ITU frequency bands

The International Telecommunications Union has defined a system of terminology for electromagnetic frequencies used for radio and radar. While it is probably the most user-friendly of the three major systems in use, its categories are too coarsely grained for describing radar uses. It is, however, a good set of terms for frequencies used in communications.

See IEEE frequency bands for radar designations used widely in civilian practice, and the EU-NATO-US frequency bands for a nomenclature that works well in fine-grained radar band discussion.

The very lowest bands have no radar applications, but, among other things, have a critical military application in communicating, at a very low data rate, with submerged submarines.

Millimeter wave frequencies begin at 18 GHz in SHF and go to the lower third of EHF. Submillimeter wave start roughly above 100 GHz; they blur into the longer infrared light frequencies.