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Tuesday, 17 September 2019

Radar Block Diagram and Working Principle

Radar Block Diagram and Working Principle

Radar Working Principle:

A transmitter produces an electromagnetic signal that is radiated to the space by an antenna. A part of the transmitted energy is catched by the target and is reradiated in many directions. The radiations directed back towards the radar is collected by the receiving antenna and is delivered to the receiver at the receiver the signal is processed to detect the presence of target and determine its location. A single antenna can act as transmitter and receiver. The range or distance to the target is found out by measuring the time taken by the radar signal to travel to the target and return back to radar.

Block Diagram of Radar:

The transmitter can be a power amplifier such as klystron, travelling wave tube etc. It can also be a power oscillator such as magnetron. The radar signal is produced at low power by a waveform generator which is then amplified by the power amplifier.

The output of the power amplifier is delivered to the antenna by a duplexer which is then radiated into the space. The duplexer allows a single antenna to be used as both transmitter and receiver. Duplexer is a device that produces a short circuit at the input to the receiver when the transmitter is operating so that high power flows to the antenna and not to the receiver. On reception the duplexer directs the echo signal to the receiver and not to the transmitter.

The receiver is always super heterodyne in nature. The input stage is a low noise RF amplifier. The mixer and LO convert the RF Signal to an intermediate frequency which is amplified by the IF amplifier. The IF amplifier is designed as a matched filter, which maximizes the output signal to peak ratio. The matched filter maximizes the detectability of weak echo signals and attenuates unwanted signals. 

The IF amplifier is followed by a detector or demodulator. Its purpose is to extract the modulating signal from the carrier signal. The combination of IF amplifier and detector acts as an envelope detector which transmits the modulating signal and rejects the carrier signal. The signal at the output of detector is amplified by an amplifier to provide sufficient gain to the signal. At the output of the receiver, a decision is made whether or not a target is present if the output is greater than the threshold the decision is that target is present. If the output is less than threshold it is assumed that only noise is present.

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