Take the light from a flashlight, this is very much like the unseeable light production from a radar. That’s because microwaves act much like light waves. They move in straight lines and they are easily reflected. Objects like vehicles, signs and bridges are the most effective due to their elevated metallic content.

Unlike light, however, you can’t see the radar beam because microwaves are invisible. But they are very easily received by a radio tuned to microwave frequency. In fact, this is the idea that today’s traffic radars are based upon.

Traffic radar performance is a simple issue of pointing the antenna down the road.

When an approaching target comes into range, the radar beam reflects off the target and gets received by the radar.

How Traffic Radar Measures The Speed of Traffic

The radar reflections seen by the radar determine the speed of the target. The Doppler theory is then used to calculate the true speed of the vehicle. You may be familiar with how the Doppler effect works on sound frequencies. With sound waves, you can experience the Doppler effect at railroad tracks. A constant pitch is heard as a train approaches. You will observe a lower pitch at the second the train passes. The train itself is making the same sound both approaching and going, but a stationary listener, the velocity of the train adds to the pitch of its sound as it approaches, and subtracts as it departs. For the train illustration, the difference in pitch between the real train pitch and the pitch a stationary listener experiences is called Doppler Shift and the train’s speed determines degree of the change.

Traffic radar applies this Doppler theory to microwaves.

Specifically, the Doppler principle compares the originally transmitted frequency to the phase-shifted reflected frequency and calculates speed from this difference assuming the radar is functioning properly. However, in some instances the rader may give incorrect results causing you to seek the services of a radar repair facility.

Referring back to the flashlight/spotlight comparison, the radiated light only shines so far giving us limited sight. The more powerful it is, the further it reaches. Microwave beams are no different.

Traffic radar has relatively limited reach due to its low power consumption. As already mentioned, the farther the beams travel to get to the object the weaker they will be at impact. As an example, say an policeman triggers his radar at a target one mile away. But the reflected signal has to travel that identical mile back to the radar before it’s of any value. If the returned microwaves are too small, the radar’s receiver cannot pick-up the reflected signal to calculate speed. If this is the situation, the vehicle is out of reach.

Radar reach depends upon two things: strength of the radar and reflectivity of the object.

The measure of power is determined by the radar’s designer: to the motorist, it’s not a variable. If you think the range is not sufficient anymore you should have it checked-out by a reputable radar repair shop. But reflectivity varies with each target.

On the freeway, beam reflectivity is largely based on size and shape of the target. The smaller the vehicle, the smaller its reflection, and therefore the shorter the range. Therefore, a radar that cannot detect a small car at close range can detect a large car at a longer range.

It is a common practice to send the unit to a radar repair facility so they can perform a series of tests to guarantee accurate readings.