- Radar is an electromagnetic system for the detection and location of objects
(RAdio Detection And Ranging)
- radar operates by transmitting a particular type of waveform and detecting the nature of the signals
reﬂected back from objects
- radar can not resolve detail or colour as well as the human eye (an optical frequency passive scatterometer)
- radar can see in conditions which do not permit the eye to see such as darkness, haze, rain, smoke
- radar can also measure the distances to objects
- the elemental radar system consists of a transmitter unit, an antenna for emitting electromagnetic radiation
and receiving the echo, an energy detecting receiver and a processor.
- a portion of the transmitted signal is intercepted by a reﬂecting object (target) and is reradiated in all directions
- the antenna collects the returned energy in the backscatter direction and delivers it to the receiver
- the distance to the receiver is determined by measuring the time taken for the electromagnetic signal to
travel to the target and back.
- the direction of the target is determined by the angle of arrival (AOA) of the reﬂected signal.
- also if there is relative motion between the radar and the target, there is a shift in frequency of the reﬂected
signal (Doppler effect) which is a measure of the radial component of the relative velocity. This can be used
to distinguish between moving targets and stationary ones.
-Radar was ﬁrst developed to warn of the approach of hostile aircraft and for directing anti aircraft weapons.
- modern radars can provide AOA, Doppler, MTI etc.
- the simplest radar waveform is a train of narrow (0.1µs to 10µs) rectangular pulses modulating a sinusoidal
- the distance to the target is determined from the time TR taken by the pulse to travel to the target and return
and from the knowledge that electromagnetic energy travels at the speed of light thus:
R = ---------R2