scan

The signal from video amplifier is given for threshold decision, which decides whether

target is present or not. Display can be further divided into three type

a) A-scope

b) B-scope

c) C-scope

d) PPI

The radar play important role for military purpose, Air traffic control, remote sensing.

8/3/2019 science 14-12012

28/29

REFRENCES

i. Introduction of radar system;Mc Graw Hill

ii. Radar principles ; Nadav levanon

iii. Fundamentals of radar signal processing ;Mark A. Richards

iv. Understanding radar system; Simon philip kingsley

v. Radar handbook; Merrill I skolnik

vi. The discovery of radio waves ;Heinrich Rudolf

vii. Understanding radar ;Harry cale

viii. www.techradar.com

ix. www.radartutorial.eu

8/3/2019 science 14-12012

29/29

x. www.wikipedio.org

xi. www.radar.htm

xii. www.radar.org.ue

xiii. Radar.oreilly.com