đź“ŤRadar system
Transmitter:
• The transmitter may be an oscillator, such as a magnetron, that is " pulsed“(turned on and on) by the modulator to generate a repetitive train of pulses.
• The magnetron has probably been the most widely used of the various microwave generators for radar.
• A typical radar with a peak power of the order of a megawatt, an average power of several kilowatts, a pulse width of several microseconds, and a pulse repetition frequency of several hundred pulses per second.
• The waveform generated by the transmitter travels via a transmission line to the antenna, where it is radiated into space. A single antenna is generally used for both transmitting and receiving.
Duplexer:
• The duplexer acts as a rapid switch to protect the receiver from damage when the high-power transmitter is on.
• On reception, with the transmitter off, the duplexer directs the weak received signal to the receiver rather than to the transmitter.
• Duplexers generally are some form of gas-discharge device and may be used with solid-state or gas-discharge receiver protectors.
• The duplexer might consist of two gas-discharge devices, one known as a TR (transmit-receive) and the other an ATR (anti-transmit-receive). The TR protects the receiver during transmission and the ATR directs the echo signal to the receiver during the reception.
• A solid-state circulator as an isolator provides isolation between the transmitter and the receiver.
Receiver
• The receiver is usually of the superheterodyne type.
• The first stage might be a low-noise RF amplifier, such as a parametric amplifier or a low-noise transistor. However, it is not always desirable to employ a low-noise first stage in radar.
• The receiver input can simply be the mixer stage, especially in military radars that must operate in a noisy environment. Although a receiver with a low-noise front-end will be more sensitive, the mixer input can have greater
dynamic range, less susceptibility to overload, and less vulnerability to electronic interference.
• The mixer and local oscillator (LO) converts the RF signal to an
intermediate frequency (IF).
• The IF amplifier should be designed as a matched filter i.e. its frequency-response function H ( f ) should maximize the SNR ratio at the output.
• After maximizing the signal-to-noise ratio in the IF amplifier, the pulse modulation is extracted by the second detector and amplified by the video amplifier to a level where it can be properly displayed, usually on a cathode-ray tube (CRT).
• Timing signals are also supplied to the indicator to provide the range zero. The angle information is obtained from the pointing direction of the antenna.
