Pulse radar uses a pulsed microwave signal to determine target range. The round-trip delay time of the pulsed microwave signal is used to determine the target range. The transmit pulse consists of burst of microwave signal with pulse duration of 100 ms to 50 ns. For better resolution shorter pulses are used and for better signal-to-noise ratio longer pulses are desired.

Pulse radar uses pulse repetition frequencies (PRF) ranging from 100 Hz to 100 kHz. High PRF gives more returned pulses per unit time hence performance is improved but lower PRF are used for avoiding range ambiguities.

Transmitter Section

A trigger source generates pulses of appropriate time and frequency which are fed to modulator. The modulator provides rectangular voltage pulses which are used as supply voltage for the output tube.

These rectangular pulses switch on and off the output tube. TI1is output tube may be a magnetron oscillator, travelling wave tube or Klystron amplifier. The high powered output of tube is coupled to antenna by a duplexer.

Function of Duplexer

After transmitting power by transmitter, the echo is produced. As the echo is intercepted by the antenna, duplexer disconnect the transmitter from antenna and connects the receiver to it. The received echo power is amplified and then demodulated.

The radar is able to show the exact target position from the information of azimuth (horizontal) and elevation (vertical) of antenna drive motor.

The distance of the target is calculated by the required to receive the echo pulse after the transmission.

Receiver Section

The receiver section is connected to the antenna by duplexer. The receiver section is super heterodyne type and it consists of mixer, IF amplifier, detector and video amplifier.

The first stage of the receiver is usually an RF amplifier with very low noise properties. The RF amplifier is followed by a mixer of a fairly low noise figure. The mixer is a crystal diode which fed to If amplifier. The If amplifier operates at 30 or 60 MHz or at nearby frequency. IF stage provides most of the receiver gain. The IF amplifier should be a low noise device to ensure that the overall noise figure of the receiver does not deteriorate to a great extent.

The down conversion from microwave frequency to IF frequency may be done in number of stages to ensure adequate image frequency suppression. The detector is a crystal diode, whose output is amplified by video amplifier having the same bandwidth as the IF amplifier, the output signal is then fed to a display unit which may be a CRT.