Bel Project & Training Report

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BHARAT ELECTRONICS LIMITED

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.

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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.

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 GTBKIET.Six Months Training 2

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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

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.


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CORPORATE MOTTO , MISSION AND OBJECTIVES:

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. P.C.B. Fabrication

3. Quality Control Works-Radar

4. Work Assembly- Communication

5. Magnetics

6. 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


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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

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.


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A --- Physical and Mechanical defects.

B --- Wrong Writing

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.

P.C.B. FABRICATION

P.C.B. stands for Printed Circuits Board. It’s an integral part of the Electronics

equipment as well as all the components are mounted on it. It consists of the fiberglass sheet

having a layer of copper on both sides.

TYPES OF PCBs

Single Sided Board : Circuits on one side.

Double Sided Board : Circuit on Both side.

Muti-layer Board : Several layers are interconnected through hole metallization.

Raw material for PCB ’s

Most common raw material used for manufacturing of PCBs is copper cladded glass

epoxy resin sheet. The thickness of the sheet may vary as 1.2, 2.4 and 3.2mm and the

standard size of the board is 610mm to 675mm.


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Operation in process

Following steps are there for PCB manufacturing:-

CNC Drilling

Drill Location

Through Hole Plating

Clean Scrub and Laminate

Photo Print

Develop

Cu electroplate

Tin electroplate

Strip

Etching and cleaning

Tin Stripping

Gold plating

Liquid Photo Imageable Solder Masking (LPISM)

Photo print

Develop

Thermal Baking

Hot Air leaving

Non Plated Hole Drilling

Reverse Marking

Sharing & Routing

Debarring & Packing

P.C.B. is a non-conducting board on which a conductive board is made. The base

material, which is used for PCB plate are Glass Epoxy, Bakelite and Teflon etc.

Procedure for through hole metallization

Loading-Cleaner-Water Rinse-Spray Water-Rinse-Mild Etch-Spray Water-Rinse-

Hydrochloric Acid-Actuator-Water Rinse-Spray Water-Rinse-Accelerator Dip-Spray Water-

Rinse- Electrolyses Copper-Plating-Plating- Spray water-Rinse-Anti Tarnish Dip-Hot Air

Drying- Unloading.


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After through hole metallization, photo tool generation is done which is followed by

photo printing. In this the PCB is kept b/w two blue sheets and the ckt. is printed on it. A

negative and a positive of a ckt. are developed. To identify b/w the negative and positive,

following observation is done. If the ckt. is black and the rest of the sheet is white, it is

positive otherwise negative.

Next, pattern plating is done. The procedure for pattern plating follows:

Loading- Cleaner- Water rings- Mild etch- Spray- Water Rinse-Electrolytic- Copper

plating- Water rinse- Sulfuric acid-Tin plating- Water rinse- Antitarnic dip- Hot air dry-

Unloading. To give strength to the wires so that they can not break. This is done before

molding. Varnishing is done as anti fungus prevention for against environmental hazard.

After completion of manufacturing proceeds it is sent for testing. This is followed by

resist striping and copper etching. The unwanted copper i.e. off the tracks is etched by any of

the following chemicals. After this, tin is stripped out from the tracks.

After this solder marking is done. Solder marking is done to mark the tracks to get

oxidized & finally etch. To prevent the copper from getting etched & making the whole

circuit functionally done.

There are three types of solder marking done in BEL :

Wet solder mask: Due to some demerits this method is totally ruled out. The demerit was

non- alignment, which was due to wrong method applied or wrong machine.

Dry pin solder mask : Due to wastage of films about 30% this method is also not used now.

Liquid photo imaginable solder mask (LPISM): In this first presoaking is at 80 degree

Celsius for 10 to 20 minutes. Next, screen preparation is done. The board is covered by a silk

cloth whose mesh is T-48. The angle to tilt of the board is 15 degree to 22.5 degree.


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The next is ink preparation:

Ink + Hardener

71 %: 29 %

(150 gms.) : (300gms.)

+

Butyrate solo solve 50gms/kg.

Ink preparation-

It uses:-

Ink-----100gm

Catalyst----10% of total weight

Reducer-----10% of total weight

The catalyst is used as binder and prevents the following, while reducer is used as thinner.

The three things are then fully mixed.

For wash out, following procedure takes place.

Water-Lactic acid-Water-Bleaching power-Water-caustic Soda-Water-Air dry-TCE.

After wash out, final baking for one hour at the temp. Of 20degree C is done. After this

shearing or routing is done which is followed by debarring and packing.


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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.


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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

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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MAGNETICS

In this department different types of transformers and coils are manufactured ,

which are used in the various Defence equipments i.e. radar , communication

equipments.

This department basically consists of three sections :

1.) PRODUCTION CONTROL :- Basic function of production control is to plan the

production of transformer and coils as per the requirement of respective division

(Radar and Communication). This department divided into two groups :

(a) Planning and (b) Planning store .

2.) WORKS (PRODUCTION) :- Production of transformers and coils are being

carried out by the works departments.

3.) QUALITY CONTROL :- After manufacturing the transformer/coils the item is

offered to the inspection department to check the electrical parameters(DCR , No load

current , full load current , dielectric strength , inductance , insulation resistance and

mechanical dimension as mentioned in the GA drawing of the product.

The D&E department provides all the information about manufacturing a coil and the

transformer.

The various types of transformers are as follows :

1. Air cored transformers

2. Oil filled transformers

3. Moulding type transformers

4. P.C.B Mounting transformers :-

(a) Impedance matching transformers

(b) RF transformers

(c) IF transformers


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The various types of cores are as follows :

1. E type

2. C type

3. Lamination

4. Ferrite core

5. Toroidal core

Steps involved in the process of manufacturing of transformer/coils:

Preparation of former : Former is made of plastic bakelite comprising a male

and female plates assembled and glued alternately to form a hollow rectangular

box on which winding is done.

Winding : It is done with different material and thickness of wire. The

winding has specified number of layers with each layer’s having a specified

number of turns. The distance between the two turns should be maintained

constantly that is there should be no overlapping. The plasatic layer is inserted

between two consecutive layers.

The various types of windings are as follows :

Layer Winding

Wave Winding

Bank Winding

Insulation : For inter-winding and inter layer , various types of insulation sheets

viz. Craft paper , paper , leather , oil paper , polyester film are being used.

Protection : To protect the transformer from the external hazards , moisture ,

dust and to provide high insulation resistance , they are impregnated.


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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


http://en.wikipedia.org/wiki/Visible_light

http://en.wikipedia.org/wiki/Sound

http://en.wikipedia.org/wiki/Doppler_Effect

http://en.wikipedia.org/wiki/Rain

http://en.wikipedia.org/wiki/Ship

http://en.wikipedia.org/wiki/Aircraft

http://en.wikipedia.org/wiki/Radio

http://en.wikipedia.org/wiki/Acronym_and_initialism

http://www.windows.ucar.edu/tour/link=/earth/Atmosphere/tornado/radar.html

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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.


http://en.wikipedia.org/wiki/Tungsram

http://en.wikipedia.org/wiki/Zolt%C3%A1n_Bay

http://en.wikipedia.org/w/index.php?title=Christian_H%C3%BClsmeyer&action=edit

http://en.wikipedia.org/wiki/History_of_radar

http://en.wikipedia.org/wiki/Engineer

http://en.wikipedia.org/wiki/Scientist

http://en.wikipedia.org/wiki/Inventor

http://en.wikipedia.org/wiki/Traffic

http://en.wikipedia.org/wiki/Speeding

http://en.wikipedia.org/wiki/Police

http://en.wikipedia.org/wiki/Air_traffic_control

http://en.wikipedia.org/wiki/Precipitation_(meteorology)

http://en.wikipedia.org/wiki/Meteorology

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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


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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...


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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


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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.

IFF UNIT

IFF is basically a radar bacon system employed for the purpose of general

identification of military targets .The bacon system when used for the control of civil air

traffic is called as SECONDARY SURVEILLANCE RADAR (SSR).

Primary radar locates an object by transmitting signal and detecting the

reflected echo. A secondary radar system is basically very similar to primary radar

system except that the returned signal is radiated from the transmitter on board the

target rather then by reflection, i.e. it operates with a cooperative ‘active’ target while

the primary radar operates with “passive target’.

Secondary radar system consists of an interrogative and a transponder. The

interrogator transmitter in the ground station interrogates transponder equipped aircraft,

providing two way data communication on different transmitter and receiver frequency .The

transponder on board the aircraft on receipt of a chain of pulses from ground interrogator,

automatically transmit the reply, coded for the purpose of identification, is received back to

the ground interrogator where it is decoded and displayed on a radar type presentation.

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


http://en.wikipedia.org/wiki/Radar_cross_section

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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.

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


http://en.wikipedia.org/wiki/Pathloss

http://en.wikipedia.org/wiki/Multipath

http://en.wikipedia.org/wiki/Vacuum

http://en.wikipedia.org/wiki/Image:Sonar_Principle_EN.svg

http://en.wikipedia.org/wiki/Image:Sonar_Principle_EN.svg

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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.

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.


http://en.wikipedia.org/wiki/PRF

http://en.wikipedia.org/wiki/Pulse_Repetition_Frequency

http://en.wikipedia.org/wiki/Signal_(information_theory)

http://en.wikipedia.org/wiki/Energy

http://en.wikipedia.org/wiki/Distance

http://en.wikipedia.org/wiki/Speed_of_light

http://en.wikipedia.org/wiki/Speed_of_light

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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

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

separate vehicles.


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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

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


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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


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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.


http://electronics.howstuffworks.com/satellite.htm

http://electronics.howstuffworks.com/airplane.htm

http://electronics.howstuffworks.com/air-traffic-control.htm

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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


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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.


http://www.radartutorial.eu/08.transmitters/tx07.en.html


http://www.radartutorial.eu/06.antennas/an15.en.html







http://www.radartutorial.eu/01.basics/rb05.en.html



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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


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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


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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


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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.

The operation of the canceller depends on the selected PRF :

Low and high PRF ;

The canceller is swithched as double canceller.

Extra PRF :

The PRF jumps from pulse to pulse between low PRF and high PRF.

The canceller switched to double is a digital three pulse comparison canceller.

Video’s are :

Undelayed video (V0)

Video delayed by one PRT (V1)

Video delayed by two PRT’s (V2)

By addition, multiplication and subtraction these video are combined to obtained a

canceller output according to the following formula.

V out (double) = 2 V1 – (V 0 + V 2)

The canceller switched to triple is digital four pulse comparison canceller.

This circuit the following video’s are obtained :

Undelayed Video (V0)

Video delayed by one PRT (V1)

Video delayed by two PRT (V2)

Video delayed by three PRT’s (V3)

Canceller output according to the following formula :

V out (triple) = V0 – 3 V1 + 3 V2 – V3


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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.


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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.


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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.


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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.

FUNCTIONAL DESCRIPTION

The following are detailed description of each functional block.

DIGITAL PULSE COMPRESSION (DPC) BLOCK

DPC card module performs the following functions:

I/Q channel Digital Matched Filtering.

Automatic DC offset correction for I/Q ADC data.

Adaptive Microwave Sensitivity Control.

Online JAM sensing with real – time ECCM controls.

Systems BITE control for generation of simulated targets for on-line injection at RF & IF

levels.

PD /Pfa / Antenna RPM monitoring & Indication.

The Digital Card Module houses 13 nos. of extended double Euro Multi-layer PCBs

as part of the Signal Processing Rack of INDRA-PC RADAR.

This card module receives the INPHASE and QUADRATURE channel ADC data

(12+12 bits) from the 30 MHz IF processor. Automatic DC offset correction is applied to this

data and inputted to the digital matched filter. The I & Q channel pulse compressed signal is

then fed to the corner turning memory of the MTD processor in the next card module. The


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received ADC data also goes after buffering to the Adaptive Microwave Sensitivity Control

(AMSC) card and ECCM control card.


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MATCHED FILTER FUNCTION BLOCK

DPC CONTROL CARD # 1, DPC CONTROL CARD # 2, I-CH matched filter and

Q-CH matched filter together constitutes the matched filter block.

I/Q ADC data from IF unit, offset corrected in Auto Offset Correction Card enters

DPC CNTL CARD # 1.Here I/Q ADC data is added to I/Q clutter BITE (CLUT). The clutter

BITE is initiated with the help of CLUT PULSE trigger when needed only.

I/Q ADC + CLUT data is multiplexed with I/Q SIM data and the selected data goes to

I/Q matched filters. SIM data is used for on-line diagnostics and fault indication.

Under normal operating conditions, ADC data is present during radar operational

range and DPC SIM data is injected during the dead range of the radar. There is an over-

riding switch control DPC BITE ON/OFF by which only DPC SIM data can be selected as

input to I/Q matched filters for diagnostics purposes.

I and Q matched filters look for the correlation in the code between the transmitted

pulse and that of received echo pulse. The peaking of the signal occurs whenever the

correlation exists. There are two banks in the matched filter performing the similar filtering

operation and the selection of a particular bank for operation is decided by the signature

analysis circuit in DPC CNTL CARD # 2.

Signature analysis is carried out on-line during the dead range. The matched filter

output patterns for I & Q DPC SIM data are stored in EPROMs. A signature analysis gate is

opened during which the on-line matched filter outputs are compared with the signatures

stored and the error condition if any is detected

With BANK # 1 selected, I-DPC data is selected for signature analysis for 8 sweeps

and then Q-DPC data for the next 8 sweeps. The same sequence is followed when BANK # 2

is selected. If there is any error in BANK # 1 or BANK # 2 of I-MF or BANK # 1 or BANK

# 2 of Q-MF, an appropriate LED is switched on. The signature analysis logic automatically

switches to alternate bank when one bank is found faulty.


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The codes used in operation are stored in a PROM band can be selected manually

using DIP-switch on the card or automatically when code agility mode is selected.

DPC CONTROL CARD # 1 generates the various control signals for signature

analysis.

Code generation and distribution to the other subunits/subsystems, is done, in DPC

CONTROL CARD # 2. This card also receives various signals and distributes them.

DPC output analog video is generated for monitoring purposes in DPC CONTROL

CARD # 1 & # 2.

AUTO OFFSET CORRECTION FUNCTION Auto offset correction block comprises –

Auto offset correction hardware card, and

AMSC- Master Card.

The estimation of offset value in I/Q ADC data is done on-line every scan using

ADSP processor in AMSC-Master Card. This offset data is subtracted (with proper sign)

from the real time I/Q data for every range cell in following scan.

During the dead CPI period, when there is no transmission, I/Q samples are taken at

3microsec. interval over several range cells. This way samples are collected over several dead

CPIs in a scan. The mean of these samples is computed to get the offset value in each of the

channels. These I/Q offset values are passed on to the Auto Offset Correction Card, where the

hardware corrects the offset in the two channels on-line in the following scan.

Auto Offset Correction Card receives I-ADC and Q-ADC data from IF processor unit

corrects the offset in the two channels and passes on to DPC CONTROL CARD # 1. It also

buffers and distributes the I-ADC and Q-ADC data to AMSC and ECCM CARD #1.

BULK MEMORY FUNCTION BLOCK

As the processing requirement is in the batch mode for MTD, the radar real time data

has to be reordered and to processing block. This reordering is done in the bulk memory. This


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circuit consists of two PCBs. The first PCB is the Bulk Memory Control Card. In this PCB,

the address generations for both read and write operations; control generation and BITE

generation are implemented. In the second card mainly the memory and the corresponding

switching buffer is available. The memory in the second board is organized in such a way

that while DPC output data is written in one of the memories called bank ‘A’, the other

memory called bank ‘B’, outputs the previous CPI data for processing block. The clock used

for the read operation is gated Rck, generated in system timing card. The bank switching is

done after every CPI.

MOVING TARGET DETECTOR PROCESSOR BLOCK

MTD is an example of an MTI processing system that takes the advantage of the

various capabilities offered by digital techniques to produce improved detection of moving

targets.

Infact,

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

MOVING TARGET INDICATOR FUNCTION BLOCK

It is possible to remove from the radar display the majority of clutter, that is, echoes

corresponding to stationary targets, showing only the moving targets. This is often required,

although of course not in such applications as radar used in mapping or navigational

applications. One of the methods of eliminating clutter is the use of MTI, which employs the

DOPPLER EFFECT in its operation.

DOPPLER EFFECT

The apparent frequency of electromagnetic sound waves depends on the relative

radial motion of the source and the observer. “If source and observer are moving away from

each other, the apparent frequency will decrease, while if they are moving towards each

other, the apparent frequency will increase.

The Doppler effect is observed only for radial motion, not for tangential motion. Thus

no Doppler effect will be noticed if a target moves across the field of view of radar.


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A Doppler shift will be apparent if the target is rotating, and the resolution of the

radar is sufficient to distinguish leading edge from its trailing edge.

FUNDAMENTALS OF MTI

Basically, the moving-target indicator system compares a set of received echoes with

those received during the previous sweep. Those echoes whose phase has remained constant

are then cancelled out. This applies to echoes due to stationary objects, but those due to

moving targets do show a phase change; they are thus not cancelled-nor is noise, for obvious

reasons.

The fact that the clutter due to stationary targets is removed makes it easier to

determine which targets are moving and reduces the time taken by an operator to ‘take in’ the

display.

It also allows the detection of moving targets whose echoes are hundreds of times

smaller than those of nearby stationary targets and which would otherwise have been

completely masked.

The phase difference between the transmitted and received signals will be constant for

fixed targets, whereas it will vary for moving target.

The advantage offered by digital MTI processing:

Compensation for “blind phases”, which cause a loss due to the difference in phase

between the echo signal and the MTI reference signal. This is achieved by use of I & Q

processing, something that was always known to be of value for MTI processing, but

which was not convenient to implement with analog methods.

Greater dynamic range can be obtained than was possible with acoustic delay lines.

Digital processor can be made reprogrammable.

Digital MTI is more stable and reliable than analog MTI, and requires less adjustments

during operation in the field.


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FFT PROCESSOR FUNCTION BLOCK

FAST FOURIER TRANSFORM (FFT)

Digital filtering involves the use of Fourier transform. The FFT requires less

computational effort, and it has been popular for many applications. It has some limitations,

however compared to. The number of samples has to be expressed as 2n if a filter bank is

being generated, all filters have identical responses, they will be uniformly spaced

frequencies, and the weighting coefficients are not optimum since they cannot be chosen

independently for each filter. The filters possible with a non-FFT filter bank also can achieve

greater attenuation of moving clutter (such as rain or chaff) because of the greater flexibility

available in their design. There are times, therefore, when the classical Fourier transform may

be more advantageous than the FFT even though the FFT might be quicker and require less

complexity.

HARDWARE

FFT processor has been realized on 12 multilayer PCBs. The PCBs are as follows:

FFT Timing and Control

Cascade Buffer for FFT

Processor 1 ALE

Processor 1 Feedback

Processor 1 Feed forward

Complex multiplier

Processor 2 ALE (Architecture same as Processor 1 ALE)

Processor 2 Feedback (Architecture same as Processor 1 Feedback)

Processor 2 Feed forward (Architecture same as Processor 1 Feed forward)

Frequency Domain Window (Real)

Frequency Domain Window (Imag.)

Magnituder


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ZERO VELOCITY FILTER FUNCTION

The MTD also uses a new concept of Zero Velocity filter (ZVF) to overcome the

probability of missing the targets which have a velocity falling in the zero Doppler zone. This

will be the case of targets which are flying tangential radar and low velocity radial targets,

who’s Doppler is such hat they fall in zeroeth filter. Also since the response of the DMTI is

rather poor for low Doppler targets, there is every chance that these targets may go under.

ZVF performs its function by forming a clutter map.

Clutter map: A conventional MTI processor eliminates stationary clutter, but it also

eliminates aircraft moving on a crossing trajectory (one perpendicular to the radar line of

sight) which causes the aircraft’s radial velocity to be zero. This is unfortunate since the radar

cross-section of an aircraft is relatively large when viewed at the broadside aspect presented

by a crossing trajectory. The MTD took advantage of this large cross-section to detect the

targets that normally would be lost to a simple MTI radar. It did this with the aid of a clutter

map that stored the magnitude of the clutter echoes in a digital memory. The clutter map

established the thresholds used for detecting those aircraft targets which produce zero radial

velocity.

There may be many range cells which may not contain clutter, or contain low clutter,

but due to the poor response of MTI. These may be the implementation of the ZVF will allow

the detection of targets whose return exceeds that of the clutter in that particular range –

azimuth cell. The ZVF is implemented by integrating all the 18 returns of a CPI, and whose

response extends to the frequency band covered by the zeroeth filter.

In the zeroeth Doppler cell, the clutter is generally due to the ground echoes. To

estimate the average backscatter signal level, the entire range – azimuth space is divided into

fine grain resolution cells and the returns are stored in the form of a map. To build up the map

accurately, each antenna resolution is broken into 256 CPIs and there are 2560 range cells.

The ZVF is made up of magnitude of 18 samples, which are formed by first adding 9 samples

and then adding the next 9 samples coherently and non-coherently adding up the sums.


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CFAR PROCESSOR BLOCK

CFAR is used in radars to maintain effectiveness when there are too many extraneous

crossings of a fixed threshold caused by clutter or noise. Automatic tracking of targets can be

seriously degraded if excessive false alarms occur.

CONSTANT FALSE ALARM RATE (CFAR) processor block is one of the major

functional blocks of digital signal processor. The output of the FFT filtering block is further

processed to facilitate the following

Generation of adaptive threshold levels using Moving Window concept.

Detection of signals and extraction of primitive (primary) data information pertaining to

the detected signals.

The output of the FFT magnituder forms the main data input to the CFAR Processor

block. Functional sub-blocks such as the running sum computation, Pipeline memory storage,

Mode Selection Multiplier and threshold detection constitute the hardware blocks of the

CFAR processor. In the CFAR processor block, the threshold levels are so found, so as to

enable the detection of the signals with the constant false alarm rate under conditions of

mainly thermal noise and also under jamming and interference backgrounds. In order to

achieve this Newman Person detection criterion, with adaptive thresholding in all the Doppler

channels using moving window concepts is implemented.

In case of Non-Gaussian clutter dominated Doppler channels designed features have

been provided to selectively apply higher threshold levels, so as to restrict the false alarm to

the acceptable level.

The CFAR Processor block functions with its own timing and control signals. The

master source for these timings however is from the system timing circuit. CFAR BITE

facility has also been provided to test and validate the CFAR processor block in stand-alone

mode.


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DISPLAY VIDEO INTERFACE FUNCTION

This function is to generate trigger and videos for two Display consoles.

The raw video from IF processor is mixed with Jammer video and is then buffered to

generate RAW video for Display Consoles.

Mixing CFAR output with Jammer video and AMSC video generates the MTD video

for Display Consoles.

The triggers are suitably delayed Radar Trigger (RT), they are also buffered before

sending to Display Consoles.

CENTROID INTERFACE FUNCTION

The data packet to be sent to the centroider from CFAR Processor, basically, contains

the information such as signal strength, Doppler bin number (velocity bin), Range cell

number, CPI number, PRF code and data pertaining Jam to strobe, Tx blanking flag, carrier

frequency code, etc.

This data packet needs to be tagged to the threshold crossing pulse to facilitate

centroiding and subsequent data processing. The Threshold Crossing decision on sample-to-

sample basis is carried out at real time processing rate of 250ns per report. However the

centroider accepts the information asynchronously. This necessitates the use of hardware

buffering devices such as FIFOs. The information needs to be passed to a 16-bit data bus.

Hence various sets of information indicated above need to be generated, edited, formatted

and sequenced before data-transfer.

The required hardware design was carried out in two PCBs. The first PCB consists of

timing and control circuits and a part of data editing. The next PCB consists of sequencing,

FIFO store and data interface.

SYSTEM TIMING FUNCTION


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This is the function that generates all the basic timing signals required for use within the

Signal Processor as well as other units of the radar. It generates necessary synchronization

signals for Transmitter and Sampling clock for IF Processor. The signals thus generated are

described below.

20 MHz GENERATOR

20 KHz GENERATOR

PRF GENERATOR

CPI PAIR GATE

NM AND ACP GENERATION

BITE FUNCTION BLOCK

The interactive BITE sub-system provides comprehensive test facilities. Two target

pulses can be generated using commands from a keyboard. The commands have been chosen

in a way that it is easy to remember and consists of two alphabets followed by suitable

functional parameters.

The following are the BITE controls that can be used for signal processing and RDP

checks.

BITE pulses can be positioned in any range (distance – wise or range cell – wise) and in

any azimuth.

BITE pulses can be moved along range and / or along azimuth at any speed (0 to 9999

Kms per Hr).

Any Doppler shift (0 to 100 %) in terms of percentage of PRF can be given.

Target straddling can be introduced.

Asynchronous interference can be introduced along with BITE pulse.

BITE pulse can be fed at RF of IF stages.

Primary and secondary BITE pulses can be switched on/off individually.

BITE pulses can be introduced continuously (in a ring mode) or once a scan.


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Multiple BITE pulses can be generated for each of the primary target pulses along range

as well as along azimuth. A maximum of 16 pulses can be generated along range and 32

along azimuth. Also, the separation between these multiple pulses can be varied in

multiples of 1.8 Km along range and in multiples of 7.5 degree along azimuth.

Apart from these, BITE subsystems can be used to generate programmable ECCM sector

controls. They are

To selectively blank radar transmission in a sector (up to 8 such sectors).

To selectively effect data blanking for centroids in any sector (up to 8 such sectors).

To selectively choose random frequency or Least Jammed Frequency operating in

any sector (up to 8 such sectors).

The BITE subsystem is distributed in three PCBs. BITE control card #1 contains

BITE Processor.

Keyboard interface.

Boot memory and data memory PROMs.

Clock generation circuitry.

Decoders for various registers.

Sector control registers.

Circuit for generating scan interrupts.

Apart from these serial interface circuits and spare input registers and output registers

have been provided.

BITE Control Card # 2 is identical for target _ 1 and target – 2. This card consists of:

Range registers.

Azimuth registers.

Circuit for Doppler control.

Circuit for antenna modulation.

Circuit for multiple target pulse generation along range and azimuth.


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Circuit for pulse width control along range and azimuth.

Decoders for various registers.

AMSC FUNCTION BLOCK

Transportable and mobile tactical radar systems which need to operate with coverage

extending over hilly and mountainous terrain have to cope with heavy volumetric clutter even

at distant ranges. Under such conditions STC circuit which is widely used to reduce large

echoes from close-in clutter will not be effective.

**Hence an adaptive microwave sensitivity control is employed which has the

capability to intelligently self-program the receiver sensitivity in each range–azimuth cell in

an accurately and optimum fashion.

This is done by deriving a coarse clutter map from a zero-velocity (low-pass) filter,

built up over a few scans for each range-azimuth cell, operating on the I & Q channel ADC

data. The clutter map is built after applying a constant attenuation of 30dB uniformly in the

total range-azimuth plane. Then the relative clutter level w.r.t. the saturation point is

computed for each range-azimuth bin and the corresponding attenuation accurately worked

out to bring the clutter everywhere into the linear dynamic range. The adaptive attenuation

programming is a one time operation initiated under full power transmission by the radar

operator with the push of a button. This may be done whenever the radar site is changed or

whenever required.

AMSC block is configured as AMSC-MASTER & AMSC-SLAVE. AMSC-

MASTER is housed in SPU-Rack & AMSC-SLAVE housed in Receiver-Rack. The two are

connected through the serial line.

The function of AMSC-MASTER is to derive the clutter map built up over 8 scans

from I & Q ADC data and to transfer this map data to AMSC-SLAVE processor through a

serial channel.

AMSC-SLAVE receives the map data, stores in its memory as a replica of map

memory of MASTER, transfers the map data from RAM to the EEPROM and starts


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outputting map values every PRT to RF CONTROL card for generating attenuation values.

The derivation of coarse clutter map from zero-velocity filter is done as follows. In

every CPI 210 range samples of I & Q data are taken starting with every PRT.

The range samples are taken at 3 sec interval. The I & Q samples for each range cell

are integrated over 16 PRTs in a CPI. The magnitude of I & Q data is computed for each

range cell using 7/8 L + 1/2 S algorithm and stored in external memory. This way magnitude

for all the range azimuth cells in a scan is computed and stored in a memory. The

computation and accumulation of magnitude is done for over 8 scans and the action is

stopped. Since we have256 CPIs in a scan and 200 range cells per CPI, the number of range

azimuth cells per scan will be 256 * 200 =51,200 i.e., 51K of external memory is required

for storing the map information.

External RAM used in the circuit is of 128K words capacity and 8 pages are used to

store the map information. The processor selects the memory page using the MSB 3 bits of

CPI number. The locations in each page are addressed by the processor using LSB 5 bits of

CPI number and 8 bits of range cell address.

The data is send to AMSC-SLAVE on a serial port of the processor. The MASTER-

to-SLAVE communication is synchronous (same serial clock is used for both the processors).

Mode of communication is duplex mode, where in the word sent by MASTER is echoed back

by SLAVE. The MASTER processor checks for the correctness of the received word before

sending the next word. If there is any error, the word is repeated. The AMSC block operates

in three modes.

MODE # 1: No clutter map generation and no transfer of data in this mode the slave

has to only output the map values stored in RAM every PRT. This is normal mode of

operation.

MODE # 2: No clutter map generation, only data stored in AMSC-MASTER

EEPROM is transferred to AMSC-SLAVE.

MODE # 3: Clutter map generation and transfer of data to SLAVE by MASTER.

Slave processor has to receive the data and store in its external memory. Once the data GTBKIET.Six Months Training 57

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transfer is completed, the data is outputted with every PRT.

For each word of data to be transferred, three 16-bit words are sent to slave. First

word gives the page number of the memory, second word gives the address of the memory

where data has to be stored and the third word is the data which has to be stored in the

address location given by the second word. The MSB three bits of each word are used to code

the word as page number, address and data. The slave has to decode the three bits and take

appropriate action like selecting memory page number or forming address pointer to load the

data or load the data into specific location of the memory.

The process of derivation of clutter map has to be done with full transmitter power

ON and a 30dB uniform attenuation applied to the front end, which is done by the slave

processor.

AMSC action is initiated by AMSC-INIT switch on the display front panel. AMSC-

INIT switch resets both MASTER and SLAVE processors. If AMSC-INIT switch is held

pressed for one scan, MASTER processor should go in for derivation of clutter map.

If this facility is not given, any accidental pressing of the switch during Radar

operation causes 30dB front end attenuation being applied by the SLAVE processor and the

detection will suffer for 8 scans.

The hardware in AMSC card senses whether the AMSC-INIT switch is pressed for

one scan and set a flag.

After initialization with reset, the MASTER processor waits for one scan time and

polls the flag. If the flag is active, it starts with MODE # 3. If not it will go to MODE # 2.

Sampling of data for map generation starts with the first CPI encountered after

initialization with reset. This first CPI number read from counter is stored. The functions of

processor in each CPI are:

Read the CPI number.

Read current I/Q values of each range cells ; accumulate will previous I/Q values

stored in internal memory.GTBKIET.Six Months Training 58

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Compute the magnitude of accumulated I and Q values of previous CPI.

ECCM CONTROL FUNCTION BLOCK

In every pulse repetition time [PRT] interval during the dead range (beyond 94 Kms),

the receiver is switched through all the 11 frequencies, in two batches and A/D, I-Q samples

corresponding to these frequencies is collected. This is repeated for a total of 15 PRTs in

every coherent pulse interval (CPI). Hence in all 660 samples of ADC data (or 330 complex

I/Q samples) are colleted and stored in the internal data memory of the processor. An MTI

operation is done on this data and then magnituding and hence the magnitude for each

frequency is found out. The MTI operation is done to cancel noise due to clutter if any,

occurring in the dead range corresponding to the Transmitted frequency thus avoiding

erroneous estimation of least jam frequency. The magnitudes obtained for each of the

frequencies in a CPI is obtained as well as sum of all the magnitudes. The magnituded data

is used for analyzing and to compute the different functions to be performed by this processor

and outputted. These different functions are described below:

LEAST JAMMED FREQUENCY

The magnitudes obtained for each frequency are compared and the frequency

corresponding to minimum magnitude gives the LJF. This is done in every CPI. Also the

magnitude corresponding to the present CPI-LJF, is compared with that of the previous

CPI-LJF and if it is less than 5 times that of previous one, only then the current LJF is put-

out, else the previous LJF itself is output as the LJF for the next CPI.

AUTO THRESHOLD BITS

3 Bits are generated by comparing the magnitude for the LJF in a CPI with some

constant value of expected jamming noise and after weighting, are sent out to the CFAR

processor. This is done in every CPI. 2 bits of data are generated to indicate the jam level

corresponding to the LJF and sent to frequency indication panel unit on display console.

AUTO ATTENUATION CONTROL


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Once again depending upon the value of the sum of magnitudes, like auto LJF, auto

STC off and also 24 dB dead range RF attenuation ON are generated and sent to appropriate

units.

JAM STROBE PRESENTATION

Using the sum of all the magnitudes of all frequencies as a basis and an algorithm,

the digital logarithm and hence what is called a LOAD NUMBER is arrived at each CPI. The

load numbers in two adjacent CPIs are interpolated and a load pulse is generated every PRT

to load a 3-stage counter, the terminal count of the third stage after strobing is used as the

video pulses for jam strobe. This is sent to PPI for presentation. The interpolation gives the

presentation of a smooth strobe. A fixed IF attenuation of 30dB is introduced during the dead

range, in order to obtain distinct main lobe and side lobes for the jammer strobe indication.

JAMMER CLASSIFICATION

Jammer duty ratio count and jammer bandwidth count are generated using certain

algorithms comparing the magnitude (after MTI operation) over a 8 CPI bracket.

Depending on the values of these counts the jammer is classified as Low, Medium or High

duty as well as Narrow bandwidth, Medium bandwidth or Wide bandwidth. In each case 2

bits of data are generated and the classification is indicated on the frequency indication panel

(in system control unit), using LEDs.

RPM MONITORING CIRCUITS

This circuit can monitor in either test mode (local diagnostics) or in operate (i.e.

system) mode, the following parameters being indicated for two sets of numeric displays. Set

1 indicates while the values for a single scan while Set 2 dispays the values averaged over the

past 8 scans.

The parameters monitored are:

Probability of detection, percentage-indicated as a number in the form-(ZZZ)-with

BITE (targets) only.

Probability of false alarms, a No. (x 106)-indicated as a number-for all 16 filters in the

form-(XX.YY).

Probability of false alarms, a No. (x 106)-indicated as a number 4 single filter in the

form-(XXX.Y).


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With the help of DIP switches the above operation is selected.


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OUTPUT MONITORING FUNCTIONS

This card is mainly to see the D/A converted output of 3 types of the signal channels

of the signal processor on an oscilloscope. The card is designed to take 16 bits of data of any

3 channels, as the signal processor (MTD) hardware has got 3 main channels namely MTI,

FFT, ZVF.

CONTROL PANEL FUNCTIONS

Each of the cards has its card panel mounted on the front side. The control panel.


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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

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

receiver.


http://www.radartutorial.eu/08.transmitters/tx05.en.html#disadvantages




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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

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

in the Synchronizer.





http://www.radartutorial.eu/17.bauteile/bt21.en.html

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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.


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MAGNETRONMAGNETRON

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 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

GTBKIET.Six Months Training

filament leads

cathode pickup loop

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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

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


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

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.


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Figure 5: The high-frequency electrical field

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


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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

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%.


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Modes of Oscillation

The operation frequency depends on the sizes of the cavities and the interaction space

between anode and cathode. But the single cavities are coupled over the interaction space

with each other. Therefore several resonant frequencies exist for the complete system. Two of

the four possible waveforms of a magnetron with 8 cavities are in the figure 8 represented.

Several other modes of oscillation are possible (3/4π, 1/2π, 1/4π), but a magnetron operating

in the π mode has greater power and output and is the most commonly used.

Figure 8: Waveforms of the magnetron (Anode segments are represented „unwound”)

Strapping

Figure 9: cutaway view of a magnetron, showing the strapping rings and the slots.

So that a stable operational condition adapts in the optimal pi mode, two constructive

measures are possible:

Strapping rings:

The frequency of the π mode is separated from the frequency of the other modes by

strapping to ensure that the alternate segments have identical polarities. For the

pi mode, all parts of each strapping ring are at the same potential; but the two rings

have alternately opposing potentials. For other modes, however, a phase difference

exists between the successive segments connected to a given strapping ring which

causes current to flow in the straps.

Use of cavities of different resonance frequency

E.g. such a variant is the anode form „Rising Sun”.


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Magnetron coupling methods

Energy (rf) can be removed from a magnetron by means of a coupling loop. At

frequencies lower than 10,000 megahertz, the coupling loop is made by bending the inner

conductor of a coaxial line into a loop. The loop is then soldered to the end of the outer

conductor so that it projects into the cavity, as shown in figure 10, view (A). Locating the

loop at the end of the cavity, as shown in view (B), causes the magnetron to obtain sufficient

pickup at higher frequencies.

Figure 10: Magnetron coupling, view (A) and (B)

The segment-fed loop method is shown in view (C) of figure 11. The loop intercepts

the magnetic lines passing between cavities. The strap-fed loop method (view (D), intercepts

the energy between the strap and the segment. On the output side, the coaxial line feeds

another coaxial line directly or feeds a waveguide through a choke joint. The vacuum seal at

the inner conductor helps to support the line. Aperture, or slot, coupling is illustrated in view

(E). Energy is coupled directly to a waveguide through an iris.

Figure 11: Magnetron coupling, view (C), (D) and (E)


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Magnetron tuning

A tunable magnetron permits the system to be operated at a precise

frequency anywhere within a band of frequencies, as determined by magnetron

characteristics. The resonant frequency of a magnetron may be changed by

varying the inductance or capacitance of the resonant cavities.

Tuner frame

anode block

additionalinductivetuningelements

Figure 12: Inductive magnetron tuning

An example of a tunable magnetron is the M5114B used by the ATC- Radar ASR-

910. To reduce mutual interferences, the ASR-910 can work on different assigned

frequencies. The frequency of the transmitter must be tunable therefore. This magnetron is

provided with a mechanism to adjust the Tx- frequency of the ASR-910 exactly.

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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Pulse CompressionPulse Compression

This is a method which combines the high energy of a long pulse width

with the high resolution of a short pulse width. The pulse is frequency

modulated, which provides a method to further resolve targets which may have

overlapping returns. The pulse structure is shown in the figure 1.

Figure 1: separation of frequency modulated pulses

Since each part of the pulse has unique frequency, the returns can be completely separated.

This modulation or coding can be either

FM (frequency modulation)

o linear (chirp radar) or

o non-linear or

PM (phase modulation).

Now the receiver is able to separate targets with overlapping of noise. The received

echo is processed in the receiver by the compression filter. The compression filter readjusts the

relative phases of the frequency components so that a narrow or compressed pulse is again

produced. The radar therefore obtains a better maximum range than it is expected because of the

conventional radar equation.



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Figure 2: short pulse (blue) and a long pulse with intrapulsemodulation (green)

The ability of the receiver to improve the range resolution over that of the

conventional system is called.0

the pulse compression ratio (PCR). For example a pulse compression ratio of 50:1

means that the system range resolution is reduced by 1/50 of the conventional system.

Alternatively, the factor of improvement is given the symbol PCR, which can be used

as a number in the range resolution formula, which now becomes:

Rres = c0 · Pw · ( 2 · PCR)

The compression ratio is equal to the number of sub pulses in the waveform, i.e., the

number of elements in the code. The range resolution is therefore proportional to the time

duration of one element of the code. The maximum range is increased by the PCR.

The minimum range is not improved by the process. The full pulse width still applies

to the transmission, which requires the duplexer to remained aligned to the transmitter

throughout the pulse. Therefore Rmin is unaffected.


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Table 1: Advantages and disadvantages of the pulse compression

AdvantagesDisadvantages

lower pulse-powertherefore suitable for Solid-State-amplifier

high wiring effort

higher maximum range bad minimum range

good range resolution time-sidelobes

better jamming immunity

difficulter reconnaissance

Pulse compression with linear FM waveform

At this pulse compression method the transmitting pulse has a linear FM waveform.

This has the advantage that the wiring still can relatively be kept simple. However, the linear

frequency modulation has the disadvantage that jamming signals can be produced relatively

easily by so-called „Sweeper”.

The block diagram on the picture illustrates, in more detail, the principles of a pulse

compression filter.





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Figure 3: Block diagram (an animation as explanation of the mode of operation

The compression filter are simply dispersive delay lines with a delay, which is a linear

function of the frequency. The compression filter allows the end of the pulse to „catch up” to

the beginning, and produces a narrower output pulse with a higher amplitude.

As an example of an application of the pulse compression with linear FM waveform

the RRP-117 can be mentioned.

Filters for linear FM pulse compression radars are now based on two main types.



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Digital processing (following of the A/D- conversion).

Surface acoustic wave devices .

Figure 4: View of the Time-Side-Lobes

Time-Side-Lobes

The output of the compression filter consists of the compressed pulse accompanied by

responses at other times (i.e., at other ranges), called time or range sidelobes. The figure

shows a view of the compressed pulse of a chirp radar at an oscilloscope and at a ppi-scope

sector.

Amplitude weighting of the output signals may be used to reduce the time sidelobes to

an acceptable level. Weighting on reception only results a filter „mismatch” and some loss of

signal to noise ratio.

The sidelobe levels are an important parameter when specifying a pulse compression

radar. The application of weighting functions can reduce time sidelobes to the order of

30 db's.


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Pulse compression with non-linear FM waveform

The non-linear FM waveform has several distinct advantages. The non-linear FM

waveform requires no amplitude weighting for time-sidelobe suppression since the FM

modulation of the waveform is designed to provide the desired amplitude spectrum, i.e., low

sidelobe levels of the compressed pulse can be achieved without using amplitude weighting.

Phase-Coded Pulse Compression

Figure 8: diagram of a phase-coded pulse compression

Phase-coded waveforms differ from FM waveforms in that the long pulse is sub-

divided into a number of shorter sub pulses. Generally, each sub pulse corresponds with a

range bin. The sub pulses are of equal time duration; each is transmitted with a particular

phase. The phase of each sub-pulse is selected in accordance with a phase code. The most

widely used type of phase coding is binary coding.

The binary code consists of a sequence of either +1 and -1. The phase of the

transmitted signal alternates between 0 and 180° in accordance with the sequence of

elements, in the phase code, as shown on the figure. Since the transmitted frequency is

usually not a multiple of the reciprocal of the sub pulse width, the coded signal is generally

discontinuous at the phase-reversal points.

The selection of the so called random 0, π phases is in fact critical. A special class of

binary codes is the optimum, or Barker, codes. They are optimum in the sense that they

provide low sidelobes, which are all of equal magnitude. Only a small number of these

optimum codes exist. They are shown on the beside table. A computer based study searched

for Barker codes up to 6000, and obtained only 13 as the maximum value.

It will be noted that there are none greater than 13 which implies a maximum

compression ratio of 13, which is rather low. The sidelobe level is -22.3 db.


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Radar complexity

Radar — an old acronym for radio detection and ranging — has always been a

demanding technology, but at no time more so than today. Essentially, it works by emitting

radio frequency (RF) signals at particular frequencies, and then listening for the signal's

return — or "bounce" — off of targets of interest. At it simplest theoretical level, this does

not sound like a big deal, but putting the theory into useful practice is where advanced

technology — and designers headaches — come in.

Several different kinds of radar systems are in use today, including

continuous wave (CW), pulsed, pulsed-Doppler, phased array, and synthetic

aperture.

The Mercury RACE++ Series PowerStream 510 system is used in applications such as advanced radar, sonar, imaging, and inspection.

CW radar continually transmits energy toward the desired target and receives a

reflection of this "continuous wave." These kinds of radar are useful for determining a target's

velocity by using the Doppler effect to compare differences in the transmitted and received

signals. These radar systems, however, have difficulty determining the target's range, or how

far way it is.


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Pulsed radar, on the other hand, sends out a series of short RF pulses. By measuring

how long it takes to receive the returns from these pulses, system operators can estimate the

range to the target. Pulse Doppler radar, in addition, uses Doppler shifts with radar pulses to

determine the velocities of moving targets. These systems can determine the velocities,

angles, and ranges of targets. These added capabilities, however, make pulse Doppler radar

much more compute-intensive than simple pulsed radar.

Phased array radar systems, meanwhile, arrange large numbers of transceiver modules

arranged on flat or curved surface. The system controls the phase — or a slight variation in

the transmit and receive time of groups of transceiver modules — with computer commands,

and in essence "steers" the radar beams quickly, enabling the phased array radar to scan

specific areas quickly, "stare" at targets of interest, or do a variety of other tasks, all without

the need to move the transceiver array mechanically.

The ability of phased array radar systems to manipulate their groups of transceivers

also gives this system an "adaptive array" capability, which not only can steer beams quickly,

but also enables the system to shift the focus of radar beams to "null out" electronic

interference or jamming.

Precise radar images most often come from synthetic aperture radar systems. These

so-called "side-looking" aircraft-mounted systems — such as the U.S. Joint Surveillance and

Target Attack Radar System known as Joint STARS — produce two-dimensional images,

where one dimension is the range, or distance from the radar to the target using Doppler

processing, and the other dimension is the azimuth, which requires a physically large antenna

to focus the transmitted and received RF signal into a sharp beam. Synthetic aperture radar,

better known as SAR — collects data over a long distance, and processes the data as if it

came from a physically long antenna. SAR requires extremely fast processing and very fast

signal sampling rates.

After all this, the way in which a radar system processes information also can change

the nature of the radar system itself. Take radar pulse compression, for example. This is a

technique that makes the most of the radar's sensitivity and resolution by balancing the

effects of radar pulse duration, radar pulse power, and radar pulse bandwidth.


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Pulse compression uses Fast Fourier Transform (FFT) processing to massage the

signal as it comes in from the A-D converters. "With pulse compression, you need to take an

FFT of the radar signal to remove as much stuff that doesn't belong to the return signals as

possible," explains Rodger Hosking, vice president of Pentek Inc. of Upper Saddle River,

N.J., which supplies single-board processors to radar designers.

"So they send out a 'chirp', or a unique signal that doesn't exist in nature," Hosking

continues. "You convert what comes back into frequency domain, and take the frequency

domain of your outgoing pulse and correlate the two. You extract only the part of the signal

coming back that has to do with the outgoing pulse. Then you do an inverse FFT, and you get

a very nice 'blip'." Until recently, Hosking explains, that kind of processing has been done in

analog, and in DSPs. "It's a very demanding problem to do in real time."

Processing challenges

One of the first and most serious problems confronting radar systems involves noise

and clutter in the return signal. After all, RF energy bounces off a lot more than simply the

target of interest; it bounces off trees, buildings, mountains, vehicles, and about anything else

in its path, and in various degrees of intensity depending on the reflecting materials.

One of the most important tasks of modern radar systems is to reject, or "filter-out,"

return signals that are not of interest. Next, radar users today want far more from their

systems than simply the proverbial "blip on the screen." Many modern radar systems are able

to filter their return signals so finely that these signals produce an actual image of the target.

Finally, most radar systems — particularly those for military and aerospace applications —

must operate in real time. All these factors combine to produce a challenge of staggering

computational intensity for all but the simplest radar systems.

Today's radar systems digitize their signals very quickly after receiving them. After

analog-to-digital conversion, advanced algorithms process the signals to eliminate noise by

filtering out unwanted portions of the signal, perform Doppler calculations to help determine

range, and do many other operations to prepare the data for further processing later that will

do tasks like enter radar signatures into databases and display the information on graphical

screens.


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In the front-end "pre-processing" stage, the processor of choice increasingly is the

field programmable gate array (FPGA) from companies such as Xilinx Inc. in San Jose,

Calif., and Actel Corp. in Sunnyvale, Calif. This is primarily a move away from DSPs on the

front end, experts say. At the same time, systems designers rely more heavily than ever

before on high-end general-purpose processors such as the Altivec on the back end.

The rise of FPGAs

FPGAs only recently have achieved the kinds of densities necessary for fast and

demanding radar front-end processing, experts say. "FPGAs are now so much bigger and so

much faster than they were years ago," says Jane Donaldson, president and chief executive

officer of Annapolis Micro Systems Inc. a radar processing firm in Annapolis, Md.

"Normally you can have 30 million gates in a single VME slot, while five years ago you

would struggle to get a million gates. You have enough processing power now to solve the

problem."

This fast expansion in number of gates per device has made all the difference for

radar systems integrators and their signal processing systems providers. "Over the past year

we have been seeing a swing to more FPGA processing, particularly at the front end of radar

and sonar processing, for repetitive math functions, filtering, and things that go on at the front

end of the processor," says Stuart Heptonstall, product marketing manager for DSP products

at Radstone Technology, a single-board radar processor supplier in Towcester, England.

"FPGAs you can code exactly how you want, to keep them chunking away at that front-end

data," he says, and enable designers to change the front-end processor for different platforms.

"Our customers, the prime contractors, all are looking to put FPGAs as close to the

radar sensing elements as possible — the antennas, transmitters, and receivers — to do pre-

processing," says Philip Lindsay, northeast regional sales manager at Thales Computers Inc.

in Raleigh, N.C. FPGAs, he says, are valuable for "massaging the data and lining it up so it is

amenable to quick-corner turns, or quick FFTs, or quick FIRs [finite responses] so it can be

processed almost immediately by the CPUs. They get the data as they need it, and you reduce

latency."

The radar signal-processing challenge is not fundamentally different today

from how it was decades ago; what is changed is the processing approaches,


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which is where FPGAs come in today, says Larry Nork, director of radar business

development at Mercury Computer Systems in Chelmsford, Mass.

The Lockheed Martin Medium Extended Air Defence System (MEADS) uses a UHF

surveillance radar and X-band Multifunction Fire Control Radar.

"In radar signal processing. What you needed in the past you need today, but you

might do it more efficiently today," Nork explains. "You take channel equalization, phase

compensation, and follow that up with pulse compression done with convolution processing

where you have an FFT and a complex multiply, then do a inverse FFT, and that allows you

to match filter processing on the radar return. Those are data-independent functions that are

performed in a streaming fashion no mater what is coming into the input of the radar receiver,

where the same function is repeated time after time, with no need for programmability. So

you can add efficiency to the processing by using FPGAs, as opposed to using a

programmable RISC processor."

Still, Radstone's Heptonstall cautions that the necessary investment in FPGAs is

relatively high, and implementers also must invest a lot of time providing the FPGA function.

The FPGA programmer must write his own VHDL FFT code to engineer that solution, while

today's DSPs often are easier to program than are FPGAs.

Many systems designers insist that DSPs still have a role in radar processing; the trick

is to determine the niche that FPGAs and DSP processors serve, says Bernard Pelon, director


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of product research at CSPI Inc., a radar processing supplier in Billerica, Mass. Either the

FPGA or DSP might do better on some classes of problems, but might be more difficult to

use, he says. "That may be why we begin to look at FPGAs and specialized processors. We

need to understand where each applies and balance them out."

No matter the choice of the FPGA or DSP, Pelon points out that both represent a step

away from trends toward general-purpose processors that are not application specific,

although he says FPGAs are farther away from the general-purpose ideal than are today's

DSPs. "In both cases you lose generality; there is no question that they are not general-

purpose hardware," he says. "What we are facing is a non-standard world. The FPGA inside

is a profusion of non-standard things, such as how you connect your gates, so with the

specialized DSP there is an advantage. Now we need to define a standard internal FPGA bus,

and we are nowhere close to that."

As far as CSPI is concerned, "we lean to FPGA and specialized DSP; there is space

for both, Pelon says. They are both in the spatial function side." He points to new generations

of DSPs, such as the Analog Devices TigerSHARC, and the FastMATH and FastMIPS

architectures from Intrinsity Inc. in Austin, Texas, that might cause radar designers to take

another look at DSPs — either for front- or back-end processing.

The PowerPC Altivec

On back-end radar processing, meanwhile, "two to three years ago we started seeing a

shift away from dedicated DSP chips over to the PowerPC processors," Heptonstall says. The

DSP chips required coding in low-level languages, such as assembler, "which is great if you

know how to do it, and have the time, but we need to get to market quicker today," he says.

"It's too much of a pain and an investment to program in assembler all the time."

Rapid increases in the PowerPC Altivec's clock speed and other performance

parameters started gaining the attention of radar systems integrators about three years ago

when Motorola first introduced the Altivec version of the venerable PowerPC

microprocessor, CSPI's Pelon says.

"Before Altivec, PowerPC was not judged to be very attractive, but after Altivec it

was judged to be a very good solution," Pelon says. It was significant because you were


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bringing DSP into a scalar architecture. You increased by a factor of four the operations you

could run. It was fantastic news for anyone who had chosen the PowerPC architecture."

Six years ago, for example, the most advanced PowerPC processors ran at clock

speeds of 200 MHz, "but then, with the Altivec, you had 400 MHz — four times the

operations, plus the processor's L2 cache was improved. So overall you had a factor of 20

improvement for FFT processing" Pelon says. PowerPC Altivec processors soon will be

available that run at clock speeds as fast as 1 GHz.

Software issues also make up an attractive aspect of general-purpose processors such

as the Altivec, experts say. Radstone's Heptonstall says he believes the Motorola suite of

advanced PowerPC Altivec processors "have much more easy user interfaces and support for

off-the-shelf real-time operating systems such as Wind River VX Works, Linux,

LynuxWorks LynxOS, and the OSE real-time operating system," than do the industry's DSP

offerings. "The processors have a lot of momentum for these operating systems and have

commonality with slot-1 single-board computers, which are predominantly the PowerPC

processor. It makes the whole thing easier and more user friendly," he says.

Aside from its advantages in speed, the PowerPC Altivec also offers designers the

benefits of a standard off-the-shelf architecture that is well understood throughout the

industry. "The benefit of standard hardware and software is concurrent engineering," says

CSPI's Pelon. "If I have a piece of software that you can run on any workstation, then you can

have several players doing concurrent engineering, and that couldn't be done in the past. That

translates into minimizing development time, which is very important in terms of effective

results and solutions and quality."

Another factor running in the Altivec's favor is the new crop of fast switched-network

architectures, such as RapidIO, Infiniband, and StarFabric, which promise to boost the

Altivec's power when many processors combine on a network. In terms of fabric, none of this

can work without a very fast fabric to connect general-purpose processor nodes with some of

the more specialized nodes," Pelon says. "We need more than ever a high-speed

interconnect."


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Architectural considerations

Often the type of radar system under development will help determine the signal-

processing architecture. Large fixed-site radar systems with virtually unlimited capacity for

space, weight, and power, for example, might accommodate a processing architecture heavy

on general-purpose processors. Yet fighter aircraft radar, which places a premium on small

size, lightweight, and low power consumption, might require a processor architecture heavy

on FPGA and DSPs, and might not accommodate general-purpose processors at all.

"The requirements for small-volume and low weight in advanced

applications rely heavily on FPGAs. Other areas where we are not as restricted is

where we can use the off-the-shelf processors," explains Kam Insky, manager of

radar engineering project management at Lockheed Martin Naval Electronics &

Surveillance Systems in Syracuse, N.Y. Lockheed Martin Syracuse provides a

wide variety of radar systems, from large ground-based air traffic control

systems, to space-constrained airborne systems.

The AN/TPS-77 Tactical Transportable Radar can be operational in less than one hour.

"In our advanced ground and airborne systems, where we not only deal with volume

and weight, but also in advanced technologies such as digital advanced beamforming, we use


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a hybrid — or FPGA — approach, primarily on the front end," Insky explains. "For backend

data processing, we use general-purpose processors" such as the PowerPC.

"There are niches," Insky points out. "I see an evolution to more use of FPGAs than

the dedicated DSPs, but we still have a product that relies heavily on DSPs" — an airborne

system that uses the Analog Devices SHARC, he says. It is primarily driven by application

— and in our applications now, we see continued use of FPGAs."

Popularity of the Altivec helps designers re-invent the DSP

Although some radar systems designers may be writing off the digital signal processor

(DSP) as a thing of the past in radar processing systems, proponents of the DSP say word of

their passing is premature.

The recently released TigerSHARC DSP from Analog Devices in Norwood, Mass., is

perhaps the strongest argument against the demise of the DSP in radar applications. Yet the

TigerSHARC and other new DSPs are competing head-to-head with the PowerPC Altivec

microprocessor, not field programmable gate arrays (FPGAs), in radar applications, experts

say.

The TigerSHARC is an ultra high-performance static superscalar architecture for

computationally demanding applications, and combines elements of RISC, VLIW, and

standard DSP processors for 1-, 8-, 16-, and 32-bit fixed and floating-point processing.

The original Analog Devices SHARC 21060 DSP — short for Super Harvard

Architecture — dominated radar and sonar signal processing applications throughout the

1990s, yet gradually gave way to fast Altivec processors as the new century dawned.

DSP proponents say the new TigerSHARC will give a big boost not only to the

Analog Devices DSP product line, but also to DSP architectures across the board.

"We've seen with the introduction of the TigerSHARC, our competitive environment

changed 180 degrees; historically when we introduced the SHARC, we competed with Texas

Instruments [DSPs}. Now with the introduction of the TigerSHARC, we are competing with

the Altivec," says Darren Taylor, vice president of sales and marketing at BittWare Inc., a

single-board DSP designer in Concord, N.H.


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"The TigerSHARC serves very well in some of these radar applications; we are seeing

it across the board for radar systems," particularly for air traffic control, over-the-horizon,

and 3D-based radar applications, Taylor says.

The European radar manufacturer Alenia Marconi, for example, is using the

TigerSHARC as their processor of choice for next-generation 3D air traffic control radar

systems, Taylor says. "They did this because of the ability to do the continuous data

movement and processing."

Taylor admits that the Altivec G4 general-purpose processor can crunch data faster

than the TigerSHARC can, "but you need to get the data in and the data out," he says. "That

is where the TigerSHARC does much better in the real world."

In addition, Taylor says, the TigerSHARC is more attractive in terms of power

consumption. "The G4s are huge consumers of power" from five to 20 watts per chip, he

says. "You are limited to the number of processors you can get on a board."


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