HF (3 to 30 MHz)
The very first British radar system chain home used the HF band, but it was soon realised that these frequencies were becoming too crowded with other users and they suffered from too much external noise for serious use.
VHF (300 to 1,000 MHz)
Used for Military airborne early warning (AEW) radars. UHF is good for aircraft and missile detection in the midst of clutter. The large high-powered antennas are also widely available for these applications.
L band (1,000 to 2,000 MHz)
Preferred for long-range air surveillance radar work (200 nautical miles), such as in air traffic control systems that have to track aircraft between airports. The military also has a fondness for L band in space surveillance and missile detection because this band is not very susceptible to nuclear blackout effects as lower frequencies.
S band (2 to 4 GHz)
S band is a very middle of the road band, because lower frequencies are good for long range work and greater frequencies are best suited for getting accurate target information. Used for medium-range airport surveillance work (50 to 60 nautical miles) and long range weather radars. Military 3D radars that determine elevation angle, azimuth angle and range of targets use the S band (sometimes maybe L band).
C band (4 to 8 GHz)
X band (12 to 40 GHz)
K band (12 to 40 GHz)
Usually only used for short-range work because large and powerful enough antennas are hand to come by for this frequency. The K band has been used for airborne radar and short-range airport surface detection (ASDE).
Millimetre waves (40 to 300 GHz)
Millimetre wavelengths have been relatively underused in radar application because of their high sensitivity to the atmosphere. Since outer-space has no atmosphere, millimetre wave radar has been considered for space missions.
Laser radars that operate at infrared and optical frequencies also suffer from high sensitivity to the atmosphere and the waves tend to react in all manner of odd ways especially in bad weather. Although they have been tested for distance measuring in surveying and for precision range finding in weapon control, their main advantage would be probing the nature of our Earth s atmosphere from a spacecraft (maybe even other planets).