Radar is an object detection system that uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain.

(a) Primary Radar: Uses the principle of pulse technique to determine the range and bearing of an object. Working on the echo and searchlight principle, a transmitter transmits pulses. All objects in the path of the pulses will reflect and scatter this energy. Some of the reflected energy reaches the receiver. The reflected energy is processed to give the required information. In this radar, the object‟s cooperation is not required in the entire process.

(b) Secondary Radar: A transmitter transmits a group of pulses. An aerial in the path of the pulses receives the signals and passes it to the receiver. If the pulses are identified, then the transmitter gives out a reply. In this radar active cooperation of the other object is also required.

(c) Continuous Wave Radar: In this type of radar, both the transmission and the reception take place continuously. This requires a set of two aerials, one for transmission and one for the reception.