Radar gun

speed gunradar speed gunradarRadar trapsfixed radarslaw enforcement radarpolice radar equipmentpolice speed radarRadar Gunsradar speed detection
A radar speed gun (also radar gun and speed gun) is a device used to measure the speed of moving objects.wikipedia
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Doppler radar

DopplerDoppler navigationDoppler navigation radar
A radar speed gun is a Doppler radar unit that may be hand-held, vehicle-mounted or static.
Doppler radars are used in aviation, sounding satellites, Major League Baseball's StatCast system, meteorology, radar guns, radiology and healthcare (fall detection and risk assessment, nursing or clinic purpose ), and bistatic radar (surface-to-air missiles).

LIDAR traffic enforcement

LIDARLaser speed guntraffic speed guns
Such devices are frequently used for speed limit enforcement, although more modern LIDAR speed gun instruments, which use pulsed laser light instead of radar, began to replace radar guns during the first decade of the twenty-first century, because of limitations associated with small radar systems.
Lidar has a wide range of applications; one use is in traffic enforcement and in particular speed limit enforcement, gradually replacing radar after 2000.

Radar detector

radar detectorscar radar detectorsspeed detection radar
Some motorists install radar detectors which can alert them to the presence of a speed trap ahead, and the microwave signals from radar may also change the quality of reception of AM and FM radio signals when tuned to a weak station.
A radar detector is an electronic device used by motorists to detect if their speed is being monitored by police or law enforcement using a radar gun.

Speed limit enforcement

speed trapspeed trapsspeeding
Such devices are frequently used for speed limit enforcement, although more modern LIDAR speed gun instruments, which use pulsed laser light instead of radar, began to replace radar guns during the first decade of the twenty-first century, because of limitations associated with small radar systems. Some motorists install radar detectors which can alert them to the presence of a speed trap ahead, and the microwave signals from radar may also change the quality of reception of AM and FM radio signals when tuned to a weak station. Cameras are associated with automated ticketing machines (known in the UK as speed cameras) where the radar is used to trigger a camera.
More recently, radar guns and automated in-vehicle systems have come into use.

X band

XX-bandX-
Modern radar speed guns normally operate at X, K, K a, and (in Europe) K u bands.
X band radar frequency sub-bands are used in civil, military, and government institutions for weather monitoring, air traffic control, maritime vessel traffic control, defense tracking, and vehicle speed detection for law enforcement.

Ku band

K u bandK u -bandK u
Modern radar speed guns normally operate at X, K, K a, and (in Europe) K u bands.
Some frequencies in this radio band are employed in radar guns used by law enforcement to detect vehicles speeding, especially in Europe.

Continuous-wave radar

continuous wave radarcontinuous wave illuminating radarscontinuous-wave
A second limitation for hand-held devices is that they have to use continuous-wave radar to make them light enough to be mobile.
This is a typical problem with radar speed guns used by law enforcement officers, NASCAR events, and sports, like baseball, golf, and tennis.

Traffic enforcement camera

speed cameraspeed camerasphoto radar
Cameras are associated with automated ticketing machines (known in the UK as speed cameras) where the radar is used to trigger a camera.
Radar gun

Vehicle

vehiclesvehicularroad vehicle
It is used in law-enforcement to measure the speed of moving vehicles and is often used in professional spectator sport, for things such as the measurement of bowling speeds in cricket, speed of pitched baseballs, athletes and tennis serves.

Baseball (ball)

baseballbaseballsball
It is used in law-enforcement to measure the speed of moving vehicles and is often used in professional spectator sport, for things such as the measurement of bowling speeds in cricket, speed of pitched baseballs, athletes and tennis serves.

Doppler effect

Dopplerdoppler shiftDoppler shifts
It measures the speed of the objects at which it is pointed by detecting a change in frequency of the returned radar signal caused by the Doppler effect, whereby the frequency of the returned signal is increased in proportion to the object's speed of approach if the object is approaching, and lowered if the object is receding. Due to a phenomenon called the Doppler effect, if the object is moving toward or away from the gun, the frequency of the reflected radio waves when they come back is different from the transmitted waves.

Laser

laserslaser beamlaser light
Such devices are frequently used for speed limit enforcement, although more modern LIDAR speed gun instruments, which use pulsed laser light instead of radar, began to replace radar guns during the first decade of the twenty-first century, because of limitations associated with small radar systems.

World War II

Second World WarwarWWII
The radar speed gun was invented by John L. Barker Sr., and Ben Midlock, who developed radar for the military while working for the Automatic Signal Company (later Automatic Signal Division of LFE Corporation) in Norwalk, CT during World War II.

Grumman

Grumman AircraftGrumman Aircraft Engineering CorporationGrumman Aerospace Corporation
Originally, Automatic Signal was approached by Grumman Aircraft Corporation to solve the specific problem of terrestrial landing gear damage on the now-legendary PBY Catalina amphibious aircraft.

Consolidated PBY Catalina

CatalinaPBY CatalinaPBY
Originally, Automatic Signal was approached by Grumman Aircraft Corporation to solve the specific problem of terrestrial landing gear damage on the now-legendary PBY Catalina amphibious aircraft.

Merritt Parkway

MerrittMerritt Parkway Commission
After the war, Barker and Midlock tested radar on the Merritt Parkway.

Connecticut State Police

Connecticut State TrooperState PoliceConnecticut Auxiliary State Police
In 1947, the system was tested by the Connecticut State Police in Glastonbury, Connecticut, initially for traffic surveys and issuing warnings to drivers for excessive speed.

Glastonbury, Connecticut

GlastonburyEast GlastonburyGlastonbury, CT
In 1947, the system was tested by the Connecticut State Police in Glastonbury, Connecticut, initially for traffic surveys and issuing warnings to drivers for excessive speed.

Garden City, New York

Garden CityGarden City, NYGarden City, Long Island
In 1948, radar was also used in Garden City, New York.

Transmitter

radio transmittertransmittersradio transmitters
Radar speed guns, like other types of radar, consist of a radio transmitter and receiver.

Radio receiver

receiverreceiversRadios
Radar speed guns, like other types of radar, consist of a radio transmitter and receiver.

Frequency

frequenciesperiodperiodic
Due to a phenomenon called the Doppler effect, if the object is moving toward or away from the gun, the frequency of the reflected radio waves when they come back is different from the transmitted waves.

Speed of light

clight speedvelocity of light
where c is the speed of light, f is the emitted frequency of the radio waves and Δf is the difference in frequency between the radio waves that are emitted and those received back by the gun.

Frequency mixer

mixerfrequency mixingmixed
After the returning waves are received, a signal with a frequency equal to this difference is created by mixing the received radio signal with a little of the transmitted signal.

Musical note

notenotesmusical notes
Just as two different musical notes played together create a beat note at the difference in frequency between them, so when these two radio signals are mixed they create a "beat" signal (called a heterodyne).