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ABSTRACT RADAR (Radio Detection and Ranging) is basically a means of gathering information about distant objects by transmitting electromagnetic waves at them and analyzing the echoes. Radar has been employed on the ground, in air, on the sea and in space. Radar finds a number of applications such as in airport traffic control, military purposes, coastal navigation, meteorology and mapping etc.

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The development of the radar technology took place during the World War II in which it was used for detecting the approaching aircraft and then later for many other purposes which finally led to the development of advanced military radars being used these days. Military radars have a highly specialized design to be highly mobile and easily transportable, by air as well as ground.

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INTRODUCTION   Military radar should be an early warning, altering along with weapon control functions. It is specially designed to be highly mobile and should be such that it can be deployed within minutes. Military 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.

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The command and control capabilities of the radar in combination with an effective ground based air defense provide maximum operational effectiveness with a safe, efficient and flexible use of the air space. The increased operational effectiveness is obtained by combining the advantages of centralized air defense management with decentralized air defense control.

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FUNCTIONAL DESCRIPTION OF RADAR SUBSYSTEM   The detection of air targets is accomplished by the search radar, the video processor and the color PPI unit. The color PPI unit provides the presentation of all moving targets down to very low radial speeds on a PPI screen.

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The search radar is pulse Doppler radar (also called MTI radar) i.e. it is capable of distinguishing between the echo from a fixed target and that of a moving target. The echoes from fixed target are eliminated, so that the echoes from the moving targets are presented on the screen

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Block Diagram

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The main units of radar subsystem are: - 1. HT Unit The high tension unit converts the phase mains voltage into a DC supply voltage of about in the order of kV for the transmitter unit 2. Transmitter Unit The transmitter unit comprises: Modulator The modulator consists of the following components: -  Start Pulse Amplifier  Pulse Unit

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b) Magnetron The magnetron is a self-oscillating RF power generator. It is supplied by the modulator by high voltage pulses, whereupon it produces band pulses

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3) LO+AFC Unit: The LO+AFC unit determines the frequency of the transmitted radar pulses. It comprises Of: - Lock pulse mixer AFC discriminator Solid State Local Oscillator (SSLO) Coherent Oscillator (COHO)

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4) Receiver Unit The receiver unit converts the received RF echo signals to IF level and detects the IF signals. By detecting the IF signals in two different ways, two receiver channels are obtained called MTI channel and linear channel The RF signals received by radar antenna are applied to the low noise amplifier.

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5) Antenna: The search antenna is a parabolic reflector, rotating with a high speed. In the focus of the reflector is a radiator, which emits the RF pulses, and which receives the RF echo pulses. In the waveguide is the polarization shifter, which causes the polarization of the RF energy to be either horizontally or circularly.

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6) Video processor The video processor processes the MTI video from the MTI receiver channel, to make the video suitable for the presentation on the colour PPI screen.   7) Protection Units There are some protection units such as arc sensor to protect the magnetron against arcing and RF power sensor maintaining the RF power.

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OPERATING THE RADAR:  The operator’s main task is to watch the PPI (Plan Position Indicator) display, which presents only moving targets in the normal mode (MTI-MODE). Detected target can be assigned with the joystick controlled order marker to initiate target tracking. Target tracking is started and a track marker appears over the target echo. A label is displayed near the track marker. The system computer in the processor unit processes data on this tracked target. When an aircraft does not respond to the IFF interrogation it is considered to be unknown.

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ADVANCED FEATURES AND BENEFITS   Typical military radar has the following advanced features and benefits: -    All-weather day and night capability.  Multiple target handling and engagement capability.  Short and fast reaction time between target detection and ready to fire moment.  Easy to operate and hence low manning requirements and stress reduction under severe conditions.  Highly mobile system, to be used in all kind of terrain  Flexible weapon integration, and unlimited number of single air defence weapons can be provided with target data.

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DISADVANTAGES: Time - Radar can take up to 2 seconds to lock on Radar has wide beam spread (50 ft diameter over 200 ft range). Cannot track if deceleration is greater than one mph/second. Large targets close to radar can saturate receiver. Hand-held modulation can falsify readings.

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CONCLUSION: Military radars are one of the most important requirements during the wartime, which can be used for early detection of ballistic missile and also for accurate target detection and firing. Radar system discussed here has a built in threat evaluation program which automatically puts the target in a threat sequence, and advises the weapon crew which target can be engaged first.

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REFERENCES: 1) Skolnik ‘Introduction to Radar Systems’ McGraw Hill 2) ‘Electronic Communication Systems’ by Kennedy, Davis Fourth Edition 3) Bharat Electronics Limited website 4) Various other internet sites and journals

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