The electromagnetic spectrum is the range of electromagnetic radiation, as measured by their frequencies and wavelengths. The full spectrum extends from a frequency of zero Hertz (infinite wavelength) to infinite Hertz (zero wavelength), though some scientific theories place upper and lower boundaries on the wavelengths as (a) the size of the universe for the upper limit and (b) the Planck length(1) for the lower. Only a limited portion of the full spectrum is of interest to us; mostly those frequencies in the radio/microwave bands.
The International Telecommunications Union (ITU) has subdivided the radio/microwave region of the spectrum into nine frequency bands, as shown below. The designations include a Band Number and a two- or three-letter Abbreviation. By convention, spectrum charts that include frequencies above and/or below the radio/microwave region follow the frequency division pattern and usually provide abbreviations. No band numbers are included, as they are ITU-specific.
Below are three tables listing the spectrum bands in order of increasing frequency. The tables include those bands a) below the radio/microwave bands; b) the radio/microwave bands; and c) those above the radio/microwave bands.