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What is X, K, Ka, and Ku Radar?

Radar is short for RAdio Detection And Ranging and is the use of radio waves to determine the range, location, and speed of an object. Police use radar by focusing radio waves at an area (or object such as a car) and then measuring the radio wave that is reflected back. By using the Doppler effect they can then determine an objects speed.

Police use a radar "gun" that was invented by Bryce K. Brown in March 1954. Most radar guns used by law enforcement today are a basic variation on the original design.

A radar gun is a simple radio transmitter and receiver. The radio waves sent have a frequency measured in Gigahertz (GHz). When the radio waves reflect and bounce off of an object there is a slight change in frequency. The frequency shift (Doppler effect) is measured by the radar gun and the objects speed is determined.

The frequencies used by the radar guns are called radar bands. X band was once the most common but is becoming rather rare since it is very easily detected by radar detectors. K and Ka bands use frequencies that are much more difficult to detect and are now more common. Ku band is mostly found in Europe.


  • X Band is in the 8.0 to 12.0 GHz range (most common is 10.5 in the US / 9.4-10.6 in Europe)

  • K Band is in the 18 to 26.5 GHz range (most common is 24.12 - 24.17 in the US / 24.12 - 25.15 in Europe)

  • Ka Band is in the 26.5 to 40 GHz range (most common is 33.8, 34.6, 34.7, 35.5, 35.7 GHz in the US / 34.0, 34.3, 35.5 in Europe)

  • Ku Band is in the 12 to 18 GHz range (Ku is not used in the US, most common is 13.45 in Europe)


A radar detector is a radio receiver designed to scan for these frequencies. When it detects radio waves in the X, K, Ka, or Ku band it sends out an alert, and many detectors will even tell you how strong (close) the signal is. High performance detectors usually are able to alert faster, detect radar at a greater distance, and also filter out false radio signals better than entry level designs, but they all perform essentially the same function.

In the US most radar guns used by police are K or Ka band, however some police departments still use X band. We know that a lot of people advocate turning X band off, but before you do we recommend driving around for a while with it on to make certain you do not encounter any police still using the band in your area. In fact, some departments now purposefully use X band because so many people treat it as a false alert and turn it off.

In addition to being used by police, many automatic doors and some car navigation systems emit radar as well. This results in false alerts. The signal from an automatic door, etc... is often rather weak so most radar detectors have a city mode to lessen the detectors sensitivity. A few radar detector models also allow you to manually lock out false signals, or will even block them for you automatically.

How you setup your radar detector can also be a determining factor in how effective it is. First, the detector should be placed so that the forward sensor has an unobstructed "view" ahead. For a windshield mount detector, the best location is in the center, and middle of the windshield. The detector should also be level and not pointing up, or down. You may want to turn off X band depending on where you live. Next, in town set the detector to city mode to lessen the number of false alerts, and switch back to highway when outside of urban areas. There are compromises in setting up your detector related to how tolerant you are of false alerts. Some prefer to use highway mode constantly, others will never turn off X band. As you use your detector you will be able to decide what you want to change from the basic settings.

Certain radar detector models are better for highway use where you want long range, and very quick detection, but they tend to have a lot of false alerts in urban area. There are other models that tend to be much better at filtering out false alerts but may not alert fast enough for someone that travels mostly on the interstate. Because of this, here at Buy Radar Detectors we work with you to find the radar detector that fits your specific needs.

3 Comments

Can I use the STI-R detector in Belgium ( Europe)?
Do you deliver in Belgium?
I want to buy a STI-r model .

The Beltronics STi-R Concealed Radar Detector has been discontinued and is no longer available. It was replaced by the Escort 9500ci Concealed Radar Detector / Laser Shifter.

My Whistler 1730 is VG2 undetectable. Is VG2 still a factor for me to be concerned about or is it obsolete?

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