How does police radar work?
A police radar gun operates by transmitting radio waves at certain frequencies which reflects off objects (your vehicle) and are then picked up by the radar gun’s receiving section. When radar waves reflect off a moving target, a measurable frequency shift occurs. The radar unit converts this shift into miles per hour to determine the target’s speed. Two basic types of radar are used – stationary and moving. Stationary radar must be used from a static site, typically a patrol car parked along side the road (See above figure). But with a single antenna moving radar, an officer can clock approaching vehicles while driving on patrol. Moving radar with two antennae – one facing forward, the other aimed out the back of the cruiser – can also clock vehicles even after they have passed by, headed in the opposite direction.
It transmits a radio signal in the microwave band. Upon striking an object some of that signal is reflected back toward the radar and, if that object is moving, a Doppler shift occurs in the radio frequency. The radar then calculates that change in frequency and converts it into either miles per hour or kilometers per hour. Q: What is Doppler shift? A: It’s a scientific principle that an audio, radio or light wave will increase or decrease in frequency upon movement of the source. In the case of police radar the transmitted signals frequency will increase if the target is moving toward the radar transmitter and decrease if it is moving away. It is this difference in frequency that is predictable and is used to calculate the relative speed of the target. An audio Doppler shift can easily be detected when a moving object such as car or aircraft passes near you, the sound seems to decrease in pitch as it passes by. This is because the source is moving relative to your position. The Dopple
