Radar is an object-detection system designed for detecting and tracking objects (targets) at considerable distances.The word radar is an acronym derived from the phrase Radio Detection And Ranging.
Principle of operation
A radar system has a transmitter that emits radio waves called radar signals in predetermined directions. When these come into contact with an object they are usually reflected or scattered in many directions. The radar signals that are reflected back towards the transmitter are the desirable ones that make radar work.
Radars transmit directional microwave radio pulses with a rotating ariel (the scanner) in a 360º circle around the machine. It detects the bearing and range of echoing pulse returns from significant surrounding targets to produce a map like display.
Considerable power is required by a radar for transmit mode, of up to 400 watts even in the smaller sets. The supply is usually a small solid state power pack or motor alternator or a generator with larger sets.
Super high frequencies of electromagnetic energy waves (3000 to 10000 MHz, these are wavelengths of 10 and 3 cm, respectively) are produced in the oscillator. The operating cycle of the oscillator is initiated by the trigger, which determines the pulse repetition frequency (PRF). The pulses are shaped in the modulator, which determines the pulse length, then passed to the magnetron, which converts the energy into radio waves and determines the radar frequency. They are then passed to the transmitter, which in modern radars is usually combined with the receiver (the transceiver). The transceiver is usually located within the scanner unit.
The pulses are transmitted to the scanner unit by the waveguide. A waveguide is hollow copper tubing, usually rectangular in cross section, having dimensions according to the wavelength of the carrier frequency. An electronic switch in the waveguide, called the transmit/receive cell (T/R) isolates the receiver during transmission to protect it from the high power of the transmission. In modern radars the waveguide and the T/R switch are usually located within the scanner unit.