Training report on

Industrial training at

On the topic:-

STUDY OF RADAR SYSTEM

Submitted to:-

Submitted by:-

Atul Sharma, B.Tech IV year, ECE

Maharaja Agrasen Institute Of Technology,

GGSIPU

Under:- Mr. Aman Vohra

Start Date for Internship:-June 16th 2014

End Date for Internship:-July 26th 2014

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Preface

This report documents the work done during the summer training at Bharat Electronics limited, Ghaziabad, Uttar Pradesh under the guidance of Mr. Aman Vohra . The report first shall give the overview of tasks performed during the period of training .The technical details about the RADAR and its various applications and the conclusion drawn out of it.

Report shall also elaborate about the future scope of the Radar Technology.

I have tried my best to keep the report simple yet technically correct. I hope I succeed in my attempt.

Atul Sharma

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Acknowledgement

On the very outset of this report, I would like to extend my sincere & heartfelt obligation towards all the personages who have helped me in this endeavour. Without their active guidance, help, cooperation & encouragement, I would not have made headway in the project.

First and foremost, I would like to express my sincere gratitude to my project guide, Mr. Aman Vohra.I was privileged to experience a sustained enthusiastic and involved interest from his side. This fuelled my enthusiasm even further and encouraged me to boldly step into what was a totally dark and unexplored expanse before me.

I would also like to thank Mr. Mohit Saxena who, instead of his busy schedule, always guided me in right direction.

I extend my gratitude to Maharaja Agrasen Institute Of Technology for giving me this opportunity.

Thank You

Atul Sharma

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Table of Content

Introduction........................................................................................06

Historical Overview............................................................................07

Radar Basic Principles........................................................................09

Distance-determination............................................................10

Direction-determination...........................................................11

Maximum Unambiguous Range..............................................13

Minimal Measuring Range......................................................14

Radar Frequency Bands.....................................................................15

Waves and Frequency Ranges.................................................15

Free space Radar equations................................................................17

Radar Coverage..................................................................................19

Cone of Silence........................................................................19

Low-altitude Coverage.............................................................20

Classification of Radar systems.........................................................21

Classification Depending Upon Technology..........................23

Primary Radar..............................................................23 Secondary Radar..........................................................23 Continuous Wave Radar..............................................24 Pulse Radar..................................................................26

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Classification on the basis of design........................................27

Air-defence Radars.....................................................27

Air traffic control (ATC)............................................28

Some Radar Sets................................................................................29

3-D Surveillance Radar (ROHINI).........................................29 Low Level Light-Weight Radar (ASHLESHA).....................30 Low Level Light-Weight Radar (BHARANI)........................31 Indra II....................................................................................32 3-D Tactical Control Radar....................................................33 Tactical Control Radar...........................................................34

Radar Devices...................................................................................35

Radar Antenna........................................................................35

Parabolic Antenna.....................................................35 Cassegrain Antenna...................................................36 Slot Antenna..............................................................36

Radar Transmitter...................................................................37

Radar Receiver........................................................................37

Radar Display..........................................................................37

Radar A- Scope...........................................................38 Radar B-Scopes...........................................................39 Plan-Position Indicator................................................40

Future Research..................................................................................41

Conclusion.........................................................................................42

Bibliography......................................................................................43

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INTRODUCTION

RADAR is acronym for Radio Detection and Ranging. Today, the technology is so common that the word has become Standard English noun. The development of RADAR accelerated and spread in middle and late 1930s with first successful demonstration in 1936. It uses electromagnetic waves in microwave region to detect location, height, intensity and movements of targets. It operates by radiating energy into space and detecting the echo signals reflected from an object, or target. The reflected energy that is reflected to radar not only indicates the presence of target, but by comparing the received echo signals with the signals that were transmitted its location can be determined along with the other target related information. Radar is an active device. It utilizes its own radio energy to detect and track the target. It does not depend on energy radiated by the target itself. The ability to detect a target at great distances and to locate its position with high accuracy are two of the chief attributes of radar. Earlier radar development was driven by military necessities. But, radar now it enjoys wide range of application. One of the most common is the police traffic radar used for enforcing speed limits. Another is weather radar. Other most famous application is air traffic control system.

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HISTORICAL OVERVIEW

Neither a single nation nor a single person is able to say, that he (or it) is the inventor of the radar method. One must look at the “Radar” than an accumulation of many developments and improvements earlier, which scientists of several nations parallel made share. There are nevertheless some milestones with the discovery of important basic knowledge and important inventions:

1865

The World War II RADAR, ’Wurzberg Rise’

The English physicist James Clerk Maxwell developed his electro-magnetic light theory (Description of the electro-magnetic waves and her propagation)

1886 The German physicist Heinrich Rudolf Hertz discovers the electro-magnetic waves and proves the theory of Maxwell with that.

1904 The German high frequency engineer Christian Hülsmeyer invents the “Telemobiloskop” to the traffic supervision on the water. He measures the running time of electro-magnetic waves to a metal object (ship) and back. A calculation of the distance is thus possible. This is the first practical radar test. Hülsmeyer registers his invention to the patent in Germany and in the United Kingdom.

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1917 The French engineer Lucien Lévy invents the super-heterodyne receiver. He uses as first the denomination “Intermediate Frequency”, and alludes the possibility of double heterodyning.

1921 The invention of the Magnetron as an efficient transmitting tube by the US-American physicist Albert Wallace Hull

1922 The American electrical engineers Albert H. Taylor and Leo C. Young of the Naval Research Laboratory (USA) locate a wooden ship for the first time.

1930 Lawrence A. Hyland (also of the Naval Research Laboratory), locates an aircraft for the first time.

1931 A ship is equipped with radar. As antennae are used parabolic dishes with horn radiators.

1936 The development of the Klystron by the technicians George F. Metcalf and William C. Hahn, both from General Electric. This will be an important component in radar units as an amplifier or an oscillator tube.

1940 Different radar equipments are developed in the USA, Russia, Germany, France and Japan.

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RADAR BASIC PRINCIPLE

The electronic principle on which radar operates is very similar to the principle of sound-wave reflection. If you shout in the direction of a sound-reflecting object (like a rocky canyon or cave), you will hear an echo. If you know the speed of sound in air, you can then estimate the distance and general direction of the object. The time required for an echo to return can be roughly converted to distance if the speed of sound is known. RADAR PRINCIPAL

Radar uses electromagnetic energy pulses. The radio-frequency (RF) energy is transmitted to and reflected from the reflecting object. A small portion of the reflected energy returns to the radar set. This returned energy is called an ECHO, just as it is in sound terminology. Radar sets use the echo to determine the direction and distance of the reflecting object. The word radar is a contraction of

RAdio Detecting And Ranging

As implied by this contraction, radars are used to detect the presence of an aim (as object of detection) and to determine its location. The contraction implies that the quantity measured is range. While this is correct, modern radars are also used to measure range and angle. The following figure shows the operating principle of primary radar. The radar antenna illuminates the target with a microwave signal, which is then reflected and picked up by a receiving device. The electrical signal picked up by the receiving antenna is called echo or return. The radar signal is generated by a powerful transmitter and received by a highly sensitive receiver.

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Distance-determination

The radar transmits a short radio pulse with very high pulse power. This pulse is focused in one direction only by the directivity of the antenna, and propagates in this given direction with the speed of light.

If in this direction is an obstacle, for example an airplane, Runtime measurement by radar

part of the energy of the pulse is scattered in all directions. A very small portion is also reflected back to the radar. The radar antenna receives this energy and the radar evaluates the contained information.

The distance we can measure with a simple oscilloscope. On the oscilloscope moves synchronously with the transmitted pulse a luminous point and leaves a trail. The deflection starts with the transmitter pulse. The luminescent spot moves to scale on the oscilloscope with the radio wave. At this moment, in which the antenna receives the echo pulse, this pulse is also shown on the oscilloscope. The distance between the two shown pulses on the oscilloscope is a measure of the distance of the aircraft.

Since the propagation of radio waves happens at constant speed (the speed of light c0) this distance is determined from the runtime of the high-frequency transmitted signal. The actual range of a target from the radar is known as slant range. Slant range is the line of sight distance between the radar and the object illuminated. While ground range is the horizontal distance between the emitter and its target and its calculation requires knowledge of the target's elevation. Since the waves travel to a target and back, the round trip time is dividing by two in order to obtain the time the wave took to reach the target. Therefore the following formula arises for the slant range:

R = c0· t where: c0 = speed of light = 3·108 m/s

t = measured running time [s]R = slant range antenna

2

The distances are expressed in kilometre or nautical miles (1 NM = 1.852 km).

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Derivation of the equation

Range is the distance from the radar site to the target measured along the line of sight.

v = S

t

c0 = 2·R

t

The factor of two in the equation comes from the observation that the radar pulse must travel to the target and back before detection, or twice the range.

R = c0·t

in meters 2

Where c0= 3·108 m/s, is the speed of light at which all electromagnetic waves propagate.

If the respective running time t is known, then the distance R between a target and the radar set can be calculated by using this equation.

Direction-determination

The angular determination of the target is determined by the directivity of the antenna. Directivity, sometimes known as the directive gain, is the ability of the antenna to concentrate the transmitted energy in a particular direction. An antenna with high directivity is also called a directive antenna. By measuring the direction in which the antenna is pointing when the echo is received, both the azimuth and elevation angles from the radar to the object or target can be determined. Direction-determination (bearing)

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The accuracy of angular measurement is determined by the directivity, which is a function of the size of the antenna.

Radar units usually work with very high frequencies. Reasons for this are:

Quasi-optically propagation of these waves. High resolution (the smaller the wavelength, the smaller the objects the

radar is able to detect). Higher the frequency, smaller the antenna size at the same gain.

The True Bearing (referenced to true north) of a radar target is the angle between true north and a line pointed directly at the target. This angle is measured in the horizontal plane and in a clockwise direction from true north.

Variation of echo signal strength

The antennas of most radar systems are designed to radiate energy in a one-directional lobe or beam that can be moved in bearing simply by moving the antenna. As you can see, the shape of the beam is such that the echo signal strength varies in amplitude as the antenna beam moves across the target. In actual practice, search radar antennas move continuously; the point of maximum echo, determined by the detection circuitry or visually by the operator, is when the beam points direct at the target. Weapons-control and guidance radar systems are positioned to the point of maximum signal return and maintained at that position either manually or by automatic tracking circuits.

In order to have an exact determination of the bearing angle, a survey of the north direction is necessary. Therefore, older radar sets must expensively be surveyed either with a compass or with help of known trigonometrically points. More modern radar sets take on this task and with help of the GPS satellites determine the north direction independently.

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Maximum Unambiguous Range

Second-sweep echo in a distance of 400 km

It becomes obvious that we cannot send out another pulse until a time window has passed, in which we expect to see a return echo. The maximum measuring distance Rmax of a radar unit isn't orientated only at the value determined in the radar equation but also on the duration of the receiving time.

The radar timing system must be reset to zero each time a pulse is radiated. This is to ensure that the range detected is measured from time zero each time. Echo signals arriving after the reception time are placed either into the

Following transmit time where they remain unconsidered since the radar equipment isn't ready to receive during this time, or

Into the following reception time where they lead to measuring failures (ambiguous returns).

The maximum range at which a target can be located so as to guarantee that the leading edge of the received backscatter from that target is received before transmission begins for the next pulse. This range is called maximum unambiguous range or the first range ambiguity. The pulse-repetition frequency (PRF) determines this maximum unambiguous range of given radar before ambiguities start to occur. This range can be determined by using the following equations:

Rmax =

c0 · ( PRT - PW )

2

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Where c0 is the speed of light with 3·108 m/s. The pulse width (PW) in these equations indicates that the complete echo impulse must be received. The pulse repetition time (PRT) of the radar is important when determining the maximum range because target return-times that exceed the PRT of the radar system appear at incorrect locations (ranges) on the radar screen. Returns that appear at these incorrect ranges are referred as ambiguous returns or second-sweep echoes.

Minimal Measuring Range

The Radars “blind range”

Monostatic pulse radar sets use the same antenna for transmitting and receiving. During the transmitting time the radar cannot receive: the radar receiver is switched off using an electronic switch, called duplexer. The minimal measuring range Rmin (“blind range”) is the minimum distance which the target must have to be detected. Therein, it is necessary that the transmitting pulse leaves the antenna completely and the radar unit must switch on the receiver. The transmitting time τ and the recovery time trecovery should are as short as possible, if targets shall be detected in the local area.

Rmin = c0·(τ + trecovery)

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2

RADAR FREQUENCY BANDS

Waves and Frequency Ranges

The spectrum of the electric magnetic waves shows frequencies up to 1024 Hz.

This very large complete range is subdivided because of different physical

qualities in different subranges.

The division of the frequencies to the different ranges was competed on criteria

formerly, which arose historically and a new division of the wavebands which is

used internationally is out-dated and arose so in the meantime. The traditional

waveband name is partly still used in the literature,

Spectrum of EM waves

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Since without that the correct frequency is known, a transformation isn't always

possible into the new wavebands. Often in the manufacturers documents are

published the traditional wavebands. Some radars and its frequency band Radar

systems work in a wide band of transmitted frequencies. The higher the

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

as rain or clouds. But the higher the transmitted frequency, the better is the

accuracy of the radar system.

The figure shows, how the frequency bands are used .

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some radars and its frequency band

FREE RADAR SPACE EQUATION

The radar range equation relates the range of radar to the characteristics of the transmitter, receiver, antenna, target and the medium. Free space actually means that there are no obstacles between radar antenna and the target. Also the free space medium is transparent and homogenous with respect to the refractive index at radar frequency. If the power of a radar transmitter is denoted by Pt and if an isotropic antenna (one which radiates uniformly in all the directions) then the power density at a distance R from the radar is equal to the transmitted power divided by the surface area of sphere of radius R i.e. power density at a distance R from the isotropic source,

= Pt / 4ПR2 watts/m2

Radar usually employs directive antennas to direct the transmitted power Pt into one particular direction. The gain G of an antenna is a measure of the increased power radiated in the direction of the target as compared with the power that would have been radiated from an isotropic antenna. Power density at a distance R from directive antenna of power gain

= Pt.G / 4ПR2 watts/m2

The target intercepts the portion of transmitted power and radiates it in various directions. A measure of the incident power intercepted by the target and reradiated back in the direction of radar is denoted as the radar cross-section of the target (б).The total power intercepted by a target having an area ‘б’ is,

= (Pt .G / 4П R2).б watts

Where б is also defined as the area of the target as seen by the radar. It has units of area in m2. б is a characteristic of a particular target and is a measure of its size and shape. The power density of echo signal at the radar station is

= (Pt .G.б / 4ПR2) . (1/4ПR2) = Pt .G.б/ (4ПR2)2 watts

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The radar antenna captures the portion of the echo power, if the effective area of the receiving antenna is denoted by Ae, the power Pr received by the radar is given by,

Pr = Pt .G.б.Ae / (4ПR2)2 watts

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Maximum radar range is the distance beyond which the target cannot be detected. It occurs when the received echo signal power Pr, just equals the minimum detectable signal (Smin). When Pr = Smin, R = Rmax

We get,

Smin = Pt .G.б.Ae / (4П)2 R4max

Rmax = [Pt .G.б.Ae /(4П)2Smin]1/4

From the antenna theory, we know that G = 4ПAe / λ2

Where λ= wavelength of the radiated energy, Ae = effective area of receiving antenna, G = transmitter gain

Since radar generally use the same antenna for both transmitter and receiver, the above expression for G can be substituted in Rmax relation. Then,

Rmax = [Pt .G.б.Ae / (4П)2Smin]1/4

Rmax = [Pt .Ae2.б / 4П.λ2Smin]1/4

Also, Ae = G.λ2 / 4П,

Rmax = [Pt(Gλ2/4П)2б / 4Пλ2Smin]1/4

Rmax = [Pt .G.λ2 .б / (4П)2 Smin]1/4

These are the two alternate form of maximum radar range equation.

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RADAR COVERAGE

The radar coverage describes area controlled by radar or radar network airspace. In a two-dimensional radar is often used an antenna with a cosecant square pattern. Its main beam direction forms a vertical rectangle with rounded corners, which rotates about a vertical axis. Thus arises on the radar site a room with the geometry of a flat cylinder within which the radar can locate an aerial target. At an Air Surveillance Radar (ASR) (or referred to Terminal Area Radar), this cylinder has a diameter of about 120 NM (220 km) and a height of about 10,000 feet (or 3,000 m)

Cone of Silence

Radar is not designed to detect aircraft directly above the radar antenna. This gap is known as the cone of silence. This gap or cone of silence is the inverted cone mapped out by the rotating antenna as a result of the antenna back angle being less than 90 degrees. Hence, the back angle is an important antenna parameter. If the back angle is shallow then aircraft will fall outside radar cover as they over-fly the radar site. By most radars the actual radius of the cone of silence is the double of the targets height. This means, a target in a height of 10,000 feet (or 3,000 m) enters the cone of silence in a range of 3¼

Radar coverage, located in middle of cone of silence

NM (6,000 m). Aircraft flying in a radar's cone of silence may, however, be detected by another, or several other radar sites a hundred or so miles away due to their overlapping coverage.

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Low-altitude Coverage

The flat cylinder has a relatively smooth lower surface in flat terrain. A curvature of the outer edges upwards is in the order of half a degree. The low-altitude coverage is limited by the shadow formed by the earth's curvature. Uneven terrain such as hills or even mountains and valleys by shading also has an impact on the size of the dead zone. Also this dead zone can be covered by another radar. Despite a large number of organized in a radar network radar, a space will always remain in extremely low altitude at which an

Vertical overlap of the radar coverage areas, above: a typical case of air defence, below a typical case of air traffic control

aircraft can fly below the radar. In practice, however, this is for the pilot not as easy as it must know exactly where to fly for to remain as far away from each radar. In order to keep this lower limit as low as possible, but a very dense network of radars must already be deployed. As you can imagine, countries in mountainous regions have problems to establish a complete area with full radar coverage. For the requirements of national defence, a number of smaller mobile radar sets (as so-called Gap-filler) are established exactly in such gaps when needed. Depending on the task, such overlap is done according to different principles. For the air surveillance on behalf of the national defence a complete radar coverage must be organized down to a height, for example, of 100 m. In crisis or defence case that needs to be lowered even further. However, an overlap to the cones of silence is not necessary.

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CLASSIFICATION OF RADAR SYSTEMS

Depending on the desired information, radar sets must have different qualities and technologies. One reason for these different qualities and techniques

radar sets are classified in

Classification of radar sets

Imaging Radar / Non-Imaging Radar

An Imaging Radar forms a picture of the observed object or area. Imaging radars have been used to map the Earth, other planets, asteroids, other celestial objects and to categorize targets for military systems.

Typically implementations of a Non-Imaging Radar system are speed gauges and radar altimeters. These are also called scatterometers since they measure the scattering properties of the object or region being observed. Non-Imaging Secondary Radar applications are immobilizer systems in some recent private cars.

Primary Radar

A Primary Radar transmits high-frequency signals which are reflected at targets. The arisen echoes are received and evaluated. This means, unlike secondary radar sets a primary radar set receive its own emitted signals as an echo again.

Secondary Radar

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At these radar sets the airplane must have a transponder (transmitting responder) on board and this transponder responds to interrogation by transmitting a coded reply signal. This response can contain much more information, than a primary radar set is able to acquire (E.g. an altitude, an identification code or also any technical problems on board such as a radio contact loss).

Pulsed Radars

Pulse radar sets transmit a high-frequency impulse signal of high power. After this impulse signal, a longer break follows in which the echoes can be received, before a new transmitted signal is sent out. Direction, distance and sometimes if necessary the height or altitude of the target can be determined from the measured antenna position and propagation time of the pulse-signal.

Continuous- Wave Radar

CW radar sets transmit a high-frequency signal continuously. The echo signal is received and processed. The receiver need not to be mounted at the same place as the transmitter. Every firm civil radio transmitter can work as a radar transmitter at the same time, if a remote receiver compares the propagation times of the direct signal with the reflected one. Tests are known that the correct location of an airplane can be calculated from the evaluation of the signals by three different television stations.

Unmodulated CW- Radar

The transmitted signal of these equipments is constant in amplitude and frequency. These equipment is specialized in speed measuring. Distances cannot be measured. E.g. they are used as speed gauges for police. Newest equipments work in the laser frequency range and measure not only the speed.

Modulated CW- Radar

The transmitted signal is constant in the amplitude but modulated in the frequency. This one gets possible after the principle of the propagation time measurement with that again. It is an advantage of this equipment that an evaluation is carried out without reception break and the measurement result is therefore continuously available. These radar sets are used where the measuring distance isn't too large and it's necessary a continuous measuring (e.g. an altitude measuring in airplanes or as weather radar).

A similar principle is also used by radar sets whose transmitting impulse is too long to get a well distance resolution. Often this equipment modulate its

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transmitting pulse to obtain a distance resolution within the transmitting pulse with the help of the pulse compression.

Classification Depending Upon Technology

Primary Radar

The following figure shows the operating principle of a primary radar set. The radar antenna illuminates the target with a microwave signal, which is then reflected and picked up by a receiving device. The electrical signal picked up by the receiving antenna is called echo or return. The radar signal is generated by a powerful transmitter and received by a highly sensitive receiver.

Block diagram of a primary radar

All targets produce a diffuse reflection i.e. it is reflected in a wide number of directions. The reflected signal is also called scattering. Backscatter is the term given to reflections in the opposite direction to the incident rays.

Radar signals can be displayed on the traditional plan position indicator (PPI) or other more advanced radar display systems. A PPI has a rotating vector with the radar at the origin, which indicates the pointing direction of the antenna and hence the bearing of targets.

Secondary Radar

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Radar was born in the due to the pressure of war. The need to detect “hostile” aircraft led to a vast investment in intellect and money to develop RADAR.

Classical Radar (now called Primary Radar) by definition is a non co-operative technology i.e. it needs no co-operation from the “Target” being detected. Why do we need a different system then? As well as seeing “hostile” aircraft it soon became apparent that Radar was a good tool to see friendly aircraft and hence control and direct them. Large Vertical Aperture Antenna

As well as seeing “hostile” aircraft it soon became apparent that Radar was a good tool to see friendly aircraft and hence control and direct them. If the “friendly” aircraft is fitted with a transponder (transmitting responder), then it sends a strong signal back as an “echo”. An active also encoded response signal which is returned to the radar set then is generated in the transponder. This proved very useful for the military in seeing their own aircraft clearly. In this response can be contained much more information, as a primary radar unit is able to acquire.

CONTINUOUS WAVE RADAR: Continuous wave radars continuously transmit a high-frequency signal and the reflected energy is also received and processed continuously. These radars have to ensure that the transmitted energy doesn’t leak into the receiver (feedback connection). CW radars measures radial velocity of the target using Doppler Effect. If there is relative motion between the radar and the target, the shift in carrier frequency (Doppler shift) of the reflected wave becomes a measure of targets relative velocity. The block diagram of continuous wave radar is shown

25

Block diagram of continuous wave radar

The transmitter generates a continuous oscillations of frequency fo which is radiated by radar antenna. A portion of this radiated energy is intercepted by target and reradiated energy is collected by the receiver antenna. If the target is moving with the velocity Vr relative to the radar, the received signal will be shifted in frequency from the transmitted frequency fo by the amount fd. The plus sign for an approaching target and minus sign for a receding target. The received echo signal (fo±fd) enters the radar via the antenna and is mixed in a detector mixer with a portion of a transmitter signal fo to produce the Doppler frequency fd. The purpose of using a beat frequency amplifier is to eliminate echo from stationary targets and to amplify the Doppler echo signal to a level where it can operate an indicating device such as frequency meter.

ADVANTAGES: 1) It uses low transmitting power, low power consumption.

2) It has simple circuitry and it is small in size.

3) Unlike pulse radar CW radar is able to detect an aircraft inspite of fixed objects.

DISADVANTAGES: 1) Practical application of CW radar is limited by the fact that several targets at a given bearing tend to cause confusion.

2) Range discrimination can be achieved only by introducing very costly complex circuitry.

3) It is not capable of indicating the range of target and can show only its velocity.

CW RADARS TYPES

Unmodulated

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An example of unmodulated CW radar is speed gauges used by the police. The transmitted signal of these equipments is constant in amplitude and frequency. CW radar transmitting unmodulated power can measure the speed only by using the Doppler-effect. It cannot measure a range and it cannot differ between two reflecting objects.

Modulated Unmodulated CW radars have the disadvantage that they cannot measure range, because run time measurements is not possible (and necessary) in unmodulated CW-radars. This is achieved in modulated CW radars using the frequency shifting method. In this method, a signal that constantly changes in frequency around a fixed reference is used to detect stationary objects. Frequency is swept repeatedly between two frequencies. On examining the received reflected frequencies (and with the knowledge of the transmitted frequency), range calculation can be done.

Pulse Radar

Pulse radar sets transmit a high-frequency Impulse signal of high power. After this impulse signal, a longer break follows in which the echoes can be received, before a new transmitted signal is sent out. Direction, distance and sometimes if necessary the height or altitude of the target can be determined from the measured antenna position and propagation time of the pulse-signal.

A monopulse secondary surveillance radar antenna (looks like a lattice fence) mounted on top of an antenna of a primary radar (parabolic reflector)

These classically radar sets transmit a very short pulse (to get a good range resolution) with an extremely high pulse-power (to get a good maximum range).

Pulse Radar using Pulse Compression

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These radar sets transmit a relatively weak pulse with a longer pulse-width. It modulates the transmitting signal to obtain a distance resolution also within the transmitting pulse with help of the pulse-compression.

Monostatic / Bistatic RadarsMonostatic radars are deployed in a single site. Transmitter and receiver are collocated and the radar uses the same antenna mostly. Bistatic radar consists of a separated (by a considerable distance) transmitting and receiving sites.

Classification on the basis of design:

Radar systems may be divided into types based on the designed use. This section presents the general characteristics of several commonly used radar systems:

Classification of radar sets according its use

Although any and every radar can be abused as military radar, the necessary distinction as military or civil radar has legal causes often.

Air-defence Radars

Air-Defence Radars can detect air targets and determine their position, course, and speed in a relatively large area. The maximum range of Air-Defence Radar can exceed 300 miles, and the bearing coverage is a

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complete 360-degree circle. Diagram of Rotating radar pattern

Air-Defence Radars are usually divided into two categories, based on the amount of position information supplied. Radar sets that provide only range and bearing information are referred to as two-dimensional, or 2D, radars. Radar sets that supply range, bearing, and height are called three-dimensional, or 3D, radars. Air-Defence Radars are used as early-warning devices because they can detect approaching enemy aircraft or missiles at great distances. In case of an attack, early detection of the enemy is vital for a successful defence against attack. Antiaircraft defences in the form of antiaircraft artillery (abbreviated to “AAA”) missiles, or fighter planes must be brought to a high degree of readiness in time to repel an attack. Range and bearing information, provided by Air-Defence Radars, used to initially position fire-control tracking radar on a target. Another function of the Air-Defence Radar is guiding combat air patrol (CAP) aircraft to a position suitable to intercept an enemy aircraft. In the case of aircraft control, the guidance information is obtained by the radar operator and passed to the aircraft by either voice radio or a computer link to the aircraft.

Air traffic control   ( ATC )

It is a service provided by ground-based controllers who direct aircraft on the ground and through controlled airspace, and can provide advisory services to aircraft in non-controlled airspace. The primary purpose of ATC worldwide is to prevent collisions, organize and expedite the flow of traffic, and provide information and other support for pilots. 

In some countries, ATC plays a security or defensive role, or is operated by the military. Since radar center control a large airspace area, typically use long range radar that has the capability are used, at higher altitudes, to see Air Surveillance Radar

aircraft within 200 nautical miles (370 km) of the radar antenna.

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SOME RADAR SETS

ROHINI

3DSURVEILLANCE RADAR

The 3D Surveillance Radar is state-of-art radar designed to effectively play the role of medium range surveillance radar mounted on a mobile platform. The radar operates in S-band and is capable of Track-While- Scan [TWS] of airborne targets up to 150 Kms.

SALIENT FEATURES

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3D State of the art medium Range

Surveillance Radar.

TWS of airborne Targets upto 150 Kms.

Configured as three mobile units mounted on three vehicles.

Fully automated and controlled from Radar Console with user friendly GUI.

Dedicated on-line BITE facility.

Data remoting of Tracks and plots over LAN to remote stations.

Data remoting of Digital data Link to remote data center.

ASHLESHA

Low Level Light-Weight Radar (LLLR) is an S-Band, 3D, light weight, battery powered and compact sensor which provides 3D surveillance. This radar

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is with multiple beams and electronic scanning capability in elevation and can be rapidly deployed in various terrains like mountain tops, deserts and even high rise buildings in urban areas to help carryout aerial surveillance at low and medium altitudes. The radar would provide for detection and tracking of all kinds of hostile aerial targets like fighter aircrafts, UAVs and helicopters.

SALIENT FEATURES

S-Band 3D Surveillance of aerial targets flying at low and medium altitudes.

Automatic detection and tracking of:-Fixed wing aircrafts-Helicopter.

Detection of hovering Helicopters.

Low power consumption and mechanical ruggedness to operate in extreme climatic conditions.

Based on semi active array antenna using the state of art Transmit/ Receive Module (TRM) technology.

Integrated IFF.

Easily transportable by men, animal transport, etc.

Highly modular for quick setup.

Robust design and good testability/ maintainability features

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BHARANI

Low Level Light-Weight Radar (LLLR) is a L-Band,2D, light weight, battery powered and compact sensor which provides 2D surveillance solution to alert Army Air Defence Weapon Systems mainly in mountainous terrain against hostile aerial targets like UAVs, RPVs, hovering helicopters and fixed wing aircraft flying at low and medium altitudes.

SALIENT FEATURES

L-Band 2D Surveillance of aerial targets flying at low and medium altitudes.

Automatic detection and tracking of:-Fixed wing aircrafts-Helicopter-UAVs

Detection of hovering Helicopters.

Target designation and distribution to Weapon Sites and Command Centre.

Integrated IFF.

Easily transportable by men, animal transport, etc.

Highly modular for quick setup.

Remote operation and radar display through the Commander's Display Unit (CDU).

Separation of CDU from sensor head: 750 m

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Indra II

INDRA II is L Band low-flying detection radar that caters to the vital gap filling role in an air defence environment. It is a transportable and self-contained system with easy mobility and deployment features. The system consists mainly of an Antenna, Transmitter cabin and Display cabin mounted on three separate vehicles.

SALIENT FEATURES

Fully coherent system

Frequency agility

Pulse compression

Track while scan for 2-D tracking

Capability to handle 200 tracks

Association of primary and secondary targets

Full tracking capabilities for manoeuvring targets

Multicolour PPI Raster Scan Display, presenting both MTI and Synthetic Video

Automatic target data transmission to a digital modem/networking of radars

Ease of transportation and fast deployment.

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3-D TACTICAL CONTROL RADAR

The 3D Tactical Control Radar is state-of-art medium range Surveillance & Tracking radar designed to effectively play the role of medium range surveillance radar mounted on a mobile platform. The radar operates in S-band and is capable of Track-While-Scan [TWS] of airborne targets up to 90 Kms.

SALIENT FEATURES

3D State of the art medium Range Surveillance and Tracking Radar.

TWS of airborne Targets up to 90 Kms.

Side-lobe blanking, Frequency agility and Jammer analysis.

Integrated IFF & co-mounted antenna.

Configured in two TATRA vehicles one for radar and second for power source.

Fully automated and controlled from Radar Console with user friendly GUI.

Dedicated facility.

Facility for training controllers, operators & technical crew.

Facility for automatic transmission of data to Target Data Receiver (co-located with weapon system) up to a distance of 20 Km from radar using optical line, wire line and secure VHF radio set.

Data remoting of Tracks and plots over LAN to external networks - up to 500 m.

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TACTICAL CONTROL RADAR

The Tactical Control Radar is an early warning, alerting and cueing system, including weapon control functions. It is specially designed to be highly mobile and easily transportable, by air as well as on the ground. This radar minimises mutual interference of tasks of both air defenders and friendly air space users. The command and control capabilities of the RADAR in combination with an effective ground based air Defence provide maximum operational effectiveness with a safe, efficient and flexible use of the airspace.

SALIENT FEATURES

All weather day and night capability

40 km range, giving a large coverage

Multiple target handling and engagement capability

Local threat evaluation and engagement calculations assist the commander's decision making process, and give effective local fire distribution.

Easy to operate, and hence low manning requirements and stress reduction under severe conditions

Highly mobile system, to be used in all kinds of terrain, with short into and out of action times (deployment/redeployment)

Clutter suppression

High resolution, which gives excellent target discrimination and allows accurate tracking

RADAR DEVICES

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RADAR ANTENNA

Antenna is a structure which serves as a transition between wave propagating in free space, and the fluctuating voltages in the circuit to which it is connected. An antenna either receives energy from an electromagnetic field or radiates electromagnetic waves produced by a high frequency generator.

Parabolic Antenna

The parabolic dish antenna is the form most frequently used in the radar engineering of installed antenna types. A dish antenna consists of one circular parabolic reflector and a point source situated in the focal point of this reflector. This point source is called “primary feed” or “feed”.

The circular parabolic (parabolic) reflector is constructed of metal, usually a frame covered by metal mesh at the inner side. Parabolic antenna

The width of the slots of the metal mesh has to be less than λ/10. This metal covering forms the reflector acting as a mirror for the radar energy. According to the laws of optics and analytical geometry, for this type of reflector all reflected rays will be parallel to the axis of the parabolic which gives us ideally one single reflected ray parallel to the main axis with no side lobes. The field leaves this feed horn with a spherical wave front. As each part of the wave front reaches the reflecting surface, it is shifted 180 degrees in phase and sent outward at angles that cause all parts of the field to travel in parallel paths.

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Feed (primary radiator)

Reflector (secondary radiator)

The Cassegrain Antenna

A Cassegrain antenna is an antenna in which the feed radiator is mounted at or near the surface of a concave main reflector and is aimed at a convex subreflector. Both reflectors have a common focal point. Energy from the feed unit (a feed horn mostly) illuminates the secondary reflector, which reflects it back to the main reflector, which then forms the desired forward beam.

Principle of a Cassegrain telescope

Slot Antenna

Slot radiators or slot antennas are antennas that are used in the frequency range from about 300 MHz to 25 GHz.

Basic geometry of a slotted waveguide antenna

They are often used in navigation radar usually as an array fed by a waveguide. But also older large phased array antennas used the principle because the slot radiators are a very inexpensive way for frequency scanning arrays. Slot antennas are an about λ/2 elongated slot, and excited in the center.

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Radar Transmitter

A radar transmitter generates RF- energy necessary for scanning the free space. The often very large amount of energy must be modulated in a specific time pattern to obtain a time reference for time Non-linear FM transmitting pulses measurement of the signal

Radar Receiver

The function of the receiver is to take the weak echoes from the antenna system, amplify them sufficiently, detect the pulse envelope, amplify the pulses, and feed them to the indicator. The receivers used in radars are capable of accepting weak echoes and increasing their amplitudes by a factor of 20 or 30 million. Since radar frequencies are not easily amplified, a superheterodyne receiver changes the radio frequency to an intermediate frequency for amplification.

Radar Display

Modern radar systems typically use some sort of faster scan display to produce a map-like image. Early in radar development, numerous circumstances made such displays difficult to produce. People ultimately developed several different display types.

The radar system transmits a single pulse of electromagnetic radiation, a small portion of which backscatter off targets (intended or otherwise) and return to the radar system. The radar receiver converts all received electromagnetic radiation into a continuous electronic analog signal of varying (or oscillating) voltage.

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Radar A- Scope

Principle of operation of an A-scope

The A-scope display, shown in the figure, presents only the range to the target and the relative strength of the echo. Such a display is normally used in weapons control radar systems. The bearing and elevation angles are presented as dial or digital readouts that correspond to the actual physical position of the antenna. The A-scope normally uses an electrostatic-deflection crt. The sweep is produced by applying a sawtooth voltage to the horizontal deflection plates. The electrical length (time duration) of the sawtooth voltage determines the total amount of range displayed on the crt face.

The A- scope display is using in older radar sets only as monitoring oscilloscope. In modern digital radar sets don't exist a similar video signal of the backscatter. The target messages are transmitted to the displays as a digital word. There isn't any possibility to get a synchronizing signal for these asynchronous serial digital signals. Well, the oscilloscope can get an internal trigger only. Therefore it is impossible to analyze the bit sequence with a simple oscilloscope.

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Radar B-Scope

B - Scope

The B-Scope shows a picture like a Cartesian diagram. It provides a 2-D “top down” representation of space. The horizontal axis (abscissa) typically represents the measurement of the azimuth (bearing), and the vertical axis (ordinate) represents the measurement of the range. Signals appear as bright spots.

B-scope displays were common in airborne and fire-control radars in the 1950s and 60s, which were mechanically or electronically scanned from side to side, and sometimes up and down as well. The center of the bearing usually is movable through hand wheels in fire-control radars. The antenna turntable then is turned into the new direction. The screens middle is defined as the main reception direction of the antenna normally. The bearing area is covered through an electro-mechanical or electronic beam steering.

The used designation “B-scope” is ambiguous sometimes. The term refers to two completely different types of scopes. In radar devices without measurement of the azimuth angle, the term “B-scope” is also used (e.g.: Ground Penetration Radars). The abscissa is a time coded scale then, and shows a history of the pulse periods.

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PLAN-POSITION INDICATOR

It is an intensity-modulation type display system which indicates both range and azimuthal angle of the target simultaneously in polar coordinates. The demodulated echo signal from the receiver is applied to the grid of the CRT which is biased slightly beyond cut-off. Only when blips corresponding to the targets occur, a sawtooth current applied to a pair of coils (on the opposite of the neck of the tube) flows. Thus, a beam is made to deflect radially outward from the centre and also continuously around the tube at the same angular velocity as that of the antenna. The brightness spot at any point on the screen indicates the presence of an object there. Plan Position Indicator

The distance of the bright spot radiating outward from the centre gives the range or the distance of the target from the radar transmitter while the direction in which the spot deflects at certain instant corresponds to the direction of radar antenna (i.e. target direction) at that instant. Thus a map-like presentation is obtained in true relationship to the polar-coordinates of the target scanned.

Normally PPI screens are circular with a diameter of 30 cm or 40 cm. Long-persistence phosphorous are used to ensure that the PPI screen does not flicker. Scanning speed is rather low (compared to the 60 fields/sec in TV), so that various portions of the screen do not get dim between successive scans. The resolution of the screen depends on the bandwidth of the antenna, pulse width, the transmitter frequency and diameter of CRT beam.

Distortion of true map position will occur if PPI is used on an aircraft and its antenna is not pointing straight down. Then computer processing is used to correct for radar altitude, thus converting slant range into true range. However it is expensive. PPI displays are used in search radars and especially when conical scanning is employed.

With modern computer graphics, all of the displays could be made available on a single screen either in time multiplexed form or in split screen presentation format. Advanced concepts such as holographic display could become a reality that would provide true 3-D displays.

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Future Research:

The focus is in the use of radar for surveillance and environmental Electrical

and Electronic Engineering and the Discipline of Physics in the School of

Science together with various external organizations such as the Australian

Defence Science and Technology Organisation, the Bureau of Meteorology, the

Australian Antarctic Division and commercial companies such as Raytheon

Australia.

Key research themes in the Centre are in the area of radar systems and

technology, RF propagation and radar signal processing. The applications focus

for the Centre's research will be the areas of environmental and atmospheric

monitoring through radar sensing, surveillance and radar systems design.

Radar technology currently used to support tactical operations aboard Navy ships will soon be adapted for a new purpose – weather detection. This state-of-the-art phased array radar technology may help forecasters of the future provide

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CONCLUSION

The six weeks of summer training at BEL, Ghaziabad unit generated a lot more interest in my subject.

It made me more aware of the scope of Electronics & Communication Engineering. It has also made me appreciative of an industrial work environment.

Undergoing training on the indoor substation has helped me integrate conceptual knowledge with real life application. I was fortunate to have personal guidance from experienced professionals who took been interest in explaining the working details of various equipments.

I feel that without this opportunity, my own understanding of this subject and also the motivation to acquire more knowledge would have remained incomplete. Well, regarding future scope I think my training has given me enough motivation and an exposure that I will try to join defence services or get linked up with the defence of the country.

“To know the technical know-how, industrial training is the best way to move forward.”

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BIBLIOGRAPHY

[1] THE MAIN RESOURCES OF THE WORK WERE THE FACULTY OF HRD DEPARTMENT.

[2] WEBSITE:

http://www.bel-india.com http://www.radartutorial.eu/01.basics/radar%20Principle.en.html

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