(31st MAY – 09th JULY 2011)

INDUSTRIAL TRAINING REPORT

ON REPORTER RADAR TRANSMITTER

AND

VARIOUS ROTATIONAL PROGRAMS

Submitted By:-

PRATEEK AGGARWAL

Branch- ECE

UPT No.- 125/B.TECH/2011

Roll No.- 09102297

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ACKNOWLEDGEMENT

I wish to express my sincere thanks to the Management of Bharat Electronics

Limited (BEL), Bharat Nagar, Ghaziabad including the Head of the Human

Resource Development Department Mrs. VANITA BHANDARI

(MANAGER, HRD) for providing me an opportunity to receive training in this

important Industrial Unit manufacturing electronics equipment in our country.

I am deeply indebted to Mr. DHYAN SINGH , (Deputy General Manager,

Radar Division PA-R2) AND Mr. A.K. SAKSENA (Manager,PA-R2) for

sparing his most special time in providing guidance to me in training. Without

his wise counsel, inestimable encouragement, it would have been difficult for

me to have knowledge of the functioning of various types of electronics

equipment particularly radars. Gratitude is also due to him for his constant

guidance and direction in writing this piece of work.

Special thanks to Mr. DINESH KUMAR (Department of Radar Transmitter)

for their valuable guidance, help and cooperation.

It is a great pleasure to express my heart full thanks to staff of BEL who helped

me directly or indirectly throughout the successful completion of my training.

There is no substitution to ‘Team Work’; this is one of the lessons I learnt

during my training in BHARAT ELECTRONICS LIMITED.

C

ERTIFICATE

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This is to certify that PRATEEK AGGARWAL of B.TECH 2ND

YEAR(ECE) of JIIT , NOIDA has successfully completed his industrial

training under guidance of Mr. A.K.Saxena, Manager(PA-RADAR) and

Mr. Dinesh Kumar in BHARAT ELECTRONICS LIMITED, GHAZIABAD

from 31th may to 9th july 2011.

A project titled STUDY OF TRANSMITTER OF RADAR was

assigned to him in this period. He worked hard and diligently and completed his

project in time. He took lot of initiative in learning about RADAR SYSTEM

AND VARIOUS TEST INSTRUMENTS/METHODS. His overall

performance during the project was excellent. We wish him all success in his

career.

Mr.Dinesh kumar Mr. A.K.Saxena

___________ Manager

(PA-RADAR2) (PA-RADAR2)

PREFACE

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With the ongoing revolution in electronics and communication where

innovations are taking place at the blink of eye, it is impossible to keep pace

with the emerging trends.

Excellence is an attitude that the whole of the human race is born with. It is the

environment that makes sure that whether the result of this attitude is visible or

otherwise. A well planned, properly executed and evaluated industrial training

helps a lot in collating a professional attitude. It provides a linkage between a

student and industry to develop an awareness of industrial approach to problem

solving, based on a broad understanding of process and mode of operation of

organization.

During this period, the student gets the real experience for working in the

industry environment. Most of the theoretical knowledge that has been gained

during the course of their studies is put to test here. Apart from this the student

gets an opportunity to learn the latest technology, which immensely helps in

them in building their career.

I had the opportunity to have a real experience on many ventures, which

increased my sphere of knowledge to great extent. I got a chance to learn many

new technologies and also interfaced too many instruments. And all this credit

goes to organization BHARAT ELECTRONICS LIMITED.

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CONTENTS

S.No. Topics Page Nos.

1 BEL

Introduction 5-8

2 Manufacturing Units 9-10

3 BEL (Ghaziabad Unit) 11

4 Product Ranges 12

5 Services of BEL 13

6 Rotation Program 14

Test Equipment and Automations

PCB Fabrication

Quality Control Works-Radar

Work Assembly-Communication

Magnetics

Microwave Lab

7 Radar 22

11 Signal Processing Unit 41

12 Fully Coherent Radar 45

13 Magnetron 48

14 Conclusion 55

BHARAT ELECTRONICS LIMITED

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INTRODUCTION

India, as a country, has been very lucky with regard to the introduction of telecom

products. The first telegraph link was commissioned between Calcutta and Diamond Harbor

in the year 1852, which was invented in 1876. First wireless communication equipment were

introduced in Indian Army in the year 1909 with the discovery of Radio waves in 1887 by

Hertz and demonstration of first wireless link in the year 1905 by Marconi and Vacuum

Tube in 1906. Setting up of radio station for broadcast and other telecom facilities almost

immediately after their commercial introduction abroad followed this. After independence of

India in 1947 and adoption of its constitution in 1950, the government was seized with the

plans to lay the foundations of a strong, self-sufficient modern India. On the industrial front,

Industrial Policy Resolution (IPR) was announced in the year 1952. It was recognized that in

certain core sectors infrastructure facilities require huge investments, which cannot be met by

private sector and as such the idea of Public Sector Enterprises (PSE) was mooted. With

telecom and electronics recognized among the core sectors, Indian Telephone Industry, now

renamed as ITI Limited, was formed in 1953 to undertake local manufacture of telephone

equipment, which were of electro-mechanical nature at that stage. Hindustan Cable Limited

was also started to take care of telecom cables.

Bharat Electronics Limited (BEL) was established in 1954 as a public

Sector Enterprise under the administrative control of Ministry of Defence as the fountainhead

to manufacture and supply electronics components and equipment. BEL, with a noteworthy

history of pioneering achievements, has met the requirement of state-of-art professional

electronic equipment for Defence, broadcasting, civil Defence and telecommunications as

well as the component requirement of entertainment and medical X-ray industry. Over the

years, BEL has grown to a multi-product, multi-unit, and technology driven company with

track record of a profit earning PSU.

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The company has a unique position in India of having dealt with all the generations of

electronic component and equipment. Having started with a HF receiver in collaboration with

T-CSF of France, the company’s equipment designs have had a long voyage through the

hybrid, solid-state discrete component to the state of art integrated circuit technology. In the

component arena also, the company established its own electron value manufacturing facility.

It moved on to semiconductors with the manufacture of germanium and silicon devices and

then to the manufacture of Integrated circuits. To keep in pace with the component and

technology, its manufacturing and products assurance facilities have also undergone sea

change. The design groups have CADD facility; the manufacturing has CNC machines and a

Mass Manufacture Facility. QC checks are preformed with multi-dimensional profile

measurement machines, Automatic testing machines, environmental labs to check extreme

weather and other operational conditions. All these facilities have been established to meet

the stringent requirements of MIL grade systems.

Today BEL’s infrastructure is spread over nine locations with 29 production divisions

having ISO-9001/9002 accreditation. Product mix of the company are spread over the entire

Electro-magnetic (EM) sp 3ectrum ranging from tiny audio frequency semiconductor to huge

radar systems and X-ray tubes on the upper edge of the spectrum. Its manufacturing units

have special focus towards the products ranges like Defence Communication, Rader’s,

Optical & Opto-electronics, Telecommunication, sound and Vision Broadcasting, Electronic

Components, etc.

Besides manufacturing and supply of a wide variety of products, BEL offers a variety

of services like Telecom and Rader Systems Consultancy, Contract Manufacturing,

Calibration of Test & Measuring Instruments, etc. At the moment, the company is installing

MSSR radar at important airports under the modernization of airports plan of National

Airport Authority (NAA).

BEL has nurtured and built a strong in-house R&D base by absorbing technologies

from more than 50 leading companies worldwide and DRDO Labs for a wide range of

products. A team of more than 800 engineers is working in R&D. Each unit has its own R&D

Division to bring out new products to the production lines. Central Research Laboratory

(CRL) at Bangalore and Ghaziabad works as independent agency to undertake contemporary

design work on state-of-art and futuristic technologies. About 70% of BEL’s products are of

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in-house design.

BEL was among the first Indian companies to manufacture computer parts and

peripherals under arrangement with International Computers India Limited (ICIL) in 1970s.

BEL assembled a limited number of 1901 systems under the arrangement with ICIL.

However, following Government’s decision to restrict the computer manufacture to ECIL,

BEL could not progress in its computer manufacturing plans. As many of its equipment were

microprocessor based, the company, Continued to develop computers based application, both

hardware and software. Most of its software requirements are in real time. EMCCA, software

intensive navel ships control and command system is probably one of the first projects of its

nature in India and Asia.

BEL has won a number of national and international awards for Import Substitution,

Productivity, Quality, Safety, Standardization etc. BEL was ranked No. 1 in the field of

Electronics and 46th overall among the top 1000 private and public sector undertakings in

India by the Business Standard in its special supplement “The BS 1000 (1997-98)”. BEL was

listed 3rd among the Mini Rattan’s (Category II) by the Government of India, 49th among

Asia’s top 100 worldwide Defence Companies by the Defence News, USA.

CORPORATE MOTTO , MISSION AND OBJECTIVES:

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The passionate pursuit of excellence at BEL is reflected in a reputation with its

customers that can be described in its motto, mission and objectives:

CORPORATE MOTTO

“Quality, Technology and Innovation.”

CORPORATE MISSION

To be the market leader in Defence Electronics and in other chosen fields and products.

CORPORATE OBJECTIVES

To become a customer-driven company supplying quality products at competitive prices

at the expected time and providing excellent customer support.

To achieve growth in the operations commensurate with the growth of professional

electronic industry in the country.

To generate internal resources for financing the investments required for modernization,

expansion and growth for ensuring a fair return to the investor.

In order to meet the nations strategic needs, to strive for self-reliance by indigenization of

materials and components.

To retain the technological leadership of the company in Defence and other chosen fields

of electronics through in-house research and development as well as through

Collaboration/Co-operation with Defence/National Research Laboratories, International

Companies, Universities and Academic Institutions.

To progressively increase overseas sales of its products and services.

To create an organizational culture which encourages members of the organization to real

and through continuous learning on the job

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MANUFACTURING UNITSMANUFACTURING UNITS

BANGALORE (KANARATAKA)

BEL started its production activities in Bangalore on 1954 with 400W high frequency

(HF) transmitter and communication receiver for the Army. Since then, the Bangalore

Complex has grown to specialize in communication and Radar/Sonar Systems for the Army,

Navy and Air-force.

BEL’s in-house R&D and successful tie-ups with foreign Defence companies and

Indian Defence Laboratories has seen the development and production of over 300 products

in Bangalore alone. The Unit has now diversified into manufacturing of electronic products

for the civilian customers such as DoT, VSNL, AIR and Doordarshan, Meteorological Dept.,

ISRO, Police, Civil Aviation and Railways. As an aid to Electorate, the unit has developed

Electronic Voting Machines that are produced at its Mass Manufacturing Facility (MMF).

GHAZIABAD (UTTER PRADESH)

The second largest Unit at Ghaziabad was set up in 1974 to manufacture special types

of radar for the Air Defence Ground Environment Systems (Plan ADGES). The Unit provides

Communication Systems to the Defence Forces and Microwave Communication Links to the

various departments of the State and Central Govt. and other users. The Unit’s product range

included Static and Mobile Radar, Tropo scatter equipment, professional grade Antennae and

Microwave components.

PUNE (MAHARASHTRA)

This Unit was started in 1979 to manufacture Image Converter Tubes. Subsequently,

Magnesium Manganese-dioxide Batteries, Lithium Sulphur Batteries and X-ray Tubes/Cables

were added to the product range. At the present the Laser Range Finders for the Defence

services.

MACHILIPATNAM (ANDHRA PRADESH)

The Andhra Scientific Co. at Machilipatnam, manufacturing Optics/Opto-electronic

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equipment was integrated with BEL in 1983. the product line includes passive Night Vision

Equipment, Binoculars and Goggles, Periscopes, Gun Sights, Surgical Microscope and

Optical Sights and Mussel Reference Systems for tank fire control systems. The Unit has

successfully diversified to making the Surgical Microscope with zoom facilities.

PANCHKULA (HARYANA)

To cater the growing needs of Defence Communications, this Unit was established in

1985. Professional grade Radio-communication Equipment in VHF and UHF ranges entirely

developed by BEL and required by the Defence services are being met from this Unit.

CHENNAI (TAMIL NADU)

In 1985, BEL established another Unit at Chennai to facilitate manufacture of Gun

Control Equipment required for the integration and installation and the Vijay anta tanks. The

Unit is now manufacturing Stabilizer Systems for T-72 tanks, Infantry Combat Vehicles

BMP-II; Commander’s Panoramic Sights & Tank Laser Sights are among others.

KOTDWARA (UTTER PRADESH)

In 1986, BEL STARTED A unit at Kotdwara to manufacture Telecommunication

Equipment for both Defence and civilian customers. Focus is being given on the

requirement of the Switching Equipment.

TALOJA (MAHARASHTRA)

For the manufacture of B/W TV Glass bulbs, this plant was established in

collaboration with coming, France in 1986. The Unit is now fully mobilized to manufacture

HYDERABAD (ANDHRA PRADESH)

To coordinate with the major Defence R&D Laboratories located in Hyderabad,

DLRL, DRDL and DMRL, BEL established a Unit at Hyderabad in 1986. Force Multiplier

Systems are manufactured here for the Defence services 20’’ glass bulbs indigenously.

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BEL GHAZIABAD UNIT

Formation

In the mid 60’s, while reviewing the Defence requirement of the country, the

government focused its attention to strengthen the Air Defence system, in particular the

ground electronics system support, for the air Defence network. This led to the formulation of

a very major plan for an integrated Air Defence Ground Environment System known as the

plan ADGES with Prime Minister as the presiding officer of the apex review committee .At

about the same time, Public attention was focused on the report of the Bhabha committee on

the development and production of electronic equipment. The ministry of Defence

immediately realized the need to establish production capacity for meeting the electronic

equipment requirements for its plan ADGES.

BEL was then inserted with the task of meeting the development and production

requirement for the plan ADGES and in view of the importance of the project it was decided

to create additional capacity at a second unit of the company.

In December 1970 the Govt. sanctioned an additional unit for BEL. In 1971, the

industrial license for manufacture of radar and microwave equipment was obtained, 1972 saw

the commencement of construction activities and production was launched in 1974.

Over the years, the unit has successfully manufactured a wide variety of equipment

needed for Defence and civil use. It has also installed and commissioned a large number of

systems on turnkey basis. The unit enjoys a unique status as manufacture of IFF systems

needed to match a variety of primary raiders. More than 30 versions of IFF’s have already

been supplied traveling the path from vacuum technology to solid-state to latest Microwave

Component based system.

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PRODUCT RANGES

The product ranges today of the company are:

RADAR SYSTEMS

3-Dimensional High Power Static and Mobile Radar for the Air Force.

Low Flying Detection Radar for both the Army and the Air force.

Tactical Control Radar System for the Army.

Battlefield Surveillance Rader for the Army.

IFF Mk-X Radar systems for the Defence and export.

ASR/MSSR systems for Civil Aviation.

Radar & allied systems Data Processing Systems.

COMMUNICATIONS

Digital Static Tropo scatters Communication Systems for the Air Force.

Digital Mobile Tropo scatters communication System for the Air Force and Army.

VHF, UHF & Microwave Communication Equipment.

Bulk Encryption Equipment.

Turnkey communication Systems Projects for Defence & civil users.

Static and Mobile Satellite Communication Systems for Defence.

Telemetry /Tele-control Systems.

ANTENNA

Antennae for Radar, Terrestrial & Satellite Communication Systems.

Antennae for TV Satellite Receive and Broadcast applications.

Antennae for Line-of-sight Microwave Communication Systems.

MICROWAVE COMPONENT

Active Microwave components like LNAs, Synthesizer, and Receivers etc.

Passive Microwave components like Double Balanced Mixers, etc.

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SERVICES OF BHARAT ELECTRONICS LIMITED (BEL):-

DEFENCE PRODUCTS:-

Naval System

Military Communication Equipment

Radars

Tele Communication & Broadcasting Services

Opto Electronics

Electronic Warfare

Tank Electronics

NON-DEFENCE PRODUCTS:-

Electronic Voting Machine

Solar Products

Simputer

DTH

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ROTATION PROGRAM

Under this students are introduced to the company by putting them under a

rotation program to various departments. The several departments where I had gone

under my rotational program are:

1. Test Equipment and Automation

2. Quality Control Works-Radar

3. Work Assembly- Communication

4. Microwave lab

Rotation period was to give us a brief insight of the company’s functioning and

knowledge of the various departments. A brief idea of the jobs done at the particular

departments was given. The cooperative staff at the various departments made the

learning process very interesting , which allowed me to know about the company in a

very short time.

TEST EQUIPMENT AND AUTOMATION

This department deals with the various instruments used in BEL. There are 300

equipments and they are of 16 types.

Examples of some test equipments are:

Oscilloscope(CRO)

Multimeter

Signal Analyzer

Logical Pulsar

Counter

Function Generator etc.

Mainly the calibration of instruments is carried out here. They are compared with the

standard of National Physical Laboratory (NPL). So, it is said to be one set down to NPL. As

every instrument has a calibration period after which the accuracy of the instrument falls

from the required standards. So if any of the instruments is not working properly, it is being

sent here for its correct calibration. To calibrate instruments software techniques are used

which includes the program written in any suitable programming language. So it is not the

15

calibration but programming that takes time .For any industry to get its instrument calibrated

by NPL is very costly, so it is the basic need for every industry to have its own calibration

unit if it can afford it.

Test equipment and automation lab mainly deals with the equipment that is used for

testing and calibration .The section calibrates and maintains the measuring instruments

mainly used for Defence purpose.

A calibration is basically testing of equipment with a standard parameter. It is done

with the help of standard equipment should be of some make, model and type.

The national physical laboratory (NPL), New Delhi provides the standard values

yearly. BEL follows International Standard Organization (ISO) standard. The test equipments

are calibrated either half yearly or yearly.

After testing different tags are labeled on the equipment according to the observations.

1. Green –O.K , Perfect

2. Yellow – Satisfactory but some trouble is present.

3. Red – Can’t be used, should be disposed off.

The standard for QC, which are followed by BEL are:

1. WS 102

2. WS 104

3. PS 520

4. PS 809

5. PS 811

6. PS 369

Where, WS = Workmanship & PS = Process Standard

After the inspection of cables, PCB’s and other things the defect found are given in following

codes.

A --- Physical and Mechanical defects.

B --- Wrong Writing

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C --- Wrong Component / Polarity

D --- Wrong Component / Mounting

E --- Bad Workmanship/ Finish

F --- Bad Soldering

G --- Alignment Problem

H --- Stenciling

I --- Others (Specify)

J --- Design & Development

After finding the defect, the equipment is sent to responsible department

which is rectified there.

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QUALITY CONTROL

According to some laid down standards, the quality control department ensures the

quality of the product. The raw materials and components etc. purchased and inspected

according to the specifications by IG department. Similarly QC work department inspects all

the items manufactured in the factory. The fabrication department checks all the fabricated

parts and ensures that these are made according to the part drawing, painting , plating and

stenciling etc are done as per BEL standards.

The assembly inspection departments inspects all the assembled parts such as PCB ,

cable assembly ,cable form , modules , racks and shelters as per latest documents and BEL

standards .

The mistakes in the PCB can be categorized as:

D & E mistakes

Shop mistakes

Inspection mistakes

The process card is attached to each PCB under inspection. Any error in the PC is

entered in the process card by certain code specified for each error or defect.

After a mistake is detected following actions are taken:

1. Observation is made.

2. Object code is given.

3. Division code is given.

4. Change code is prepared.

5. Recommendation action is taken

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WORK ASSEMBLYWORK ASSEMBLY

This department plays an important role in the production. Its main function is to

assemble various components, equipments and instruments in a particular procedure.

It has been broadly classified as:

WORK ASSEMBLY RADAR e.g. INDRA –II, REPORTER.

WORK ASSEMBLY COMMUNICATION e.g. EMCCA, MSSR, MFC.

EMCCA: EQUIPMENT MODULAR FOR COMMAND CONTROL APPLICATION.

MSSR: MONOPULSE SECONDARY SURVEILLANCE RADAR.

MFC: MULTI FUNCTIONAL CONSOLE.

The stepwise procedure followed by work assembly department is:

o Preparation of part list that is to be assembled.

o Preparation of general assembly.

o Schematic diagram to depict all connections to be made and brief idea about all components.

o Writing lists of all components.

In work assembly following things are done :

M aterial Receive :

Preparation- This is done before mounting and under takes two procedures.

Tinning- The resistors ,capacitors and other components are tinned with the help of tinned

lead solution .The wire coming out from the components is of copper and it is tinned nicely

by applying flux on it so that it does not tarnished and soldering becomes easy.

Bending- Preparation is done by getting the entire documents , part list drawing and bringing

all the components before doing the work.

Mounting- It means soldering the components of the PCB plate with the help of soldering

tools. The soldering irons are generally of 25 W and are of variable temperature, one of the

wires of the component is soldered so that they don’t move from their respective places on

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the PCB plate. On the other hand of the component is also adjusted so that the PCB does not

burn.

Wave Soldering- This is done in a machine and solder stick on the entire path, which are

tinned.

Touch Up- This is done by hand after the finishing is done.

Cleaning:

Inspection- This comes under quality work.

Heat Ageing- This is done in environmental lab at temperature of 40 degree C for 4 hrs and

three cycles.

Testing:

Lacquering- This is only done on components which are not variable.

Storing- After this variable components are sleeved with Teflon. Before Lacquering mounted

plate is cleaned with isopropyl alcohol. The product is then sent to store.

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MICROWAVE LABORATORY

Microwave lab deals with very high frequency measurements or very short

wavelength measurements. The testing of microwave components is done with the help of

various radio and communication devices. Phase and magnitude measurements are done in

this section. Power measurements are done for microwave components because current and

voltage are very high at such frequencies.

Different type of waveguides is tested in this department like rectangular waveguides,

circular waveguides. These waveguides can be used to transmit TE mode or TM mode. This

depends on the users requirements. A good waveguide should have fewer loses and its walls

should be perfect conductors.

In rectangular waveguide there is min. distortion. Circular waveguides are used where

the antenna is rotating. The power measurements being done in microwave lab are in terms of

S- parameters. Mainly the testing is done on coupler and isolators and parameters are tested

here.

There are two methods of testing:

a.) Acceptance Test Procedure(ATP)

b.) Production Test Procedure(PTP)

Drawing of various equipments that are to be tested is obtained and testing is

performed on manufactured part. In the antenna section as well as SOHNA site various

parameters such as gain ,bandwidth ,VSWR , phase ,return loss, reflection etc. are checked.

The instruments used for this purpose are as follow:

i) Filters

ii) Isolators

iii) Reflectors

iv) Network Analyzers

v) Spectrum Analyzers

vi) Amplifiers and Accessories

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RADAR

History of RADAR

Nobody can be credited with "inventing" radar. The idea had been around for a long

time--a spotlight that could cut through fog. But the problem was that it was too advanced for

the technology of the time. It wasn't until the early 20th century that a radar system was first

built. One of the biggest advocators of radar technology was Robert Watson-Watt, a British

scientist.

Great Britain made a big effort to develop radar in the years leading up to World War

Two. Some people credit them with being pioneers in the field. As it was, the early warning

radar system (called "Chain Home") that they built around the British Isles warned them of

all aerial invasions. This gave the outnumbered Royal Air Force the edge they needed to

defeat the German Luftwaffe during the Battle of Britain.

While radar development was pushed because of wartime concerns, the idea first

came about as an anti-collision system. After the Titanic ran into an iceberg and sank in 1912,

people were interested in ways to make such happenings avoidable

Introduction

The term RADAR was coined in 1941 as an acronym for Radio Detection and

Ranging. This acronym of American origin replaced the previously used British abbreviation

RDF (Radio Direction Finding).

Radar is a system that uses radio waves to detect, determine the distance or speed,

objects such as aircraft, ships, rain and map them. Speed detection is measured by the amount

of Doppler Effect frequency shift of the reflected signal. A transmitter emits radio waves,

which are reflected by the target, and detected by a receiver, typically in the same location as

the transmitter. Although the radio signal returned is usually very small, radio signals can

easily be amplified, so radar can detect objects at ranges where other emission, such as sound

or visible light, would be too weak to detect. Radar is used in many contexts, including

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meteorological detection of precipitation, air traffic control, police detection of speeding

traffic, and by the military.

Several inventors, scientists, and engineers contributed to the development of radar.

The use of radio waves to detect "the presence of distant metallic objects via radio waves"

was first implemented in 1904 by Christian Hülsmeyer, who demonstrated the feasibility of

detecting the presence of ships in dense fog and received a patent for radar as Reichspatent

Nr. 165546. Another of the first working models was produced by Hungarian Zoltán Bay in

1936 at the Tungsram laboratory

BASIC PRINCIPLE

Echo and Doppler Shift

Echo is something you experience all the time. If you shout into a well or a canyon,

the echo comes back a moment later. The echo occurs because some of the sound waves in

your shout reflect off of a surface (either the water at the bottom of the well or the canyon

wall on the far side) and travel back to your ears. The length of time between the moments

you shout and the distance between you and the surface that creates the echo determines the

moment that you hear the echo.

Doppler shift is also common. You probably experience it daily (often without

realizing it). Doppler shift occurs when sound is generated by, or reflected off of, a moving

object. Doppler shift in the extreme creates sonic booms (see below). Here's how to

understand Doppler shift (you may also want to try this experiment in an empty parking lot).

Let's say there is a car coming toward you at 60 miles per hour (mph) and its horn is blaring.

You will hear the horn playing one "note" as the car approaches, but when the car passes you

the sound of the horn will suddenly shift to a lower note. It's the same horn making the same

sound the whole time. The change you hear is caused by Doppler shift.

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HOW RADAR WORKS

A radar system, as found on many merchants’ ships, has three main parts:

1. The antenna unit or the scanner

2. The transmitter receiver or ‘transceiver’ and

3. the visual display unit

The antenna is two or three meter wide and focuses pulses off very high frequency

radio energy into a narrow vertical beam. The frequency of the radio waves is basically about

10,000 Mhz. The antenna is rotated at the rate of 10 to 25 rpm so that radar beam swaps

through 300degree Celsius all around the shiout to a range of about 90 kms.

In all radar it is vital that the transmitting and the receiving in a transceiver are in

close harmony. Every thing depends on accurate measurement of the time that passes

between the transmission of pulse and the return of the echo. About 1000, pulses per second

are transmitted. Though it is varied to suit the requirements. Short pulses are best for short-

range work, longer pulses are best for longer-range work.

An important part of transceiver circuit is ‘modular circuit’. This ‘keys’ the

transmitter so that it oscillates, or pulses for the right length of time. The pulses so designed

are ‘video pulses. These pulses are short range pulses hence can’t serve out the purpose of

long range work .In order to modify these pulses to long range pulses or the RF pulses, we

need to generate the power. The transmitted power is generated in a device called the

“magnetron” which can handle all these short pulses and very high oscillations.

The display system usually carried out the control necessary for the operation of

whole radar .It has a cathode ray gun, which consists of a electron gun in its neck. The gun

shouts electron to the phosphorescent screen at the far end. Phosphorescent screen glows

when hit by an electron and the resulting spot can be seen through the glass face.

The basic idea behind radar is very simple: a signal is transmitted, it bounces off an

object and some type of receiver later receives it.  They use certain kinds of electromagnetic

waves called radio waves and microwaves.  This is where the name RADAR comes from

(Radio Detection And Ranging).  Sound is used as a signal to detect objects in devices called

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SONAR (Sound Navigation Ranging).  Another type of signal used that is relatively new is

laser light that is used in devices called LIDAR (Light Detection And Ranging). 

           Once the radar receives the returned signal, it calculates useful information from it

such as the time taken for it to be received, the strength of the returned signal, or the change

in frequency of the signal. 

Basic Radar System:

A basic radar system is spilt up into a transmitter, switch, antenna, receiver, data

recorder, processor and some sort of output display.  Everything starts with the transmitter as

it transmits a high power pulse to a switch, which then directs the pulse to be transmitted out

an antenna. Once the signals are received the switch then transfers control back to the

transmitter to transmit another signal.  The switch may toggle control between the transmitter

and the receiver as much as 1000 times per second.

Any received signals from the receiver are then sent to a data recorder for

storage on a disk or tape.  Later the data must be processed to be interpreted into

something useful, which would go on a Pulse Width and Bandwidth:

Some radar transmitters do not transmit constant, uninterrupted electromagnetic

waves.  Instead, they transmit rhythmic pulses of EM waves with a set amount of time in

between each pulse.  The pulse itself would consist of an EM wave of several wavelengths

with some dead time after it in which there are no transmissions.  The time between each

pulse is called the pulse repetition time (PRT) and the number of pulses transmitted in one

25

second is called the pulse repetition frequency (PRF).  The time taken for each pulse to be

transmitted is called the pulse width (PW) or pulse duration.  Typically they can be around

0.1 microseconds long for penetrating radars or 10-50 microseconds long for imaging radars

(a display. microsecond is a millionth of a second).

In math language, the above can be said...

PRT = 1 / PRF

or

PRF = 1 / PRT

And for all you visual learners out there, this is what it looks like...

RT means repetition time .

However, the above diagram is not quite realistic for several reasons.  One reason

why it is not realistic is that the frequency in waves of the pulses is the same.  In real life the

frequency of the waves are not the same and they change as time goes on.   This is called

frequency modulation, which means the frequency changes or modulates.

It looks something like this...

26

Think of this as one pulse.  All the pulses will look something like this.

On the above diagram, the frequency of the wave is low on the left and it slowly

increases, as you look right.  The different frequencies of the wave will lie in a range called

bandwidth.  Radars use bandwidth for several reasons regarding the resolution of a data

image, memory of the radar and overuse of the transmitter.  For instance, a high bandwidth

can yield a finer resolution but take up more memory. When an EM wave hits a surface, it

gets partly reflected away from the surface and refracted into the surface.  The amount of

reflection and refraction depends on the properties of the surface and the properties of the

matter, which the wave was originally traveling through.  This is what happens to radar

signals when they hit objects.  If a radar signal hits a surface that is perfectly flat then the

signal gets reflected in a single direction (the same is true for refraction).  If the signal hits a

surface that is not perfectly flat (like all surfaces on Earth) then it gets reflected in all

directions.  Only a very small fraction of the original signal is transmitted back in the

direction of the receiver.  This small fraction is what is known as backscatter.  The typical

power of a transmitted signal is around 1 kilowatt and the typical power of the backscatter

can be around 10 watts.

TYPES OF RADAR

Based on function radar can be divided into two types:

1. PRIMARY RADAR2. SECONDRY RADAR

Primary radar or the simple radar locates a target by procedure described in section.

But in cases as controlling of air traffic, the controller must be able to identify the aircraft and

find whether it is a friend or foe. It is also desired to know the height of aircraft.

To give controller this information second radar called the secondary surveillance

radar (SSR) is used. This works differently and need the help of the target aircraft it séance

out a sequence of pulses to an electronic BLACK BOX called the TRANSPONDER, fitted

on the aircraft. The transponder is connected to the aircrafts altimeter (the device which

measures the planes altitude) to transmit back the coded message to the radar about its status

and altitude. Military aircrafts uses a similar kind of radar system with secrete code to make

27

sure that it is friend or foe, a hostile aircraft does not know what code to transmit back to the

ground station for the corresponding receiver code.

RADAR EQUATION

The amount of power Pr returning to the receiving antenna is given by the radar equation:

where

Pt = transmitter power

Gt = gain of the transmitting antenna

Ar = effective aperture (area) of the receiving antenna

σ = radar cross section, or scattering coefficient, of the target

F = pattern propagation factor

Rt = distance from the transmitter to the target

Rr = distance from the target to the receiver.

In the common case where the transmitter and the receiver are at the same location, Rt

= Rr and the term Rt2 Rr

2 can be replaced by R4, where R is the range. This yields:

This shows that the received power declines as the fourth power of the range, which

means that the reflected power from distant targets is very, very small.

The equation above with F = 1 is a simplification for vacuum without interference.

The propagation factor accounts for the effects of multipath and shadowing and depends on

the details of the environment. In a real-world situation, pathloss effects should also be

considered.

28

RADAR SIGNAL PROCESSING

Distance measurement

Transit time

Principle of radar distance measurement using pulse round trip time.

One way to measure the distance to an object is to transmit a short pulse of radio

signal, and measure the time it takes for the reflection to return. The distance is one-half the

product of round trip time (because the signal has to travel to the target and then back to the

receiver) and the speed of the signal. where c is the speed of light in a vacuum,

and τ is the round trip time. For radar, the speed of signal is the speed of light, making the

round trip times very short for terrestrial ranging. Accurate distance measurement requires

high-performance electronics.

The receiver cannot detect the return while the signal is being sent out – there is no

way to tell if the signal it hears is the original or the return. This means that a radar has a

distinct minimum range, which is the length of the pulse multiplied by the speed of light,

divided by two. In order to detect closer targets one must use a shorter pulse length.

A similar effect imposes a specific maximum range as well. If the return from the

target comes in when the next pulse is being sent out, once again the receiver cannot tell the

difference. In order to maximize range, one wants to use longer times between pulses, the

inter-pulse time.

29

These two effects tend to be at odds with each other, and it is not easy to combine

both good short range and good long range in a single radar. This is because the short pulses

needed for a good minimum range broadcast have less total energy, making the returns much

smaller and the target harder to detect. This could be offset by using more pulses, but this

would shorten the maximum range again. So each radar uses a particular type of signal. Long

range radars tend to use long pulses with long delays between them, and short range radars

use smaller pulses with less time between them. This pattern of pulses and pauses is known

as the Pulse Repetition Frequency (or PRF), and is one of the main ways to characterize a

radar. As electronics have improved many radars now can change their PRF.

30

DIFFERENT TYPES OF RADARS

1. 3D Mobile Radar (PSM 33 Mk II)1. 3D Mobile Radar (PSM 33 Mk II)

3-D mobile radar employs monopulse technique for height estimation and using

electronic scanning for getting the desired radar coverage by managing the RF transmission

energy in elevation plane as per the operational requirements. It can be connected in air

defence radar network. The Radar is configured in three transport vehicles, viz., Antenna,

Transmitter cabin, Receiver and Processor Cabin. The radar has an autonomous display for

stand-alone operation.

FEATURES

Frequency agility  

Monopulse processing for height estimation  

Adaptive sensitivity time control  

Jamming analysis indication, pulse compression, plot filtering / tracking data

remoting 

Comprehensive BITE facility 

2. Low Flying Detection Radar (INDRA II)2. Low Flying Detection Radar (INDRA II)

The low-level radar 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

31

system consists mainly of an Antenna, Transmitter cabin and Display cabin mounted on three

separate vehicles.

SYSTEM CHARACTERISTICS

Range up to 90 km (for fighter aircraft) 

Height coverage 35m to 3000m subject to Radar horizon 

Probability of detection: 90% (Single scan) 

Probability of false alarm: 10E-6 

Track While Scan (TWS) for 2D tracking 

Capability to handle 200 tracks 

Association of primary and secondary targets 

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

Deployment time of about 60 minutes

FEATURES Fully coherent system  

Frequency agility  

Pulse compression  

Advanced signal processing using MTD and CFAR Techniques  

Track while scan for 2-D tracking  

Full tracking capabilities for maneuverings targets  

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

Integral IFF  

32

3. Tactical Control Radar3. Tactical Control Radar

This 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 minimizes mutual interference of tasks of both air defenders and

friendly air space users. This will result in an increased effectiveness of the combined combat

operations. 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.

FEATURES All weather day and night capability  

40 km ranges, 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  

Highly mobile system, to be used in all kinds of terrain, with short into and out of action

times (deployment/redeployment)

Clutter suppression  

33

RADAR APPLICATION

Air traffic control uses radar to track planes both on the ground and in the air, and

also to guide planes in for smooth landings.

Police use radar to detect the speed of passing motorists.

NASA uses radar to map the Earth and other planets, to track satellites and space

debris and to help with things like docking and maneuvering.

The military uses it to detect the enemy and to guide weapons.

34

RADAR RADAR TRANSMITTERTRANSMITTER

The radar transmitter produces the short duration high-power of pulses of energy that

are radiated into space by the antenna. The radar transmitter is required to have the following

technical and operating characteristics:

The transmitter must have the ability to generate the required mean RF power and the

required peak power

The transmitter must have a suitable RF bandwidth.

The transmitter must have a high RF stability to meet signal processing requirements

The transmitter must be easily modulated to meet waveform design requirements.

The transmitter must be efficient, reliable and easy to maintain and the life expectancy

and cost of the output device must be acceptable.

The radar transmitter is designed around the selected output device and most of the

transmitter chapter is devoted to describing output devices therefore:

Picture: transmitter of P-37

35

One main type of transmitters is the keyed-oscillator type. In this transmitter one

stage or tube, usually a magnetron, produces the rf pulse. The oscillator tube is keyed

by a high-power dc pulse of energy generated by a separate unit called the modulator.

This transmitting system is called POT (Power Oscillator Transmitter). Radar units

fitted with an POT are either non-coherent or pseudo-coherent. 

Power-Amplifier-Transmitters (PAT) are used in many recently developed radar sets.

In this system the transmitting pulse is caused with a small performance in a

waveform generator. It is taken to the necessary power with an amplifier flowingly

(Amplitron, klystron or Solid-State-Amplifier). Radar units fitted with an PAT are

fully coherent in the majority of cases.

o A special case of the PAT is the active antenna.

Even every antenna element

or every antenna-group is equipped with an own amplifier here.

Pictured is a keyed oscillator transmitter of the historically russian radar set P-37

(NATO-Designator: „Bar Lock”). The picture shows the typical transmitter system that uses

a magnetron oscillator and a waveguide transmission line. The magnetron at the middle of the

figure is connected to the waveguide by a coaxial connector. High-power magnetrons,

however, are usually coupled directly to the waveguide. Beside the magnetron with its

magnetes you can see the modulator with its thyratron. The impulse-transformer and the

pulse-forming network with the charging diode and the high-voltage transformer are in the

lower bay of this rack.

36

BRIEF DESCRIPTION OF THE RADAR SUBSYSTEM

Main Circuit of Radar Subsystem

High Tension Unit

Transmitter Unit

Lo+Afc Unit

Receiver Unit

Antenna

Video Processor

High Tension Unit -

The high tension unit converts the 115v 400Hz 3 Phase mains voltage into a d.c

supply voltage of about 4.2kv for the transmitter unit.

The exact value of the high voltage depends on the selected PRF(low,high or extra)to

Prevent the dissipation of the magnetron from becoming too high PRF the lower the supplied

high voltage

Transmitter Unit –

The transmitter unit Comprises

Submodulator

Modulator

Magnetron

Afc control Unit

The magnetron is a self – oscillating RF Power generator. It supplied by the

modulator with high voltage Pulses of about 20kvdc, whereupon it Produces X-band Pulses

with a duration of about 0.35us. The generated RF Pulses are applied to the receiver unit.

The Pulse repetition frequency of the magnetron pulses is determined by the

synchronizations circuit in the video Processor, Which applies start pulses to the sub

modulator of the transmitter unit. This sub modulator issues start Pulses of suitable amplitude

to trigger the thyraton in the modulator. Which is supplied by the high tension unit, Produces

high voltage Pulses of about 20kvDC.As a magnetron is self- oscillating some kind of

37

frequency control is required. The magnetron is provided with a tunning mechanism to adjust

the oscillating frequency b/w certain limits. This tunning mechanism is operated by an

electric motor being part of the Afc control circuit. Together with circuits in the Lo+Afc

units, a frequency control loop is created thus maintaining a frequency of the SSLO and the

magnetron output frequency.

LO+AFC Unit

The Lo+Afc unit determines the frequency of the transmitted radar pulses. It comprises-

Lock Pulses mixer

Afc discriminator

Solid state local oscillator(SSLO)

Coherent oscillator(COHO)

The Afc lock Pulses are Pulses are also applied to the COHO. The COHO outputs

signals with a freq. of 30Hz, and it is synchronized with the pulse of each transmitter Pulse.

In this way a phase reference signal is obtained, required by the Phase sensitive detector in

the receiver unit.

Receiver unit

The Rx unit converts the received RF echo signal to IF level and detects the IF signals

in two different ways, two receiver channel are obtained, called MTI channel and linear

channel.

The RF signal received by the radar antenna pass the circulator and are applied to a low

noise amplifier. The image rejection mixer mixes the amplified signals with the SSLO

signals, to obtain a 30MHz IF signal is split into two branches.viz, an MTI channel and a

linear channel.via directional coupler, a fraction of the low noise amplifier output is branch

offer and applied to the broadband jamming detector. The BJD is a wideband device, which

amplifies and detects the signal applied. The resulting signal is passed on the SJI-STC circuit

(Search jamming indication sensitivity time control) in the video Processor , if jamming

occurs, it is used to prevent a polar diagram of a jamming on the PPI Screen, Which shows

the direction of the jamming source.

In the MTI channel, the IP signal is amplified again by the MTI main amplifier and

applied to the phase sensitive detector. The second signal applied to the phase sensitive

38

detector PSD is the phase reference signal from the COHO. The output signal of the PSD

consists of video pulse, the amplitudes of which are a function of the phase difference

between the two input signal of the PSD. The polarity of the video pulse indicate whether the

phase difference is positive or negative.

The phase differences between the corlo signal and if echo signals from a fixed target

are constant whereas those between the COHO signal and if echo signals from a moving

target are subject to change.

The PSD output signal is applied to the canceller in the video processor.

The linear detector outputs positive video signals which are passed on to the colour

PPI drive unit.

Antenna

The antenna is a cosecant square parabolic reflector, rotating with a speed of about 48

r.p.m. in the focus of the reflector is a radiator, which emits the RF pulses from the circulartor

and which receives RF echo Pulses.

In the waveguide is Polarisation shifter, which causes the polarization of the RF

energy to the either horizontally or circularly. The polarization shifter is controlled by the

system operator.

Video Processor

The video processor processes the MTI receiver channel, to make the video suitable

for presentation on the colour PPI screen and for use by the video extractor.

The main circuit comprised by the video processor are :

Synchronization circuit.

Canceller

Floating level circuit

Correlator

Synchronization circuit

The synchronization circuit develops the start pulse for the sub modulator in the

transmitter unit, and accordingly it generates the timing pulses required by the canceller.

The repetition time of the start pulses depends on the PRF is staggered Pseudo-

randomly : 32 point stagger is used for low and high PRF and 64 point stagger is used for

39

extra PRF. The 64 point stagger for extra PRF is actually is compound of a 32 point staggered

short PRT and 32 point staggered long PRT and a 32 point staggered long PRT.

Canceller

The canceller is a circuit used to suppress the echo’s of fixed targets or very slow

moving targets. The canceller makes use of the difference in phase behavior moving and

fixed targets with moving target and phase differs from pulse to pulse, but with fixed targets

the phase is constant (i.e. the PSD output is constant). The suppression by the canceller is

limited. The higher the PRF of the radar pulses, the better the suppression factor; a further

cancellation improvement can be obtained by using a triple canceller instead of a double

canceller; here a compromise is to found.

40

SIGNAL PROCESSING UNIT

INTRODUCTION

The signal processing unit constitutes a very important functional block with vital

roles to perform in overall system configuration of receiver radar returns under normal

operating conditions are initially processed by the analogue processing stages (such as LNA,

IF, VIDEO DETECTOR etc.) and then processed by signal processor.

This type of signal processor is known as MOVING TARGET DETECTOR.

To improve the radar resolution in range, without the need for transmitting narrow

pulse, a technique called PULSE COMPRESSION is employed. This will avoid the need

for the transmission of a narrow pulse with high peak power, thus simplifying the transmitter

chain.

PRINCIPLE OF OPERATION

The signal processor consists of Digital Pulse Compression system followed by the

prewhitening clutter cancellation filter in the form of three pulses in MTI. The MTI output is

then processed by a sixteen point FFT processor with frequency domain windowing feature.

Final stage of data processing is detection. In detection block Cell Averaging (CACFAR)

with programmable threshold setting features in range/Doppler domain is used.

The MTI, FFT and CFAR are collectively known as MTD.

Similarly, in order to enable detection of tangentially moving (or low Doppler )

targets under noise limited, and weak to moderate ground clutter conditions, the Zero

Velocity Filter (ZVF) and its associated clutter map are used. PRF staggering scheme on

scan-to-scan and CPI-to-CPI basis is employed to ensure better performance against blind

speed conditions.

41

Signal Processor receives digital data from if processor. The data is received and

offset corrected (if AUTO OFFSET is ON SP control panel) and passed on to Digital Pulse

Compression (DPC) block.

The Digital Pulse Compression block carries out the matched filtering and correlation

of the returns with the transmitted phase codes. However, to enable the detection of weak

signals under noise and clutter backgrounds, and extraction of signal parameters such as

Doppler content, strength, range and azimuthal positions etc. further processing needs to be

carried out using clutter cancellation, filtering and integrations, and detection techniques.

Moving Target Detector (MTD) technique, facilitate optimal detection under

conditions of heavy clutter especially in Radars used for low looking surveillance role.

Keeping in view, the environment under which the INDRA-II is expected to perform its role

for the given specifications, the MTD technique naturally turns out to be the ideal choice of

its implementation.

Timing and control signals required by various functional blocks of the Signal

Processor and also the transmitter system are catered for as part of the Signal Processor

design feature. To facilitate the validation and testing of the signal processor, a swept

Doppler BITE is also provided. Similarly, to monitor on Oscilloscope outputs of MTI, FFT

and ZVF blocks, the necessary circuits in the form of D/A converters are also provided.

Interface circuits for MTD processed video on PPI as well for MTD data transfer to

centroid/RDP processor also form part of the design features.

HARDWARE ORGANISATION

The Signal Processor is realized on multiple, multilayer PCBs. The PCBs are grouped

into functions are packed into a single card cage. Each card cage is capable of housing up to

15 PCBs, along with a power supply module. The power supply takes ac input and caters for

the +5V, +15V and -15V supply needs of that card cage.

Two such card cages are put together in a card enclosure called Card Panel. Two

such card panels are being used to realize total signal processing hardware.

42

Each of the card panel is mounted on rails, to be able to pull out for maintenance

purpose.

FUNCTIONAL ORGANISATION

All the functions performed by Signal Processor can be organized under following

groups:

SIGNAL PROCESSING FUNCTIONS:

These are the main functions that process the radar echo, and hence form the main

functional chain.

DIGITAL PULSE COMPRESSION

AUTO OFFSET CORRECTION

MATCHED FILTER

MOVING TARGET INDICATOR

FFT PROCESSING

ZERO VELCITY FILTER (ZVF)

ADAPTIVE THRESHOLDING (CFAR)

INTERFACE FUNCTIONS:

These are the functions enabling the signal processor to communicate with other

units in the radar. Following are realized as dedicated interface on separate PCBs. Other

interfaces are part of their respective hardware.

DISPLAY INTERFACE

CENTROIDER INTERFACE

SYSTEM FUNCTIONS :

These functions receive controls (if any), and generate control for some functions

performed by other units of radar.

SYSTEM TIMING (also contain circuits for internal timing requirements of SP).

SYSTEM BITE – Generates control for simulated target generation by Receiver.

43

ADAPTIVE MSC (AMSC) – Adaptive map generation and transfer to receiver for

Adaptive Microwave Sensitive Control.

ECCM – Analyze and generate control for optimum frequency selection and jammer

indication on PPI.

MONITORING FUNCTIONS:

For parameter control and quick check on health of Signal Processor following

functions are performed:

RPM monitoring.

SP output monitoring.

Control Panel Function.

44

Fully Coherent RadarFully Coherent Radar

Figure 1: an easy block diagram of a fully coherent radar

The block diagram on the figure illustrates the principle of a fully coherent radar. The

fundamental feature is that all signals are derived at low level and the output device serves

only as an amplifier. All the signals are generated by one master timing source, usually a

synthesizer, which provides the optimum phase coherence for the whole system. The output

device would typically be a klystron, TWT or solid state. Fully coherent radars exhibit none

of the drawbacks of the pseudo-coherent radars, which we studied in the previous section.

Duplexer

The duplexer alternately switches the antenna between the transmitter and receiver so

that only one antenna need be used. This switching is necessary because the high-power

45

pulses of the transmitter would destroy the receiver if energy were allowed to enter the

receiver.

Mixer Stage

The function of the mixer stage is to convert the received rf energy to a lower,

intermediate frequency (IF) that is easier to amplify and manipulate electronically. The

intermediate frequency is usually 30 or 60 megahertz. It is obtained by heterodyning the

received signal with a local-oscillator signal in the mixer stage. The mixer stage converts the

received signal to the lower IF signal without distorting the data on the received signal.

IF-Amplifier

After conversion to the intermediate frequency, the signal is amplified in several IF-

amplifier stages. Most of the gain of the receiver is developed in the IF-amplifier stages. The

overall bandwidth of the receiver is often determined by the bandwidth of the IF-stages.

Power Amplifier

In this system the transmitting pulse is caused with a small performance in a

waveform generator. It is taken to the necessary power with a Power Amplifier flowingly.

The Power Amplifier would typically be a klystron, Travelling Wave Tube (TWT) or solid

state.

Stable Local Oscillator (StaLO)

The StaLO is also very stable CW RF oscillator, which generates the local RF

frequency simultaneously for up-conversion in the transmitter and down-conversion in the

receiver. Minimum FM noise (or phase noise) of the StaLO is an important characteristic.

This is because such noise would limit the overall MTI improvement factor, as fixed clutter

would inherit a Doppler component from the transmission. Similar arguments apply to FM

noise added by the output device.

Coherent Oscillator

The COHO is a very stable CW (Continuous Wave) oscillator locked to the IF

frequency (The COHO frequency is generally derived from a master crystal oscillator) and

constitutes the internal phase reference. The COHO provides the coherent reference signal to

46

the Phase Sensitive Detector and also through a frequency divider generates the system PRF

in the Synchronizer.

Mixer / Exciter

The function of this mixer stage is to convert the StaLO- Frequency and the COHO-

Frequency upwards into the phase-stabile continuous wave transmitter-frequency.

Waveform-Generator

The Waveform-Generator generates the transmitting pulse in low- power. It generates

the transmitting signal on an IF- frequency. It permits generating predefined waveforms by

driving the amplitudes and phase shifts of carried microwave signals. These signals may have

a complex structure for a pulse compression.

Phase Sensitive Detector

The IF-signal is passed to a phase sensitive detector which converts the signal to base

band, while faithfully retaining the full phase and quadrature information (I   &   Q- processing )

of the Doppler signal.

Signal Processor

The signal processor is that part of the system which separates targets from clutter on the

basis of Doppler content and amplitude characteristics.

Radarscope / Monitor

The indicator presents to the observer a continuous, easily understandable, graphic

picture of the position of radar targets. In recently radars the indicator would be a computer

display.

47

MAGNETRON

Figure 1: Magnetron МИ 29Г of the Radar „Bar Lock”

In 1921 Albert Wallace Hull invented the magnetron as a powerful microwawe tube.

Magnetrons function as self-excited microwave oscillators. Crossed electron and magnetic

fields are used in the magnetron to produce the high-power output required in radar

equipment. These multicavity devices may be used in radar transmitters as either pulsed or

cw oscillators at frequencies ranging from approximately 600 to 30,000 megahertz. The

relatively simple construction has the disadvantage, that the Magnetron usually can work

only on a constructively fixed frequency.

Physical construction of a magnetron

The magnetron is classed as a diode because it has no grid. The anode of a magnetron

is fabricated into a cylindrical solid copper block. The cathode and filament are at the center

of the tube and are supported by the filament leads. The filament leads are large and rigid

enough to keep the cathode and filament structure fixed in position. The cathode is indirectly

48

heated and is constructed of a high-emission material. The 8 up to 20 cylindrical holes around

its circumference are resonant cavities. The cavities control the output frequency. A narrow

slot runs from each cavity into the central portion of the tube dividing the inner structure into

as many segments as there are cavities.

Figure 2: Cutaway view of a magnetron

The open space between the plate and the cathode is called the interaction space. In

this space the electric and magnetic fields interact to exert force upon the electrons. The

magnetic field is usually provided by a strong, permanent magnet mounted around the

magnetron so that the magnetic field is parallel with the axis of the cathode.

Figure 3: forms of the plate of magnetrons

The form of the cavities varies, shown in the Figure 3. The output lead is usually a

probe or loop extending into one of the tuned cavities and coupled into a waveguide or

coaxial line.

a) slot- type

b) vane- type

c) rising sun- type

d) hole-and-slot- type

 

filament leads

cathode  pickup loop

49

Basic Magnetron Operation

As when all velocity-modulated tubes the electronic events at the production

microwave frequencies at a Magnetron can be subdivided into four phases too:

1. phase : Production and acceleration of an electron beam

2. phase : Velocity-modulation of the electron beam

3. phase : Forming of a „Space-Charge Wheel”

4. phase : Dispense energy to the ac field

Figure 4: the electron path under the influence of the varying magnetic field.

50

1. Phase: Production and acceleration of an electron beam

When no magnetic field exists, heating the cathode results in a uniform and direct

movement of the field from the cathode to the plate (the blue path in figure 4). The permanent

magnetic field bends the electron path. If the electron flow reaches the plate, so a large

amount of plate current is flowing. If the strength of the magnetic field is increased, the path

of the electron will have a sharper bend. Likewise, if the velocity of the electron increases,

the field around it increases and the path will bend more sharply. However, when the critical

field value is reached, as shown in the figure as a red path, the electrons are deflected away

from the plate and the plate current then drops quickly to a very small value. When the field

strength is made still greater, the plate current drops to zero.

When the magnetron is adjusted to the cutoff, or critical value of the plate current, and

the electrons just fail to reach the plate in their circular motion, it can produce oscillations at

microwave frequencies.

2. Phase: Velocity-modulation of the electron beam

The electric field in the magnetron oscillator is a product of ac and dc fields. The dc

field extends radially from adjacent anode segments to the cathode. The ac fields, extending

between adjacent segments, are shown at an instant of maximum magnitude of one

alternation of the rf oscillations occurring in the cavities.

Figure 5: The high-frequency electrical field

51

Well, the electrons which fly toward the anode segments loaded at the moment more

In the figure 5 is shown only the assumed high-frequency electrical ac field. This ac field

work in addition to the to the permanently available dc field.

The ac field of each individual cavity increases or decreases the dc field like shown in

the figurepositively are accelerated in addition. These get a higher tangential speed. On the

other hand the electrons which fly toward the segments loaded at the moment more

negatively are slow down. These get consequently a smaller tangential speed.

3. Phase: Forming of a „Space-Charge Wheel”

On reason the different speeds of the electron groups a velocity modulation appears therefore.

Figure 6: Rotating space-charge wheel in an eight-cavity magnetron

The cumulative action of many electrons returning to the cathode while others are

moving toward the anode forms a pattern resembling the moving spokes of a wheel known as

a „Space-Charge Wheel”, as indicated in figure 6. The space-charge wheel rotates about the

cathode at an angular velocity of 2 poles (anode segments) per cycle of the ac field. This

phase relationship enables the concentration of electrons to continuously deliver energy to

sustain the rf oscillations.

One of the spokes just is near an anode segment which is loaded a little more

negatively. The electrons are slowed down and pass her energy on to the ac field. This state

isn't static, because both the ac- field and the wire wheel permanently circulate. The

tangential speed of the electron spokes and the cycle speed of the wave must be brought in

agreement so. 

4. Phase: Dispense energy to the ac field

52

Figure 7: Path of an electron

Recall that an electron moving against an E field is accelerated by the field and takes energy

from the field. Also, an electron dispense energy to a field and slows down if it is moving in

the same direction as the field (positive to negative). The electron spends energy to each

cavity as it passes and eventually reaches the anode when its energy is expended. Thus, the

electron has helped sustain oscillations because it has taken energy from the dc field and

given it to the ac field. This electron describes the path shown in figure 7 over a longer time

period looked. By the multiple breaking of the electron the energy of the electron is used

optimally. The effectiveness reaches values up to 80%.

Figure 13: Magnetron M5114B of the ATC-radar ASR-910

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Figure 13: Magnetron VMX1090 of the ATC-radar PAR-80 This magnetron is even equipped with the permanent magnets necessary for the work.

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CONCLUSION

Making this project was a huge learning experience for us. We have enjoyed building the project brick by brick, and it has given us the opportunity to come up with new innovative ideas and show talent. The Project was our first step into practicality of theory on large scale and an introduction into Industry and concept of Radar and Transmitter . It created very challenging situations for us, which involved a lot of mind boggling. As we are not professionals we built this project according to our knowledge and skills, we tried our level best to make it as good as we can, but still it has a lot of scope of improvement. But its overall look and feel great and gives an exposure of Indutry and Professionalism .

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