Because the complete radio spectrum is so broad it is considered to be divided up into bands, ranging from extremely low frequency (longest wavelengths) to extremely high frequency (shortest wavelengths).
Only a small part of this spectrum, from about one GHz to a few tens of GHz, is used for practical radio communications. International agreements control the usage and allocation of frequencies within this important region. Communications bands are designated by letters that appear to have been chosen at random-S, C, X, and so on. Indeed, this is exactly how they were chosen. The band letters originate from World War II when reference to which frequency bands were being used needed to be kept secret. Most commercial communications use the C (the first to be used), Ku, K, and Ka bands. The shorter wavelength bands, such as Ka are used in conjunction with small (including handheld) receivers on the ground but suffer severe attenuation from rain. The X-band is used heavily for military applications.
Related category RADIO ASTRONOMY AND COMMUNICATIONS
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