Radar has snared speeding drivers since the early 1950s. Handheld radar guns have evolved ever since to increase range, improve targeting and outwit radar detectors. Radar's microwaves, which reflect off objects to indicate speed, have climbed in frequency from the original X band (10.525 gigahertz) to K band (24.150 GHz) in the 1970s to Ka band (33.4 to 36.0 GHz) in the late 1980s. The microwave power output is a relatively harmless 15 to 50 milliwatts.

In 1991 manufacturers unveiled laser radar, or lidar. It nails motorists with 904-nanometer infrared light. Lidar's chief advantage is its narrow beam, only three feet wide at 1,000 feet downfield, enabling an officer to pick out a speeding car or motorcycle among three vehicles abreast, says Steve Hocker, product manager at Kustom Signals, a radar and lidar manufacturer in Lenexa, Kan. The microwave cone emitted by a radar gun is about 12 degrees, or 210 feet wide at 1,000 feet. Fog, rain and snow, however, reduce lidar's accuracy; they do not affect radar's accuracy, although they might reduce its range. The average lidar unit costs $3,500, whereas the average handheld radar gun costs $1,300.

Four U.S. manufacturers produce almost all domestic police radar guns. They also make devices to measure the velocity of baseballs and speedboats, to regulate speed in the automatic coupling of railroad boxcars and to determine scientific data such as the flow rate of rising rivers, used to predict flooding. A typical radar unit has a 0.75-mile range and lasts 15 years, according to Jim Hester, general manager of Decatur Electronics's radar manufacturing division in Fort Collins, Colo. The total radar gun market is about $30 million a year.

   
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