Radar speed gun (also radar gun or speed gun) is a small Doppler Radar unit used to detect the speed of moving objects, including vehicles, pitched baseballs, runners and other moving objects. Radar speed guns may be hand-held, vehicle-mounted or static. A radar speed gun measures the speed of objects at which it is pointed by detecting a change in frequency of the returned radar signal due to the Doppler effect). Modern radar speed guns normally operate at X, K, Ka, IR Band (infrared), and (in Europe) Ku bands.

Radar speed guns, like other types of radar, consist of a radio transmitter and receiver. They send out a radio signal, then receive the same signal back as it bounces off the target object. However, due to a phenomenon of Doppler effect, if the object is moving, the frequency of the radio waves is different when they come back, and from that difference the radar speed gun can calculate the object’s speed.

Moving-Object Radar Speed Guns

The above-described system measures the difference in speed between the target and the radar speed gun itself. The gun must be stationary to give a correct reading; if the gun is used from a moving car it just gives the difference in speed between the two vehicles. So a different system is used in radar speed guns designed to work from moving vehicles. In so-called “moving radar”, the gun receives reflected signals from both the target vehicle and stationary background objects, such as the road, road signs, guard rails, streetlight poles, etc. Instead of comparing the frequency of the signal reflected from the target with the transmitted signal, it compares the target signal with the background signal. The difference in frequency of these two signals gives the true speed of the target vehicle.

Applications of Radar Speed Guns

Moving-Object Radar Speed GunRadar speed guns are frequently used for speed limit enforcement although more modern LIDAR speed gun devices which use pulsed laser light instead of radar. Some motorists install radar detectors which can detect signals from radar speed gun devices to avoid being caught. In many countries, it is illegal to use the radar detectors.

Radar speed guns are also used for road-traffic maintenance, police patrolling vehicle chasing, speed measurement of objects in games (football/cricket ball speed measurement), bicycle and motorcycle speed measurement during racing, etc.