The IEEE K band is a portion of the radio spectrum in the microwave range of frequencies ranging between 18 and 27 GHz. K band between 18 and 26.5 GHz is absorbed easily by water vapor (H2O resonance peak at 22.24 GHz, 1.35 cm).
The microwave spectrum is usually defined as electromagnetic energy ranging from approximately 1 GHz to 100 GHz in frequency, but older usage includes lower frequencies. Most common applications are within the 1 to 40 GHz range. Microwave frequency bands, as defined by the Radio Society of Great Britain (RSGB), are shown in the table below:
Footnote: P band is sometimes incorrectly used for Ku Band. "P" for "previous" was a radar band used in the UK ranging from 250 to 500 MHz and now obsolete per IEEE Std 521, see  and . For other definitions see Letter Designations of Microwave Bands