working principle of RADAR

A radar system has atransmitterthat emitsradio wavescalledradar signalsin predetermined directions. When these come into contact with an object they are usuallyreflected orscatteredin many directions. Radar signals are reflected especially well by materials of considerableelectrical conductivity—especially by most metals, byseawaterand by wet ground. Some of these make the use ofradar altimeterspossible. The radar signals that are reflected back towards the transmitter are the desirable ones that make radar work. If the object ismovingeither toward or away from the transmitter, there is a slight equivalent change in thefrequencyof the radio waves, caused by theDoppler effect.
Radar receivers are usually, but not always, in the same location as the transmitter. Although the reflected radar signals captured by the receiving antenna are usually very weak, they can be strengthened byelectronic amplifiers. More sophisticated methods ofsignal processingare also used in order to recover useful radar signals.
The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively long ranges—ranges at which other electromagnetic wavelengths, such asvisible light,infrared light, andultraviolet light, are too strongly attenuated. Such weather phenomena as fog, clouds, rain, falling snow, and sleet that block visible light are usually transparent to radio waves. Certain radio frequencies that are absorbed or scattered by water vapor, raindrops, or atmospheric gases (especially oxygen) are avoided in designing radars, except when their detection is intended.