How radar works?

A radar works by an Antennae, or a Dish sending pulses of Radio Waves which then reflect off of any object in their path. The reflection bounces back and then is detected by the dish or antennae. Radar can be used to track speed, distance and even direction.

The Doppler Effect:

The Doppler effect is what happens when an object is moving closer or away from the radio transmitter and the Radio Waves. If an object is moving closer it compresses the radio waves and produces a higher frequency. If it is moving away it stretches the waves creating a lower frequency.

http://www.explainthatstuff.com/radar.html

http://www.physicsclassroom.com/Class/waves/u10l3d3.gif