INDUSTRIAL TRAINING REPORT (31st MAY – 09th JULY 2011)
ON REPORTER RADAR TRANSMITTER AND VARIOUS ROTATIONAL PROGRAMS
Submitted By:PRATEEK AGGARWAL Branch- ECE UPT No.- 125/B.TECH/2011 Roll No.- 09102297
1
ACKNOWLEDGEMENT
I wish to express my sincere thanks to the Management of Bharat Electronics Limited (BEL), Bharat Nagar, Ghaziabad including the Head of the Human Resou esourc rcee
Devel evelop opme ment nt
Depa Depart rtme ment nt
Mrs.
VANITA
BHANDARI
(MANAGER, HRD) for providing me an opportunity to receive training in this important Industrial Unit manufacturing electronics equipment in our country.
I am deeply indebted to Mr. DHYAN SINGH , (Deputy General Manager, Mr. A.K A.K.. SAK SAKSEN SENA A (Manager,PA-R Radar Radar Divisi Division on PA-R2) PA-R2) AND Mr. (Manager,PA-R2) 2) for
sparing sparing his most special special time in providing guidance to me in training. Without Without his wise counsel, inestimable encouragement, it would have been difficult for me to have have know knowle ledg dgee of the the func functi tion onin ing g of vari variou ouss types types of elec electr tron onic icss equipment particularly radars. Gratitude is also due to him for his constant guidance and direction in writing this piece of work.
Special thanks to Mr. DINESH KUMAR (Department (Department of Radar Transmitter) Transmitter) for their valuable guidance, help and cooperation.
It is a great pleasure to express my heart full thanks to staff of BEL who helped me directly or indirectly throughout the successful completion of my training. There is no substitution to ‘Team Work’; this is one of the lessons I learnt during my training in BHARAT ELECTRONICS LIMITED.
2
ACKNOWLEDGEMENT
I wish to express my sincere thanks to the Management of Bharat Electronics Limited (BEL), Bharat Nagar, Ghaziabad including the Head of the Human Resou esourc rcee
Devel evelop opme ment nt
Depa Depart rtme ment nt
Mrs.
VANITA
BHANDARI
(MANAGER, HRD) for providing me an opportunity to receive training in this important Industrial Unit manufacturing electronics equipment in our country.
I am deeply indebted to Mr. DHYAN SINGH , (Deputy General Manager, Mr. A.K A.K.. SAK SAKSEN SENA A (Manager,PA-R Radar Radar Divisi Division on PA-R2) PA-R2) AND Mr. (Manager,PA-R2) 2) for
sparing sparing his most special special time in providing guidance to me in training. Without Without his wise counsel, inestimable encouragement, it would have been difficult for me to have have know knowle ledg dgee of the the func functi tion onin ing g of vari variou ouss types types of elec electr tron onic icss equipment particularly radars. Gratitude is also due to him for his constant guidance and direction in writing this piece of work.
Special thanks to Mr. DINESH KUMAR (Department (Department of Radar Transmitter) Transmitter) for their valuable guidance, help and cooperation.
It is a great pleasure to express my heart full thanks to staff of BEL who helped me directly or indirectly throughout the successful completion of my training. There is no substitution to ‘Team Work’; this is one of the lessons I learnt during my training in BHARAT ELECTRONICS LIMITED.
2
C ERTIFICATE
This is to certify that PRATEEK AGGARWAL of B.TECH 2ND YEAR(ECE) of JIIT , NOIDA has successfully completed his industrial
training under guidance of Mr. A.K.Saxena, Manager(PA-RADAR) and Mr. Dinesh Kumar in BHARAT ELECTRONICS LIMITED, GHAZIABAD
from 31th may to 9th july 2011.
A project titled STUDY OF TRANSMITTER OF RADAR was assigned to him in this period. He worked hard and diligently and completed his project in time. He took lot of initiative in learning about RADAR SYSTEM AND AND
VARI VARIOU OUS S
TEST TE ST
INST INSTRU RUME MENT NTS/ S/ME METH THOD ODS. S.
His His
over overal alll
performance during the project was excellent. We wish him all success in his career.
Mr.Dinesh kumar
Mr. A.K.Saxena ___________
(PA-RADAR2)
(PA-RADAR2)
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PREFACE
With With the the ongo ongoin ing g revo revolu luti tion on in elec electr tron onic icss and and comm commun unic icat atio ion n wher wheree innovations are taking place at the blink of eye, it is impossible to keep pace with the emerging trends.
Excellence is an attitude that the whole of the human race is born with. It is the environment that makes sure that whether the result of this attitude is visible or otherwise. otherwise. A well planned, properly executed and evaluated evaluated industrial industrial training helps a lot in collating a professional attitude. It provides a linkage between a student and industry to develop an awareness of industrial approach to problem solving, based on a broad understanding of process and mode of operation of organization.
During this period, the student gets the real experience for working in the industry environment. Most of the theoretical knowledge that has been gained during the course of their studies is put to test here. Apart from this the student gets an opportunity to learn the latest technology, which immensely helps in them in building their career.
I had had the the oppo opport rtun unit ity y to have have a real real expe experie rienc ncee on many many vent ventur ures es,, whic which h increased my sphere of knowledge to great extent. I got a chance to learn many new technologies technologies and also interfaced interfaced too many instruments. instruments. And all this credit goes to organization BHARAT ELECTRONICS LIMITED.
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CONTENTS
S.No.
Topics
1
BEL
Page Nos.
Introduction
5-8
2
Manufacturing Units
3
BEL (Ghaziabad Unit)
11
4
Product Ranges
12
5
Services of BEL
13
6
Rotation Program
14
Test Equipment and Automations
PCB Fabrication
Quality Control Works-Radar
Work Assembly-Communication
Magnetics
Microwave Lab
9-10
7
Radar
22
11
Signal Processing Unit
41
12
Fully Coherent Radar
45
13
Magnetron
48
14
Conclusion
55
BHARAT ELECTRONICS LIMITED
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INTRODUCTION India, as a country, has been very lucky with regard to the introduction of telecom products. The first telegraph link was commissioned between Calcutta and Diamond Harbor in the year 1852, which was invented in 1876. First wireless communication equipment were introduced in Indian Army in the year 1909 with the discovery of Radio waves in 1887 by Hertz and demonstration of first wireless link in the year 1905 by Marconi and Vacuum Tube in 1906. Setting up of radio station for broadcast and other telecom facilities almost immediately after their commercial introduction abroad followed this. After independence of India in 1947 and adoption of its constitution in 1950, the government was seized with the plans to lay the foundations of a strong, self-sufficient modern India. On the industrial front, Industrial Policy Resolution (IPR) was announced in the year 1952. It was recognized that in certain core sectors infrastructure facilities require huge investments, which cannot be met by private sector and as such the idea of Public Sector Enterprises (PSE) was mooted. With telecom and electronics recognized among the core sectors, Indian Telephone Industry, now renamed as ITI Limited, was formed in 1953 to undertake local manufacture of telephone equipment, which were of electro-mechanical nature at that stage. Hindustan Cable Limited was also started to take care of telecom cables.
Bharat Electronics Limited (BEL) was established in 1954 as a public Sector Enterprise under the administrative control of Ministry of Defence as the fountainhead to manufacture and supply electronics components and equipment. BEL, with a noteworthy history of pioneering achievements, has met the requirement of state-of-art professional electronic equipment for Defence, broadcasting, civil Defence and telecommunications as well as the component requirement of entertainment and medical X-ray industry. Over the years, BEL has grown to a multi-product, multi-unit, and technology driven company with track record of a profit earning PSU.
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The company has a unique position in India of having dealt with all the generations of electronic component and equipment. Having started with a HF receiver in collaboration with T-CSF of France, the company’s equipment designs have had a long voyage through the hybrid, solid-state discrete component to the state of art integrated circuit technology. In the component arena also, the company established its own electron value manufacturing facility. It moved on to semiconductors with the manufacture of germanium and silicon devices and then to the manufacture of Integrated circuits. To keep in pace with the component and technology, its manufacturing and products assurance facilities have also undergone sea change. The design groups have CADD facility; the manufacturing has CNC machines and a Mass Manufacture Facility. QC checks are preformed with multi-dimensional profile measurement machines, Automatic testing machines, environmental labs to check extreme weather and other operational conditions. All these facilities have been established to meet the stringent requirements of MIL grade systems.
Today BEL’s infrastructure is spread over nine locations with 29 production divisions having ISO-9001/9002 accreditation. Product mix of the company are spread over the entire Electro-magnetic (EM) sp 3ectrum ranging from tiny audio frequency semiconductor to huge radar systems and X-ray tubes on the upper edge of the spectrum. Its manufacturing units have special focus towards the products ranges like Defence Communication, Rader’s, Optical & Opto-electronics, Telecommunication, sound and Vision Broadcasting, Electronic Components, etc.
Besides manufacturing and supply of a wide variety of products, BEL offers a variety of services like Telecom and Rader Systems Consultancy, Contract Manufacturing, Calibration of Test & Measuring Instruments, etc. At the moment, the company is installing MSSR radar at important airports under the modernization of airports plan of National Airport Authority (NAA).
BEL has nurtured and built a strong in-house R&D base by absorbing technologies from more than 50 leading companies worldwide and DRDO Labs for a wide range of products. A team of more than 800 engineers is working in R&D. Each unit has its own R&D Division to bring out new products to the production lines. Central Research Laboratory (CRL) at Bangalore and Ghaziabad works as independent agency to undertake contemporary design work on state-of-art and futuristic technologies. About 70% of BEL’s products are of 7
in-house design.
BEL was among the first Indian companies to manufacture computer parts and peripherals under arrangement with International Computers India Limited (ICIL) in 1970s. BEL assembled a limited number of 1901 systems under the arrangement with ICIL. However, following Government’s decision to restrict the computer manufacture to ECIL, BEL could not progress in its computer manufacturing plans. As many of its equipment were microprocessor based, the company, Continued to develop computers based application, both hardware and software. Most of its software requirements are in real time. EMCCA, software intensive navel ships control and command system is probably one of the first projects of its nature in India and Asia.
BEL has won a number of national and international awards for Import Substitution, Productivity, Quality, Safety, Standardization etc. BEL was ranked No. 1 in the field of Electronics and 46th overall among the top 1000 private and public sector undertakings in India by the Business Standard in its special supplement “The BS 1000 (1997-98)”. BEL was listed 3rd among the Mini Rattan’s (Category II) by the Government of India, 49th among Asia’s top 100 worldwide Defence Companies by the Defence News, USA.
CORPORATE MOTTO , MISSION AND OBJECTIVES: 8
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 UNITS
BANGALORE (KANARATAKA) BEL started its production activities in Bangalore on 1954 with 400W high frequency (HF) transmitter and communication receiver for the Army. Since then, the Bangalore Complex has grown to specialize in communication and Radar/Sonar Systems for the Army, Navy and Air-force.
BEL’s in-house R&D and successful tie-ups with foreign Defence companies and Indian Defence Laboratories has seen the development and production of over 300 products in Bangalore alone. The Unit has now diversified into manufacturing of electronic products for the civilian customers such as DoT, VSNL, AIR and Doordarshan, Meteorological Dept., ISRO, Police, Civil Aviation and Railways. As an aid to Electorate, the unit has developed Electronic Voting Machines that are produced at its Mass Manufacturing Facility (MMF).
GHAZIABAD (UTTER PRADESH) The second largest Unit at Ghaziabad was set up in 1974 to manufacture special types of radar for the Air Defence Ground Environment Systems (Plan ADGES). The Unit provides Communication Systems to the Defence Forces and Microwave Communication Links to the various departments of the State and Central Govt. and other users. The Unit’s product range included Static and Mobile Radar, Tropo scatter equipment, professional grade Antennae and Microwave components.
PUNE (MAHARASHTRA) This Unit was started in 1979 to manufacture Image Converter Tubes. Subsequently, Magnesium Manganese-dioxide Batteries, Lithium Sulphur Batteries and X-ray Tubes/Cables were added to the product range. At the present the Laser Range Finders for the Defence services.
MACHILIPATNAM (ANDHRA PRADESH) The Andhra Scientific Co. at Machilipatnam, manufacturing Optics/Opto-electronic
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equipment was integrated with BEL in 1983. the product line includes passive Night Vision Equipment, Binoculars and Goggles, Periscopes, Gun Sights, Surgical Microscope and Optical Sights and Mussel Reference Systems for tank fire control systems. The Unit has successfully diversified to making the Surgical Microscope with zoom facilities.
PANCHKULA (HARYANA) To cater the growing needs of Defence Communications, this Unit was established in 1985. Professional grade Radio-communication Equipment in VHF and UHF ranges entirely developed by BEL and required by the Defence services are being met from this Unit.
CHENNAI (TAMIL NADU) In 1985, BEL established another Unit at Chennai to facilitate manufacture of Gun Control Equipment required for the integration and installation and the Vijay anta tanks. The Unit is now manufacturing Stabilizer Systems for T-72 tanks, Infantry Combat Vehicles BMP-II; Commander’s Panoramic Sights & Tank Laser Sights are among others.
KOTDWARA (UTTER PRADESH) In 1986, BEL STARTED A unit at Kotdwara to manufacture Telecommunication Equipment for both Defence and civilian customers. Focus is being given on the requirement of the Switching Equipment.
TALOJA (MAHARASHTRA) For the manufacture of B/W TV Glass bulbs, this plant was established in collaboration with coming, France in 1986. The Unit is now fully mobilized to manufacture
HYDERABAD (ANDHRA PRADESH) To coordinate with the major Defence R&D Laboratories located in Hyderabad, DLRL, DRDL and DMRL, BEL established a Unit at Hyderabad in 1986. Force Multiplier Systems are manufactured here for the Defence services 20’’ glass bulbs indigenously.
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BEL GHAZIABAD UNIT Formation In the mid 60’s, while reviewing the Defence requirement of the country, the government focused its attention to strengthen the Air Defence system, in particular the ground electronics system support, for the air Defence network. This led to the formulation of a very major plan for an integrated Air Defence Ground Environment System known as the plan ADGES with Prime Minister as the presiding officer of the apex review committee .At about the same time, Public attention was focused on the report of the Bhabha committee on the development and production of electronic equipment. The ministry of Defence immediately realized the need to establish production capacity for meeting the electronic equipment requirements for its plan ADGES. BEL was then inserted with the task of meeting the development and production requirement for the plan ADGES and in view of the importance of the project it was decided to create additional capacity at a second unit of the company. In December 1970 the Govt. sanctioned an additional unit for BEL. In 1971, the industrial license for manufacture of radar and microwave equipment was obtained, 1972 saw the commencement of construction activities and production was launched in 1974. Over the years, the unit has successfully manufactured a wide variety of equipment needed for Defence and civil use. It has also installed and commissioned a large number of systems on turnkey basis. The unit enjoys a unique status as manufacture of IFF systems needed to match a variety of primary raiders. More than 30 versions of IFF’s have already been supplied traveling the path from vacuum technology to solid-state to latest Microwave Component based system.
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PRODUCT RANGES The product ranges today of the company are:
RADAR SYSTEMS 3-Dimensional High Power Static and Mobile Radar for the Air Force. Low Flying Detection Radar for both the Army and the Air force. Tactical Control Radar System for the Army. Battlefield Surveillance Rader for the Army. IFF Mk-X Radar systems for the Defence and export. ASR/MSSR systems for Civil Aviation. Radar & allied systems Data Processing Systems.
COMMUNICATIONS Digital Static Tropo scatters Communication Systems for the Air Force. Digital Mobile Tropo scatters communication System for the Air Force and Army. VHF, UHF & Microwave Communication Equipment. Bulk Encryption Equipment. Turnkey communication Systems Projects for Defence & civil users. Static and Mobile Satellite Communication Systems for Defence. Telemetry /Tele-control Systems.
ANTENNA Antennae for Radar, Terrestrial & Satellite Communication Systems. Antennae for TV Satellite Receive and Broadcast applications. Antennae for Line-of-sight Microwave Communication Systems.
MICROWAVE COMPONENT Active Microwave components like LNAs, Synthesizer, and Receivers etc. Passive Microwave components like Double Balanced Mixers, etc.
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SERVICES OF BHARAT ELECTRONICS LIMITED (BEL):-
DEFENCE PRODUCTS: Naval System Military Communication Equipment Radars Tele Communication & Broadcasting Services Opto Electronics Electronic Warfare Tank Electronics
NON-DEFENCE PRODUCTS: Electronic Voting Machine Solar Products Simputer DTH
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ROTATION PROGRAM Under this students are introduced to the company by putting them under a rotation program to various departments. The several departments where I had gone under my rotational program are: 1.
Test Equipment and Automation
2.
Quality Control Works-Radar
3.
Work Assembly- Communication
4.
Microwave lab
Rotation period was to give us a brief insight of the company’s functioning and knowledge of the various departments. A brief idea of the jobs done at the particular departments was given. The cooperative staff at the various departments made the learning process very interesting , which allowed me to know about the company in a very short time.
TEST EQUIPMENT AND AUTOMATION This department deals with the various instruments used in BEL. There are 300 equipments and they are of 16 types. Examples of some test equipments are: Oscilloscope(CRO) Multimeter Signal Analyzer Logical Pulsar Counter Function Generator etc.
Mainly the calibration of instruments is carried out here. They are compared with the standard of National Physical Laboratory (NPL). So, it is said to be one set down to NPL. As every instrument has a calibration period after which the accuracy of the instrument falls from the required standards. So if any of the instruments is not working properly, it is being sent here for its correct calibration. To calibrate instruments software techniques are used
15
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. A
--- Physical and Mechanical defects.
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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.
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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 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 :
Material 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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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
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vi)
Amplifiers and Accessories
22
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
23
meteorological detection of precipitation, air traffic control, police detection of speeding traffic, and by the military.
Several inventors, scientists, and engineers contributed to the development of radar. The use of radio waves to detect "the presence of distant metallic objects via radio waves" was first implemented in 1904 by Christian Hülsmeyer , who demonstrated the feasibility of detecting the presence of ships in dense fog and received a patent for radar as Reichspatent Nr. 165546. Another of the first working models was produced by Hungarian Zoltán Bay in 1936 at the Tungsram laboratory
BASIC PRINCIPLE Echo and Doppler Shift Echo is something you experience all the time. If you shout into a well or a canyon, the echo comes back a moment later. The echo occurs because some of the sound waves in your shout reflect off of a surface (either the water at the bottom of the well or the canyon wall on the far side) and travel back to your ears. The length of time between the moments you shout and the distance between you and the surface that creates the echo determines the moment that you hear the echo. Doppler shift is also common. You probably experience it daily (often without realizing it). Doppler shift occurs when sound is generated by, or reflected off of, a moving object. Doppler shift in the extreme creates sonic booms (see below). Here's how to understand Doppler shift (you may also want to try this experiment in an empty parking lot). Let's say there is a car coming toward you at 60 miles per hour (mph) and its horn is blaring. You will hear the horn playing one "note" as the car approaches, but when the car passes you the sound of the horn will suddenly shift to a lower note. It's the same horn making the same sound the whole time. The change you hear is caused by Doppler shift.
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HOW RADAR WORKS A radar system, as found on many merchants’ ships, has three main parts: 1. The antenna unit or the scanner 2. The transmitter receiver or ‘transceiver’ and 3. the visual display unit The antenna is two or three meter wide and focuses pulses off very high frequency radio energy into a narrow vertical beam. The frequency of the radio waves is basically about 10,000 Mhz. The antenna is rotated at the rate of 10 to 25 rpm so that radar beam swaps through 300degree Celsius all around the shiout to a range of about 90 kms. In all radar it is vital that the transmitting and the receiving in a transceiver are in close harmony. Every thing depends on accurate measurement of the time that passes between the transmission of pulse and the return of the echo. About 1000, pulses per second are transmitted. Though it is varied to suit the requirements. Short pulses are best for shortrange 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
25
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
26
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 RADAR 2. 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.
RADAR EQUATION The amount of power P r returning to the receiving antenna is given by the radar equation:
where •
•
•
•
P t = transmitter power Gt = gain of the transmitting antenna Ar = effective aperture (area) of the receiving antenna σ = radar cross section, or scattering coefficient, of the target
•
F = pattern propagation factor
•
Rt = distance from the transmitter to the target
•
Rr = distance from the target to the receiver. In the common case where the transmitter and the receiver are at the same location, Rt
= Rr and the term Rt2 Rr 2 can be replaced by R4, where R is the range. This yields:
This shows that the received power declines as the fourth power of the range, which means that the reflected power from distant targets is very, very small. The equation above with F = 1 is a simplification for vacuum without interference. The propagation factor accounts for the effects of multipath and shadowing and depends on the details of the environment. In a real-world situation, pathloss effects should also be considered.
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RADAR SIGNAL PROCESSING Distance measurement
Transit time
Principle of radar distance measurement using pulse round trip time. One way to measure the distance to an object is to transmit a short pulse of radio signal, and measure the time it takes for the reflection to return. The distance is one-half the product of round trip time (because the signal has to travel to the target and then back to the receiver) and the speed of the signal. Range
cτ =
2
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.
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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.
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DIFFERENT TYPES OF RADARS
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) 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
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system consists mainly of an Antenna, Transmitter cabin and Display cabin mounted on three separate vehicles.
SYSTEM CHARACTERISTICS
Range up to 90 km (for fighter aircraft)
Height coverage 35m to 3000m subject to Radar horizon
Probability of detection: 90% (Single scan)
Probability of false alarm: 10E-6
Track While Scan (TWS) for 2D tracking
Capability to handle 200 tracks
Association of primary and secondary targets
Automatic target data transmission to a digital modem/networking of radars
Deployment time of about 60 minutes
FEATURES
Fully coherent system
Frequency agility
Pulse compression
Advanced signal processing using MTD and CFAR Techniques
Track while scan for 2-D tracking
Full tracking capabilities for maneuverings targets
Multicolor PPI Raster Scan Display, presenting both MTI and Synthetic Video
Integral IFF
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3. Tactical Control Radar This is an early warning, alerting and cueing system, including weapon control functions. It is specially designed to be highly mobile and easily transportable, by air as well as on the ground. This radar minimizes mutual interference of tasks of both air defenders and friendly air space users. This will result in an increased effectiveness of the combined combat operations. The command and control capabilities of the RADAR in combination with an effective ground based air Defence provide maximum operational effectiveness with a safe, efficient and flexible use of the airspace.
FEATURES
All weather day and night capability
40 km ranges, giving a large coverage
Multiple target handling and engagement capability
Local threat evaluation and engagement calculations assist the commander's
decision making process, and give effective local fire distribution
Highly mobile system, to be used in all kinds of terrain, with short into and out of action
times (deployment/redeployment)
Clutter suppression
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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.
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RADAR TRANSMITTER 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.
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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 38
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 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
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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 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
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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 Pseudorandomly : 32 point stagger is used for low and high PRF and 64 point stagger is used for 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.
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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
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scan-to-scan and CPI-to-CPI basis is employed to ensure better performance against blind speed conditions. 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.
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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. 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.
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•
SYSTEM TIMING (also contain circuits for internal timing requirements of SP).
•
SYSTEM BITE – Generates control for simulated target generation by Receiver.
•
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.
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Fully 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
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pulses of the transmitter would destroy the receiver if energy were allowed to enter the receiver.
Mixer Stage The function of the mixer stage is to convert the received rf energy to a lower, intermediate frequency (IF) that is easier to amplify and manipulate electronically. The intermediate frequency is usually 30 or 60 megahertz. It is obtained by heterodyning the received signal with a local-oscillator signal in the mixer stage. The mixer stage converts the received signal to the lower IF signal without distorting the data on the received signal.
IF-Amplifier After conversion to the intermediate frequency, the signal is amplified in several IFamplifier 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
47
the Phase Sensitive Detector and also through a frequency divider generates the system PRF in the Synchronizer.
Mixer / Exciter The function of this mixer stage is to convert the StaLO- Frequency and the COHOFrequency 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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MAGNETRON
Figure 1: Magnetron МИ 29Г of the Radar „Bar Lock”
In 1921 Albert Wallace Hull invented the magnetron as a powerful microwawe tube. Magnetrons function as self-excited microwave oscillators. Crossed electron and magnetic fields are used in the magnetron to produce the high-power output required in radar equipment. These multicavity devices may be used in radar transmitters as either pulsed or cw oscillators at frequencies ranging from approximately 600 to 30,000 megahertz. The relatively simple construction has the disadvantage, that the Magnetron usually can work only on a constructively fixed frequency.
Physical construction of a magnetron
The magnetron is classed as a diode because it has no grid. The anode of a magnetron is fabricated into a cylindrical solid copper block. The cathode and filament are at the center of the tube and are supported by the filament leads. The filament leads are large and rigid enough to keep the cathode and filament structure fixed in position. The cathode is indirectly heated and is constructed of a high-emission material. The 8 up to 20 cylindrical holes around 49
cathode
filament leads
pickup loop
its circumference are resonant cavities. The cavities control the output frequency. A narrow slot runs from each cavity into the central portion of the tube dividing the inner structure into as many segments as there are cavities.
Figure 2: Cutaway view of a magnetron The open space between the plate and the cathode is called the interaction space. In this space the electric and magnetic fields interact to exert force upon the electrons. The magnetic field is usually provided by a strong, permanent magnet mounted around the magnetron so that the magnetic field is parallel with the axis of the cathode.
Figure 3: forms of the plate of magnetrons The form of the cavities varies, shown in the Figure 3. The output lead is usually a probe or loop extending into one of the tuned cavities and coupled into a waveguide or coaxial line. a) slot- type b) vane- type c) rising sun- type d) hole-and-slot- type
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Basic Magnetron Operation As when all velocity-modulated tubes the electronic events at the production microwave frequencies at a Magnetron can be subdivided into four phases too: 1. phase: Production and acceleration of an electron beam 2. phase: Velocity-modulation of the electron beam 3. phase: Forming of a „Space-Charge Wheel” 4. phase: Dispense energy to the ac field
Figure 4: the electron path under the influence of the varying magnetic field.
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1. Phase: Production and acceleration of an electron beam When no magnetic field exists, heating the cathode results in a uniform and direct movement of the field from the cathode to the plate (the blue path in figure 4). The permanent magnetic field bends the electron path. If the electron flow reaches the plate, so a large amount of plate current is flowing. If the strength of the magnetic field is increased, the path of the electron will have a sharper bend. Likewise, if the velocity of the electron increases, the field around it increases and the path will bend more sharply. However, when the critical field value is reached, as shown in the figure as a red path, the electrons are deflected away from the plate and the plate current then drops quickly to a very small value. When the field strength is made still greater, the plate current drops to zero.
When the magnetron is adjusted to the cutoff, or critical value of the plate current, and the electrons just fail to reach the plate in their circular motion, it can produce oscillations at microwave frequencies. 2. Phase: Velocity-modulation of the electron beam
The electric field in the magnetron oscillator is a product of ac and dc fields. The dc field extends radially from adjacent anode segments to the cathode. The ac fields, extending between adjacent segments, are shown at an instant of maximum magnitude of one alternation of the rf oscillations occurring in the cavities.
Figure 5: The high-frequency electrical field 52
Well, the electrons which fly toward the anode segments loaded at the moment more In the figure 5 is shown only the assumed high-frequency electrical ac field. This ac field work in addition to the to the permanently available dc field. The ac field of each individual cavity increases or decreases the dc field like shown in the figurepositively are accelerated in addition. These get a higher tangential speed. On the other hand the electrons which fly toward the segments loaded at the moment more negatively are slow down. These get consequently a smaller tangential speed. 3. Phase: Forming of a „Space-Charge Wheel”
On reason the different speeds of the electron groups a velocity modulation appears therefore.
Figure 6: Rotating space-charge wheel in an eight-cavity magnetron The cumulative action of many electrons returning to the cathode while others are moving toward the anode forms a pattern resembling the moving spokes of a wheel known as a „Space-Charge Wheel”, as indicated in figure 6. The space-charge wheel rotates about the cathode at an angular velocity of 2 poles (anode segments) per cycle of the ac field. This phase relationship enables the concentration of electrons to continuously deliver energy to sustain the rf oscillations. One of the spokes just is near an anode segment which is loaded a little more negatively. The electrons are slowed down and pass her energy on to the ac field. This state isn't static, because both the ac- field and the wire wheel permanently circulate. The tangential speed of the electron spokes and the cycle speed of the wave must be brought in agreement so. 4. Phase: Dispense energy to the ac field
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Figure 7: Path of an electron Recall that an electron moving against an E field is accelerated by the field and takes energy from the field. Also, an electron dispense energy to a field and slows down if it is moving in the same direction as the field (positive to negative). The electron spends energy to each cavity as it passes and eventually reaches the anode when its energy is expended. Thus, the electron has helped sustain oscillations because it has taken energy from the dc field and given it to the ac field. This electron describes the path shown in figure 7 over a longer time period looked. By the multiple breaking of the electron the energy of the electron is used optimally. The effectiveness reaches values up to 80%.
Figure 13: Magnetron M5114B of the ATC-radar ASR-910
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Figure 13: Magnetron VMX1090 of the ATC-radar PAR-80 This magnetron is even equipped with the permanent magnets necessary for the work.
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