How do radar guns work?

• Radar

  • A radar gun is hand-held/or mounted device that is used to detect the speed of a moving object. The term "radar" originated as an acronym for radio detection and ranging. Early radar devices were used primarily to locate objects and to determine the relative distance of an object from the radar device. This was accomplished with the use of radio waves. Radar guns work based on the same principles as the original radar devices, but they are used specifically to detect the speed of objects that have been located.

  Radio Waves

  • 
    Radar guns (and radar in general) work because they have both a radio transmitter and a radio receiver. The radio transmitter in a radar gun sends out radio waves that are directed at a specific object. Once the radio waves hit that object, the waves echo back to the radar gun. Because radio waves always travel at the same speed, the amount of time it takes for the radio waves to return to the radar gun will provide a measurement of the object's distance from the gun.

  Moving Objects

  • When a radar gun is being used to measure the speed of a moving object, the radio waves that are sent out by the radar gun are echoed back to the gun in a different pattern because the object is moving. So while the speed of the radio waves is the same, they return in a different wave pattern. A radar gun is able to detect the change in the wave pattern and the frequency of wave pattern changes to translate this information into a measurement of speed.

Types Of Radar


X-Band:
The first frequency band allocated for police radar: 10.5 - 10.55 GHz. Dating from the 1950s, X-band radar is the easiest to detect because of its lower frequency and higher power output. Depending on terrain, temperature and humidity, X-band radar can be detected from a distance of 2 to 4 miles, yet it can only take accurate readings of speed from a distance of 1/2 mile or less.

K-Band:
The most frequently used radar frequency band: 24.05 - 24.25 GHz. K-band made its appearance in 1978. The first K-band hand-held radar guns could only be used from a stationary position. Later, a "pulsed" version was introduced that could be used from a stationary or moving vehicle.

K-band radar waves have a relatively small wavelength. At the power level found in police radar guns, K-band has an effective clocking range of about 1/4 mile. Depending upon terrain (around a corner, over a hill, etc.), K-band waves can be detected from a range of 1/4 mile to 2 miles.

Ka-Band:
In 1987 the FCC allocated a frequency on yet another band, Ka, for police radar use. Ka-Band incorporates Ka-band, Ka Wide-Band, and Ka Super Wide-Band. With Ka came the introduction of photo radar (also known as "photo-cop"). The photo-cop system works at 34.3 GHz and combines a Ka-band radar gun with an automated camera (see Photo Radar below).

The FCC later expanded Ka-band radar use to a range of 34.2 to 35.2 GHz. This became known as Ka Wide-Band.

The introduction of the "stalker" radar gun raised the stakes in the detection game. Unlike all previous guns, the Stalker can be FCC licensed for any frequency in the Ka-band between 33.4 GHz to 36.0 GHz, and so cannot be picked up by detectors designed only for X, K, and photo radar. Stalker guns are being used in more than half the country.

In response, manufacturers have developed detectors with "Super wide-band" technology that sweeps all of the Ka-band allocated to radar, as well as providing continued protection against X, K, and photo radar.

Ku-Band:
Ku-band radar ranges between 12 and 18 GHz. It is used primarily for satellite communications, in both aerospace and broadcasting. It is used primarily in Europe and not seen much in America. In the radar enforcement realm, Ku is set at 13.45 GHz by the FCC and has only recently been introduced to the U.S. for speed detection.