How Radar Guns Work
History of Radars
Radar is an electronic tool which uses electromagnetic waves called radio waves to detect and locate moving or fixed objects. The word "Radar" is an abbreviation for Radio Detection and Ranging.
Today, small and efficient radar units, such as Decatur Speed Trak Police Radar, can be found in almost every police vehicle. It is estimated that 20 million speeding citations are issued annually and that police radars are used in 13 million of these cases. It is imperative that police officers using police radar guns are well-trained and have a good working knowledge of how radar works, because oversimplification of principles behind radar operations can lead to a variety of misunderstandings and errors.
There are Two Types of Radars:
Police Radar utilizes radio waves and the Doppler Effect. Police Laser Radar (Lidar) utilizes light waves and the pulse principle.
- Pulse Radar
- Continuous Wave Radar
Doppler Principle states that the measured frequency of a wave is relative to the motion between the source and the observer. The Doppler Principle can be applied to sound waves, light waves, and radio waves. Doppler Principle is a basis for all modern police radar. In short, Doppler Principle states that when a radar signal hits the object that is moving toward the observer/patrol vehicle, the returning frequency will be higher than the original. When the signal hits that object/vehicle that is moving away from the observer, the returning frequency will be lower than the original one. The frequency change can be used to determine the speed of the target vehicle. Click here for more information on Doppler Principle and Doppler Shift.
How Does Radar Work
A Radar Gun is used to send out radio waves of specific frequencies in a chosen direction. The traveling waves then bounce off objects, including vehicles, and return to the radar gun 's receiving station. When the waves reflect off a moving vehicle, a measurable frequency shift, called Doppler Shift, occurs. The radar gun computer then uses the frequency shift to calculate the speed of the moving vehicle.
A good analogy for a radar signal is a beam of light from a flashlight. When one shines a flashlight at an object, the object can be seen thanks to the light reflected from the object. Now imagine yourself as the object that at which the light is aimed. The target (the object at which the light is being pointed) can see the light from the flashlight from a much farther distance than the person with the flashlight could ever hope to see the target. That's because the beam loses energy over distance. So while the beam has enough energy to reach the target, the reflected light doesn't have enough energy to travel all the way back to where it started.
Police Radar Guns "see" a vehicle by transmitting a microwave pulse that reaches the target and then comes back to the observer. Then, the Doppler Effect is applied: the frequency of the transmitted pulse is compared to the frequency of the reflection, and speed is calculated by using the difference between the two frequencies.
The idea behind Radar Detectors is the following. The Radar Detector looks for radar "beams" and finds them before they can return a strong enough reflection to "illuminate" you. Radars are essentially microwave radio receivers that make noise or flash lights when they sense an incoming signal on specific frequencies. Superheterodyne reception allows detection of radar around curves or over hills, and it extends detection range straight ahead.
It is essential that police officers and other personnel who use radar guns have a clear understanding of basic Radar Principles. Oversimplifying the latter information can lead to a variety of misunderstandings and errors.
One common area of misunderstanding is in regard to the radar beam .
The Radar Beam
The radar antenna transmits the signal in a directional beam similar to the configuration of a flashlight beam. A police traffic radar beam is conical in shape and continues outward indefinitely from the antenna until it is reflected, refracted, or absorbed.
Main Power Beam - Between 80% and 85% of the transmitted radar energy is contained in a 12 degree central beam known as the main power beam. The remaining power is contained outside the main power beam. Please click here for more information about the Radar Beam.
Understanding of several other important Radar Facts /
Rules is essential for grasping the principle behind radar gun functions:
- Inverse Square
- Contour Lines of Equal
Sensitivity and Beam Range Sensitivity
- Cosine Effect
Reflectivity Effects - Target Size, Shape and Composition Effects
Police radar transmits low level, non-ionizing radio frequency electromagnetic radiation.
According to scientific research in this area, the emission levels resulting from traffic radar do not pose risk to the operator of the radar or the occupants of vehicles being targeted.
Range Control Techniques
While understanding basic principles of radar gun work, it is also important to learn how a radar operator can control the effective range of the radar and how to adjust the radar beam to avoid possible errors in target identification. There are three methods to control range.
1. Sensitivity (Range) Control Functions - can be turned down to decrease the sensitivity of the radar gun. A reduction in sensitivity does not change the transmitting power and the reduction in sensitivity is the same across all of the reflected signals.
2. Tilting or Angling the Antenna - permits the operator to change or move the main power beam and the zone of influence. Tilting or angling the radar antenna should only be done in the stationary mode. The tilting does not change the relative speed between the target vehicle and the radar unit; therefore, there is no cosine effect in the stationary mode. Tilting the antenna in the moving mode will create a cosine effect in the low Doppler.
3. Environmental interference, such as hills and curves, will reduce the effective range of the radar gun. The radar beam continues in a straight path and cannot bend around curves or over hills. Police traffic radar is basically a line-of-sight speed measuring device.
The Doppler Audio
The Doppler Audio is a useful tool to help the operator during the initial observation and identification of the target vehicle. It can help avoid selectivity problems and to eliminate possible sources of interference. Please click here for more information on Doppler Audio .
Lidar - Basic Information, Lidar
For more information on Lidar, please click here.
- Lidar (Laser Radar) means - Light Detection And Ranging.
- How Does a Lidar Works?- Lidar is measure by the time and distance (Flight of Speed) to get you a speed-reading of the target.
- Laser Radar utilizes two methods to determine speed: Pulse Principle and Speed of Light Constant.