AAI

INDUSTRIAL TRAINING

DATE: 8TH JUNE TO 3RD JULYBATCH: 1

INDEX1. AAI2. VHF

(a) Introduction(b) VHF Transmitter/ Receiver(b) Dipole Antenna(c) VCCS (Voice Communication Control System)(d) RCAG (Remote Control Air to Ground)(e) DATIS (Digital Airport Terminal Information Service)(f) RECORDER

3. AMSS

(a) Introduction(b) Major areas of AMSS(c) Categories of Messages(d) Address indicator of AFTN messages(e) Block diagram of AMSS (f) ODBC

4. RADAR

(c) Introduction(d) Use(e) Principle(f) Types(g) L- Band Radar

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AIRPORT AUTHORITY OF INDIA

The Airports Authority of India (AAI) under the Ministry of Civil Aviation is responsible for creating, upgrading, maintaining and managing civil aviation infrastructure in India. It provides Air traffic management (ATM) services over Indian airspace and adjoining oceanic areas. It also manages a total of 125 Airports, including 11 International Airports, 8 Customs Airports, 81 Domestic Airports and 25 Civil enclaves at Military Airfields.

FUNCTIONS

Design, Development, Operation and Maintenance of international and domestic airports and civil enclaves.

Control and Management of the Indian airspace extending beyond the territorial limits of the country, as accepted by ICAO.

Construction, Modification and Management of passenger terminals. Development and Management of cargo terminals at international and domestic airports. Provision of passenger facilities and information system at the passenger terminals at

airports. Expansion and strengthening of operation area, viz. Runways, Aprons, Taxiway etc. Provision of visual aids. Provision of Communication and Navigation aids, viz. ILS, DVOR, DME, Radar etc.

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VERY HIGH FREQUENCY (VHF)

INTRODUCTION

VHF FREQUENCY RANGE - (117.975 - 136.975) MHz

USERS - ATCO (Air Traffic Controllers), Airlines/Defense Pilots.

The VHF unit of Airports Authority of India provides for the following functions-

- Maintain all VHF channel.- Providing radio communication between ATCO and Aircraft. - Additional standalone system is provided through J -Controller and Transceivers at different ATC positions.- Serviceability of Mains and Standby equipment 99·9%· - All preventive and corrective maintenance schedules are performed. - The air-to-ground communications are also recorded. Analysis of recorded communication is done by DGCA, AAI, ATC personnel for the purpose of investigation in case of accident/incidence.

FACILITIES/COMPONENTS AVAILABLE WITH VHF UNIT

VHF Tx, Rx, and J -Controller /Tran receiver. RCAG (Remote controlled Air to Ground) DATIS (Digital Airport Terminal Information Services) VCS (IeS 200/60) Dipole antenna Integrated Communication System for Air Traffic Control Recording Facilities - DVTR (Digital Voice Tape Recorder) - MVLR (Meltron Voice Tape Recorder)- Ricochet (Digital Voice Tape Recorder) • HF (High Frequency) Communication

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VHF TRANMITTER /RECIEVER

The VHF Tx /Rx work on Amplitude Modulation principle. There are three transmitter/receivers used in the VHF unit- those made by ECIL, PAE and OTE.

MAKE ECIL PAE OTE MODEL NO. OF Tx 5350 T6T DT100

MODEL NO. OF Rx 5100 T6R DR100

About Tx 5350:

The Electronics Corporation of India Limited (ECIL) / Park Air Electronics (PAE) type 5350 single channel transmitters are designed for the transmission of amplitude modulated signals within VHF aeronautical frequency band. The transmitter is intended for use in ground station environments and can be combined with an associated EClL / PAE receiver to form a transmitter / receiver system. The standard transmitter operates in the frequency range 118 to 136.975 MHz, with 25 kHz channel spacing. The frequency range of the 5350 transmitters can be extended to operate between 108 and 155.975 MHz.

The Transmitter consists of six PCBs / modules-

Synthesizer module Audio & Control module RF PA module Filter / Coupler assembly Power supply module PSU regulation module

Function of various modules of VHF Tx 5350 is given below.

Synthesizer Module: The Synthesizer module produces the transmitter's carrier frequency, which is used as the RF drive to the RF PA module. The RF drive output is enabled only when the transmitter is keyed. The synthesizer's carrier frequency output is derived form a 6 MHz Temperature Compensated Crystal Oscillator (TCXO) which provides frequency stability of 1.5 ppm (parts per million).

Audio and Control Module: - The audio and control module processes the transmitter's speech and data inputs to provide a modulation signal for the RF PA module. The module contains audio circuits, transmitter control circuits and BIT control circuits.

RF PA Module: - The RF PA module provides the drive and power amplification necessary to produce the 50 watt transmitter output. The module is supplied with two inputs i.e., carrier frequency from the Synthesizer, and the modulation signal from the Audio and Control module.

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Filter / Coupler Assembly: - The filter / coupler assembly contains a low-pass filter to remove unwanted RF components, and a directional coupler to detect the forward and reflected power levels.

Power Supply Module: - The Power Supply Module provides an unregulated supply between 21.4 V and 32 V DC from the mains AC supply of220V.

Power Supply Regulation Module: - The PSU regulation module is supplied with the un-regulated supply from the PSU module as one input and 28 V (Nominal) DC supply from the battery backup as the second input and provides the following outputs.

A + 15 V regulated supply for the Synthesizer Module, and the Audio & Control Module. B. + 10 V and + 5 V regulated supplies for the Audio & Control Module. C. + 21.4 to 32 V unregulated supply for the RF PA Module, Audio and Control Module and front panel indicators.

All these output voltages are generated from internal regulator ICs. When both AC and DC supplies are connected, an automatic changeover to DC is initiated on the loss of the AC supply. When both supplies are connected, priority of operation is from the AC supply.

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DIPOLE ANTENNA

A dipole antenna is an antenna that can be made by a simple wire, with a centre-fed driven element for transmitting or receiving radio frequency energy. These antennas are the simplest practical antennas from a theoretical point of view; the current amplitude on such an antenna decreases uniformly from maximum at the centre to zero at the ends.

FOLDED DIPOLE ANTENNA

The tips of the antenna are folded back until they almost meet at the feed point, such that the antenna comprises one entire wavelength. This arrangement has a greater bandwidth than a standard half wave dipole. If the conductor has a constant radius and cross-section, at resonance the input impedance is four times that of a half-wave dipole

STACKED DIPOLE ANTENNA

We stack dipoles in order to increase the gain over that obtainable from one dipoles and/or to decrease the beam width. The increase in gain is due to the reduction in beam width and it should be noted that the beamwidth is reduced in the plane of stacking only. If we stack vertically the beamwidth is decreased in the vertical or "H" plane of a horizontally polarised dipole. Stacking horizontally results in a narrower beamwidth in the horizontal or "E "plane of a horizontally polarised dipole. In some applications, such as interference from or to points off to one side or below the main lobe, the reduction in beam width is a more important consideration than the gain increase. However mostly with stack to get more gain.

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VCCS (Voice Communication Control System)

Features:

Upto 700 radio and telephone interface and upto 200 operator positions VCCS used is ICS200/60 Two VCCS systems are used-one online and other standby.

It has the following parts-

Communication Server Communication Controller Interface Cards Operator Position Management Server

The Integrated Communications System ICS 200/60 uses the most advanced digital technology based on the standard 2 Mbps Ei, including powerful microprocessors, digital signal processors and fast, nonblocking switching components.

The ICS 200/60 has a fully digital design and provides distributed intelligence on the server and operator positions. Thus fast switching performance for radio and telephone channels as well as a high availability with smooth degradation in case of eventual failures is achieved.

The four main elements of the system are:

The analogue interface modules for radio, all types of telephone applications (LB, CB, PSTN ... ) and the digital interfaces (e.g. Leased Line)! Each interface module connects for redundancy reasons through a 2 Mbps Ei main and a standby bus to the server system. The intelligent operator positions with integrated voice switching and signal processing, located in one or more dual 2 Mbps Ei rings with redundant design.

The server systems (usually in a redundant configuration) act as a cross connects between the interface bus and the ring of the operator positions. The management position is present to monitor, control and, configure the system.

A separate communication path is reserved for configuration and system management: the Ethernet LAN. It is used for the transmission of configuration data, event logs as well as for the program and data download into the server system. Multiple management positions as well.

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RCAG (REMOTE CONTROL AIR TO GROUND)

Function is to provide extended range of VHF communication Control site consist of single equipment fitted with voting unit and band signaling unit configured to control one two, three or four radio sites.

Two type RCAG used:

1. RCAG-ECIL

Local site- Delhi Remote site- Khajuraho Frequency - 120.000 Mhz Used for area control centre (east) Media-VSAT or OFC VSAT-provided by heel OFC-provided by mtnl/bsnl

2. RCAG- PARK AIR SYSTEM

Local site-Delhi Remote site 1. Amritsar 2. Jodhpur 3. Sundar Nagar Frequency-124.55 MHz Used for area control centre (west) Media - OFC (optical fiber communication) and DSCN( dedicated satellite communication network) OFC - provaided by mtnl / bsnl DSCN - maintained by AAI

DATIS (Data-link Airport Terminal Information Service)

Function - It provides all Terminal information to the Aircraft at regular interval. It is a software-based system.

The current and real-time aeronautical information is essential for aircraft’s operation and air Navigation, particularly the meteorological information and active NOTAMs in the approach and landing phases. They are also important for the coordination and development of air services. One of the systems providing this type of service to aircraft is the ATIS systems (Automatic Terminal Information Service).

DATIS is a transcribed, digitally transmitted version of the ATIS audio broadcast, usually accessed from a digital display. DATIS may be incorporated into the core ATIS system, or be realized as a separate system with a data interface between voice ATIS and DATIS

The DATIS transmissions are used at airports to notify the landing and take-off aircrafts regarding current local atmospheric conditions, runway conditions, communication frequencies and any other important information. These transmissions are updated each time when meteorological or runway conditions changes. The ATIS transmissions are used by most of the airports, the operation frequency could be found in the aeronautical charts close

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to the airport symbol. If there is an ATIS system, the operation frequency is close to the word ATIS.

Data link-automatic terminal information service is a continuous broadcast of recorded noncontrol information in busier terminal (i.e. airport) areas.D ATIS broadcasts contain essential information, such as weather information, which runways are active, available approaches, and any other information required by the pilots, such as important NOTAMs. Pilots usually listen to an available DATIS broadcast before contacting the local control unit, in order to reduce the controllers' workload and relieve frequency congestion.

The recording is updated when there is a significant change in the information, like a change in the active runway. It is given a letter designation (e.g. bravo), from the ICAO spelling alphabet. The letter progresses down the alphabet with every update and starts at Alpha after a break in service of 12 hours or more. When contacting the local control unit, a pilot will indicate he/she has "information" and the ATIS identification letter to let the controller know that the pilot is up to date with all current information.

Data link-automatic terminal information service (D-ATIS). The provision of ATIS via data link.

Frequency - 126.4 MHz This equipment has two parts-1. Control Equipment - Location - Equipment Room along with Tx/ Rx. - Transmitter located at Remote RX and Tx station Bijwasan broadcast by one Tx at a time. - Media - UHF Link for Bijwasan - Two wire line for Remote Rx 2. Operator interface - Location - Tower - DATIS Data is updated by ATM at regular intervals.

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RECORDER:

Recording and storage of all voice communications is a basic requirement for air traffic control units. The requirement applies to all communication, i.e. ground-ground communications (G/G) and air-ground communications (A/G). The G/G is the communications among air traffic control units or centers where as the A/G communication is between air traffic controllers and pilots.

Recording facilities shall be provided on all voice communication channels. Each station is provided with multi channel voice recording systems (analog/digital) for recording of channels which includes operational voice communications on all ATS channels and all important telephones and intercoms.In vhf two recorders are used one is of RETIA and another is of RICOCHET company.

RETIA

Retia is a type of reorder which is designed to store any type of data source.In Retia 128 and 64 channels are available. Retia works on unix operating system.

RICOCHET

Ricochet is a modular system capable of being expanded and interfaced with a variety of data source. Ricochet is designed to be adaptable to virtually any type of data source. Other than audio recording, the system can record RADAR data and CCTV images. In Ricochet 64 channels are available. Ricochet works on window XP.

RECORDING OF SURVEILLANCE DATA

Surveillance data from Primary and Secondary radar equipment provided at different airports shall be recorded automatically and continuously in the hard disc of computer. It is required that back-up of the recorded data files be taken every day for retention.

The surveillance data from primary and secondary radar equipment used as an aid to air traffic services shall be automatically recorded for use in accident and incident investigations, search and rescue, air traffic control and surveillance systems evaluation and training.

Automatic recording shall be retained for a period of at least thirty days. When the recordings are pertinent to accident and/or incident investigations, they shall be retained for longer periods until no longer required.

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TRANSMITTER

Carrier oscillator-The carrier oscillator generates the carrier signal, which lies in the RF range. The frequency of the carrier is always very high because it is very difficult to generate high frequency with good frequency stability, the carrier oscillator generate a sub multiple with the required carried frequency. This sub multiple frequency is multiplied by the frequency multiplier stage to get the required carrier frequency.

Buffer Amplifier-The purpose of the buffer amplifier is twofold.

a) It first matches the output impedance of the carrier oscillator with the input impedance of frequency multiplier.

b) This is required so that the multiplier does not draw a large current from the carrier oscillator. If this occurs, the frequency of the carrier oscillator will not remain stable.

Frequency Multiplier- This stage is also known as harmonic generator. The frequency multiplier generates higher harmonics of carrier oscillator frequency.

Power Amplifier- The power of the carrier signal is then amplified in the power amplifier stage. This is the basic requirement of a high-level transmitter.

Class C power amplifier-It gives high power current pulses of the carrier signal at its

Output.

Audio driver amplifier-The audio signal to be transmitted is obtained from the microphone. The audio driver amplifier amplifies the voltage of this signal. This amplification is necessary to drive the audio of this signal.

Audio power amplifier- class A or a class B power amplifier amplifies the power of audio signal.

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RECIEVER

RF Amplifier-This provides amplification for the signal as soon as it arrives from the antenna. The amplified signal is then passed to the mixer.

Mixer- The purpose of the mixer is to translate the frequency of the incoming signal to the intermediate frequency.

I.F.Amplifier- I.F amplifier where most of the amplification in a receiver takes place.

Demodulator-From the IF stages, the signal passes to a detector. Here demodulation of the radio-frequency signal takes place to produce an audio signal.

Audio Amplifier- output of detector is amplified and then it goes to speaker.

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AUTOMATIC MESSAGE SWITCHING SYSTEM

INTRODUCTION

The process of getting an aircraft safely and efficiently to its destination depends largely on an efficient communication system besides navigation and surveillance systems. The communication system must be able to provide an accurate and speedy exchange of Aeronautical Information between stations to enable them to control the air space and movement of air traffic to ensure highest standards of safety and quality in air traffic services.

In earlier days of Civil Aviation, the aircrafts were slow moving and hence communication links by means of wireless telegraphy circuits and manual tele‐typewriter circuits, generally known as Aeronautical Fixed Circuit were able to provide Aeronautical Fixed Service (AFS) between two fixed points.

With the advent of high speed aircrafts, increasing number of flight in the airspace across the continent, it was the need of that time to form a Global network of aeronautical fixed circuits for the exchange of messages and/or digital data between aeronautical fixed stations. The concept of Aeronautical Fixed Telecommunication Network (AFTN) was introduced.

India plays a key role in the international AFTN, bridging the gap between the eastern and western parts of the world. Messages originating in the western countries are routed through India to the eastern countries and vice‐versa.

In order to meet the growing demand for air traffic across the air space, India was needed to upgrade and update the communication facilities like AFTN. The Automatic Message Switching System (AMSS) was introduced in India in the year 1986‐87 in two major stations Mumbai and Delhi. As on date, 18 major stations are having ECIL AMSS and other non‐AMSS stations are connected with AMSS station over dialup circuit or working as remote client of AMSS, known as RWS.

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MAJOR AREAS OF AMSS:

a) System:

AMSS is a dual architecture computer based system consisting of few servers and workstations which are linked with each other over a local area network as well as with other equipments/ devices for data communication.

b) Messages:

AMSS is mainly for exchange of AFTN messages, but at the same time AMSS can handle some Non‐AFTN messages like AMS messages (formally known as HFRT/Radio Messages).

c) Switching:

AMSS receives the messages from terminals directly connected to it and terminals connected via other switches, and after analysis, it stores the messages and automatically routes the messages to its destination(s). During the above process it uses switching system, which allows on demand basis the connection of any combination of source and sink stations.

AFTN switching system can be classified into 3(three) major categories –

Line switchingMessage switchingPacket switching

d) Automation:

So far automation is concerned for any system, it could be achieved by means of mechanical devices like relay etc and/or application software designed as per requirement. In ECIL AMSS, maximum features of automation like message switching, analyzing, storing, periodical statistics etc are taken care by AMSS software and few by means of mechanical system.

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CATEGORIES OF MESSAGE

The following categories of messages shall be handled by the AFTN:

a) Distress messages b) Urgency messages c) Flight Safety Messagesd) Meteorological Messages e) Flight Regularity Messagesf) Aeronautical Information Service Messagesg) Aeronautical Administrative services messages

Priority of Messages:Depending on the category of messages/type of messages, each message carry a priority Indicator (viz SS, DD, FF, GG, KK) to indicate the priority classification for transmission/handling over AFTN.‘SS’ is the top most priority, then ‘DD’ & ‘FF’, and ‘GG’ / ‘KK’ are the lowest priority of messages.

DISTRESS MESSAGES (Priority Indicator SS)This message category shall comprise those messages sent by mobile stations reporting grave and imminent danger and all other messages relating to the immediate assistance required by the mobile station in distress threaten them.

URGENCY MESSAGES: (Priority indicator DD)This category of messages shall comprise messages concerning the safety of ship, aircraft, or other vehicles, or of some person on board or within sight.

FLIGHT SAFETY MESSAGES. (Priority indicator FF)• Movement and control messages • Messages originated by aircraft operating agency of immediate concern to an aircraft in flight or about to depart.

METEOROLOGICAL MESSAGES (priority indicator GG)• Messages concerning forecast e.g. terminal aerodrome forecasts (TAFs), area and route forecasts.• Messages concerning observations and reports e.g. METAR, SPECI.

FLIGHT REGULARITY MESSAGES (Priority indicator‐GG)• Aircraft load messages.• Messages concerning change in aircraft operating schedule.• Messages concerning aircraft servicing.• Messages concerning changes in collective requirement of passengers, crew and cargo covered by deviation from normal operating schedule.

AERONAUTICAL ADMINISTRATIVE MESSAGES• Operation and maintenance of facilities essential for safety or regularity of aircraft operation.• Essential to efficient functioning of aeronautical telecommunication service.• Exchanged between government civil aviation authorities relating to aircraft operation.

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ADDRESSEE INDICATOR of AFTN Messages

Each AFTN message has two address information:• Who has originated the message (Source)• To whom it is addressed or to whom it will be distributed (Sink)In order to maintain uniformity, pattern and ease for routing of messages, an 8(eight)‐letter code group, known as addressee indicator, are formulated .Addressee Indicator has two parts: first 4 letter code groups is assigned to a location of an aeronautical fixed station and next 4 letters code group to identify the addressee (Organisation/unit/ person addressed) of that station.

LOCATION INDICATOR (L.I.)

Four letter location indicator formulated and assigned to a geographical location where there is situated a station forming a part of aeronautical fixed service.

FORMATION OF LOCATION INDICATOR

The world is divided into 22 non‐over‐lapping AFS routing areas, each of which is assigned a separate identifying letter from A to Z excluding letters I, J, Q and X.

a) Assignment of the first letter of a location indicator:

The first letter of the location indicator shall be the letter assigned to the AFS routing area within which the location is situated except that where the location is served only by a single communication centre situated in another AFS routing area, the first letter shall be that assigned to the area in which that communication centre is situated.

Example: 1st letter of L.I. of Delhi, Kolkata, Nagpur etc, are ‘V’

b) Assignment of the second letter of a location indicator:

Each separate state or territory is assigned a separate identifying letter to permit differentiation between that state or territory and other states or territories in the same AFS routing areas.

Example: Bangkok and Kathmandu both comes under the same AFS routing area ‘V’, they have been allotted separate letter ‘T’ and ‘N’ respectively to differentiate the states.

Hence, the second letter of the location indicator shall be letter assigned to the state or territory (or portion thereof) within which the location is situated, except that where the location is served.

Example : Delhi : VI Mumbai : VA Chennai : VO Kolkata : VE

c) Assignment of the third and fourth letter of a location indicator:The state concerned shall assign the 3rd and 4th letters, as desired in such a way that the 4‐lettercode group location indicator is unique.

Example: VAAU : L.I. of Aurangabad (AU), Western part (A) of India (V).

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BLOCK DIAGRAM OF AMSS

BLOCK DIAGRAM OF AMSS TRANSMISSION

In AMSS two types of media are used:

a) Lease line networkb) Dial up media

Switch are of two types:

a) Managedb) Unmanaged

SERVER:

In AMSS two types of servers are used one is ONLINE server another is HSB(hot standby). Online server is mainly used. If online server is not in working condition then automatically HSB connects to main line.

Four types of data base server:

a) JK-Ab) JK-Bc) JK-Cd) JK-D

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JK-A & JK-B servers are used for NOTAM related message. While JK-C & JK-D are used for flight related message.

Common servers are of two types:

a) TCP/IP- Based on internet protocol addressb) X.25-In this ICON CARD are used for copy messages.

An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication.

An IP address serves two principal functions:

a) Host or network interface identification and location addressing.

b) An address indicates where it is. A route indicates how to get there.

I.P. address classification:

a) Class A: Address range lies between 1.0.0.0 to126.255.255.255. Number of hosts are 4,000,000.Bits in network I.D is 8.

b) Class B: Address range lies between 128.0.0.0 to191.255.255.255 Number of hosts are 65,536.Bits in network I.D is 16.

c) Class C: Address range lies between 192.0.0.0 to223.255.255.255 Number of hosts are 65,536.Bits in network I.D is 24.

d) Class D: Address range lies between 224.0.0.0 to239.255.255.255 Number of hosts are268,400,000.Bits in network I.D is 0.class D used for test only.

e) Class E addresses are reserved for future.

ODBC

In computing, ODBC (Open Database Connectivity) is a standard programming language middleware API for accessing database management systems (DBMS). The designers of ODBC aimed to make it independent of database systems and operating systems. An application written using ODBC can be ported to other platforms, both on the client and server side, with few changes to the data access code.

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RADAR

INTRODUCTION

Radar is an object-detection system that uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish (or antenna) transmits pulses of radio waves or microwaves that bounce off any object in their path. The object returns a tiny part of the wave's energy to a dish or antenna that is usually located at the same site as the transmitter.

Radar was secretly developed by several nations before and during World War II. The term RADAR was coined in 1940 by the United States Navy as an acronym for RAdio Detection And Ranging. The term radar has since entered English and other languages as a common noun, losing all capitalization.

USE

The modern uses of radar are highly diverse, including air and terrestrial traffic control, radar astronomy, air-defense systems, antimissile systems; marine radars to locate landmarks and other ships; aircraft anticollision systems; ocean surveillance systems, outer space surveillance and rendezvous systems; meteorological precipitation monitoring; altimetry and flight control systems; guided missile target locating systems; and ground-penetrating radar for geological observations. High tech radar systems are associated with digital signal processing and are capable of extracting useful information from very high noise levels.

Other systems similar to radar make use of other parts of the electromagnetic spectrum. One example is "lidar", which uses ultraviolet, visible, or near infrared light from lasers rather than radio waves.

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PRINCIPLE

The Primary Radar is based on the principle of echo. The implementation and operation of primary radars systems involve a wide range of disciplines such as building works, heavy mechanical and electrical engineering, high power microwave engineering, and advanced high speed signal and data processing techniques. Some laws of nature have a greater importance here.Radar measurement of range, or distance, is made possible because of the properties of radiated electromagnetic energy.

1. Reflection of electromagnetic wavesThe electromagnetic waves are reflected if they meet an electrically leading surface. If these reflected waves are received again at the place of their origin, then that means an obstacle is in the propagation direction. 

2. Electromagnetic energy travels through air at a constant speed, at approximately the speed of light,

300,000 kilometers per second or 186,000 statute miles per second or 162,000 nautical miles per second.

This constant speed allows the determination of the distance between the reflecting objects (airplanes, ships or cars) and the radar site by measuring the running time of the transmitted pulses. 

3. This energy normally travels through space in a straight line, and will vary only slightly because of atmospheric and weather conditions. By using of special radar antennas this energy can be focused into a desired direction. Thus the direction of the reflecting objects can be measured.

RADAR EQUATION

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

where

Pt = transmitter power Gt = gain of the transmitting antenna Ar = effective aperture (area) of the receiving antenna (most of the time noted as Gr) 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 Rr² can be replaced by R4, where R is the range. This yields:

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DOPPLER EFFECT

Frequency shift is caused by motion that changes the number of wavelengths between the reflector and the radar. That can degrade or enhance radar performance depending upon how that affects the detection process.

This produces information about target velocity during the detection process. This also allows small objects to be detected in an environment containing much larger nearby slow moving objects.

Doppler shift depends upon whether the radar configuration is active or passive. Active radar transmits a signal that is reflected back to the receiver. Passive radar depends upon the object sending a signal to the receiver.

The Doppler frequency shift for active radar is as follows, where   is Doppler frequency,   is transmit frequency,   is radial velocity, and   is the speed of light:

Passive radar is applicable to electronic countermeasures and radio astronomy as follows:

Only the radial component of the speed is relevant. When the reflector is moving at right angle to the radar beam, it has no relative velocity. Vehicles and weather moving parallel to the radar beam produce the maximum Doppler frequency shift.

Doppler measurement is reliable only if the sampling rate exceeds the Nyquist frequency for the frequency shift produced by radial motion. As an example, Doppler weather radar with a pulse rate of 2 kHz and transmit frequency of 1 GHz can reliably measure weather up to 150 m/s (340 mph), but cannot reliably determine radial velocity of aircraft moving 1,000 m/s (2,200 mph).

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TYPES

RADAR can be classified as follows-

1. Depending upon the waveforma. Pulse Radar

Pulse radar sets transmit a high-frequency impulse signal of high power. After this impulse signal, a longer break follows in which the echoes can be received, before a new transmitted signal is sent out. Direction, distance and sometimes if necessary the height or altitude of the target can be determined from the measured antenna position and propagation time of the pulse-signal. One pulse is of 1µs and another of 100µs.

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

2. Depending upon the Principlea. Primary Radar

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

Echo-based (that may generate clutter)

Target Role: Passive

Transfer Power Required: Maximum

Generally used for range detection

Unable to identify the target info

The output power is inversely proportional to the four times of range:

P ∞ 1R4

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

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Interrogator-Transponder based

Target Role: Active

Transfer Power Required: Minimum

Able to identify the target info including altitude, identification code, and other details.

SSR has several modes of operation-

Mode A: In this mode the aircraft's transponder provides positive aircraft identification by transmitting a four-digit code to the ground station. The code system is octal; that is, each of the code digits may be any of the numbers 0-7. There are thus 4096 possible four-digit codes (e.g. 3472).

Mode C: In this mode the aircraft's altitude, derived from on-board instruments, is transmitted to the ground station in addition to the identity.

3. Depending upon the usea. Military Radarb. Aviation Radar c. Marine Radard. Meteorologists Radarse. Police forces use radar guns to monitor vehicle speeds on the roads

4. Depending upon the band

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L BAND RADAR

L band, as defined by the IEEE, is the 1 to 2 GHz range of the radio spectrum.

Wavelength Range: 15-30 cm

Frequency Range: 1-2 GHz

Fig: Simplified Block Diagram for Radar Transmitter and Receiver

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Limiting Factors

Beam Path and RangeThe radar beam would follow a linear path in vacuum, but it really follows a somewhat curved path in the atmosphere because of the variation of the refractive index of air, that is called the radar horizon. Even when the beam is emitted parallel to the ground, it will rise above it as the Earth curvature sinks below the horizon. Furthermore, the signal is attenuated by the medium it crosses, and the beam disperses.The maximum range of conventional radar can be limited by a number of factors:

Line of sight, which depends on height above ground. This means without a direct line of sight the path of the beam is blocked.

The maximum non-ambiguous range, which is determined by the pulse repetition frequency. The maximum non-ambiguous range is the distance between the pulses could travel and return before the next pulse is emitted.

Radar sensitivity and power of the return signal as computed in the radar equation. This includes factors such as environmental conditions and the size (or radar cross section) of the target.

NoiseSignal noise is an internal source of random variations in the signal, which is generated by all electronic components.Reflected signals decline rapidly as distance increases, so noise introduces a radar range limitation. Reflectors that are too far away produce too little signal to exceed the noise floor and cannot be detected. Detection requires a signal that exceeds the noise floor by at least the signal to noise ratio. Noise figure is a measure of the noise produced by a receiver compared to an ideal receiver, and this needs to be minimized.

InterferenceRadar systems must overcome unwanted signals in order to focus only on the actual targets of interest. These unwanted signals may originate from internal and external sources, both passive and active. The ability of the radar system to overcome these unwanted signals defines its signal-to-noise ratio (SNR). The higher a system's SNR, the better it is in isolating actual targets from the surrounding noise signals.

ClutterClutter refers to radio frequency (RF) echoes returned from targets which are uninteresting to the radar operators. Such targets include natural objects such as ground, sea, precipitation (such as rain, snow or hail), sand storms, animals (especially birds), atmospheric turbulence, and other atmospheric effects. Clutter may also be returned from man-made objects such as buildings and, intentionally, by radar countermeasures such as chaff.

Some clutter may also be caused by a long radar waveguide between the radar transceiver and the antenna. In a typical plan position indicator (PPI) radar with a rotating antenna, this will usually be seen as a "sun" or "sunburst" in the centre of the display as the receiver

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responds to echoes from dust particles and misguided RF in the waveguide. AClutter is considered a passive interference source, since it only appears in response to radar signals sent by the radar.

Clutter is detected and neutralized in several ways. Other methods attempt to increase the signal-to-clutter ratio. Clutter moves with the wind or is stationary. Two common strategies to improve measure or performance in a clutter environment are:

Moving Target Indication, which integrates successive pulses and Doppler processing, that uses filters to separate clutter from desirable signals.

Constant False Alarm Rate, a form of Automatic Gain Control (AGC), is a method that relies on clutter returns far outnumbering echoes from targets of interest. The receiver's gain is automatically adjusted to maintain a constant level of overall visible clutter. While this does not help detect targets masked by stronger surrounding clutter, it does help to distinguish strong target sources. In the past, radar AGC was electronically controlled and affected the gain of the entire radar receiver. As radars evolved, AGC became computer-software controlled and affected the gain with greater granularity in specific detection cells.

Fig: Radar multipath echoes from a target cause ghosts to appear.

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Radar Engineering Details

Fig: Radar components

Radar’s components are:

A transmitter that generates the radio signal with an oscillator such as a klystron or a magnetron and controls its duration by a modulator.

A waveguide that links the transmitter and the antenna. A duplexer that serves as a switch between the antenna and the transmitter or the

receiver for the signal when the antenna is used in both situations. A receiver. Knowing the shape of the desired received signal (a pulse), an optimal

receiver can be designed using a matched filter. A display processor to produce signals for human readable output devices. An electronic section that controls all those devices and the antenna to perform the

radar scan ordered by software. A link to end user devices and displays.

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Antenna DesignRadio signals broadcast from a single antenna will spread out in all directions, and likewise a single antenna will receive signals equally from all directions. This leaves the radar with the problem of deciding where the target object is located.

Early systems tended to use omnidirectional broadcast antennas, with directional receiver antennas which were pointed in various directions. For instance, the first system to be deployed, Chain Home, used two straight antennas at right angles for reception, each on a different display. The maximum return would be detected with an antenna at right angles to the target, and a minimum with the antenna pointed directly at it (end on). The operator could determine the direction to a target by rotating the antenna so one display showed a maximum while the other showed a minimum. One serious limitation with this type of solution is that the broadcast is sent out in all directions, so the amount of energy in the direction being examined is a small part of that transmitted. To get a reasonable amount of power on the "target", the transmitting aerial should also be directional.

Fig: Long-range radar antenna, used to track space objects and ballistic missiles.

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Fig: Radar of the type used for detection of aircraft. It rotates steadily, sweeping the airspace with a narrow beam.

Parabolic ReflectorMore modern systems use a steerable parabolic "dish" to create a tight broadcast beam, typically using the same dish as the receiver. Such systems often combine two radar frequencies in the same antenna in order to allow automatic steering, or radar lock.

Types of Scan Primary Scan: A scanning technique where the main antenna aerial is moved to

produce a scanning beam, examples includes circular scan, sector scan, etc. Secondary Scan: A scanning technique where the antenna feed is moved to produce a

scanning beam, examples include conical scan, unidirectional sector scan, lobe switching, etc.

Palmer Scan: A scanning technique that produces a scanning beam by moving the main antenna and its feed. A Palmer Scan is a combination of a Primary Scan and a Secondary Scan.

Conical scanning: The radar beam is rotated in a small circle around the "boresight" axis, which is pointed at the target.

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