K_a band

The K_a band (pronounced as either "kay-ay band" or "ka band") is a portion of the microwave part of the electromagnetic spectrum defined as frequencies in the range 26.5–40 gigahertz (GHz),[1] i.e. wavelengths from slightly over one centimeter down to 7.5 millimeters.[2] The band is called K_a, short for "K-above" because it is the upper part of the original NATO K band, which was split into three bands because of the presence of the atmospheric water vapor resonance peak at 22.24 GHz (1.35 cm), which made the center unusable for long range transmission. The 30/20 GHz band is used in communications satellite uplinks in either the 27.5 GHz and 31 GHz bands,[3] and high-resolution, close-range targeting radars aboard military airplanes. Some frequencies in this radio band are used for vehicle speed detection by law enforcement.[4] The Kepler Mission used this frequency range to downlink the scientific data collected by the space telescope.

The designation "K_a-band" is from Kurz-above, which stems from the German word kurz meaning "short".[5]

In satellite communications, the K_a band allows higher bandwidth communication. It was first used in the experimental ACTS Gigabit Satellite Network, and is currently used in the Inmarsat I-5 system[6] and the SpaceX Starlink system[7] and will be used in the Iridium Next satellite series, Amazon's Project Kuiper satellite internet constellation,[8] Kacific K-1 satellite, as well as the James Webb Space Telescope.

The K_a band is more susceptible to rain attenuation than is the K_u band, which in turn is more susceptible than the C band.[9] The frequency is commonly used by cosmic microwave background experiments. The 5th generation mobile networks will also partially overlap with K_a band (28, 38, and 60 GHz).