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).

 

General radio band designations
abbreviation	meaning	wavelength	frequency
ELF	extremely low frequency	10,000-100 km	30 Hz-3 kHz
VLF	very low frequency	100-10 km	3-30 kHz
LF	low frequency	10-1 km	30-300 kHz
MF	medium frequency	1 km-100 m	300 kHz-3 MHz
HF	high frequency	100-10 m	3-30 MHz
VHF	very high frequency	10-1 m	30-300 MHz
UHF	ultra high frequency	1 m-10 cm	300 MHz-3 GHz
SHF	super high frequency	10-1 cm	3-30 GHz
EHF	extremely high frequency	1 cm-1 mm	30-300 GHz

 

Only a small part of this spectrum, from about one gigahertz (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.

 

Some IEEE radio band designations
band	frequency	wavelength
L	1-2 GHz	30-15 cm
S	2-4 GHz	15-7.5 cm
C	4-8 GHz	7.5-3.75 cm
X	8-12 GHz	3.75-2.5 cm
Ku	12-18 GHz	2.5-1.67 cm
K	18-27 GHz	1.67-1.11 cm
Ka	27-40 GHz	1.11-0.75 cm