What Is K-band?

K-band is a segment of the microwave radio spectrum spanning 18 to 27 gigahertz (GHz), corresponding to free-space wavelengths of approximately 1.7 to 1.1 centimeters. The designation was formalized in IEEE Standard 521-2019 on letter designations for radar-frequency bands, which standardizes the letter-band notation in widespread use among radar and microwave engineers since World War II. The letter K derives from the German word Kurz, meaning short, reflecting the relatively short wavelength of radiation in this portion of the microwave spectrum. K-band sits between the Ku-band (12 to 18 GHz) and the Ka-band (27 to 40 GHz), and the three together are sometimes referred to collectively as the K-bands.

A defining characteristic of K-band is that it includes the resonant absorption frequency of water vapor at 22.24 GHz. Atmospheric water vapor absorbs strongly at this frequency, introducing path loss that increases with humidity and propagation distance. This absorption makes the center of the K-band poorly suited for long-distance communication links but has no practical effect on short-range systems operating below roughly one kilometer.

Radar Applications

K-band is widely used in short-range radar systems where compact antenna size and high range resolution are priorities. The short wavelength allows small antennas to achieve narrow beamwidths, supporting precise angular resolution in vehicle-detection and motion-sensing systems. Police speed enforcement radars operating at 24.125 and 24.150 GHz are among the most familiar K-band applications. K-band frequency-modulated continuous-wave (FMCW) radar is used in automotive applications including blind-spot monitoring, rear cross-traffic alert, and short-range collision warning, complementing the longer-range 77 GHz systems. The IEEE conference paper on a K-band FMCW radar for vehicle speed detection illustrates the signal processing techniques used in these systems. Ground-based precipitation radars operated by national weather services also use K-band frequencies, where water vapor absorption is exploited rather than avoided to measure humidity profiles in the lower atmosphere.

Satellite and Fixed Wireless Links

K-band frequencies are used in fixed satellite service (FSS) uplinks and in fixed terrestrial point-to-point links where the service distances are short enough to keep water vapor attenuation within acceptable bounds. Local multipoint distribution service (LMDS) systems operating in the lower K-band allocated frequencies have been used for last-mile broadband delivery. K-band monolithic microwave integrated circuit (MMIC) technology, fabricated in GaAs or GaN processes, enables compact solid-state power amplifiers and low-noise amplifiers for both satellite ground terminals and point-to-point radio equipment. MMIC integration reduces system cost and size compared to waveguide-based approaches and has extended K-band equipment into automotive, consumer, and industrial markets. Technical parameters for K-band satellite allocations are defined in ITU Radio Regulations Appendix 4, which specifies frequency assignments and coordination requirements for geostationary and non-geostationary services.

Band Relationships and Propagation Tradeoffs

K-band occupies a transitional position in the microwave spectrum, inheriting some propagation characteristics of the adjacent Ku and Ka bands. It experiences less rain fade than Ka-band but more than Ku-band, and its atmospheric absorption peak at 22.24 GHz has historically led system designers to split allocations between the Ka and Ku bands for long-haul links. For systems where absolute link distance is secondary, such as automotive radar, security imaging, or industrial level sensing, the propagation constraints are not limiting and K-band's compact antenna geometry and mature MMIC supply chain are advantages.

Applications

K-band has applications in a wide range of fields, including:

• Automotive radar for blind-spot detection and collision avoidance
• Law enforcement vehicle speed measurement
• Fixed wireless and last-mile broadband links
• Weather radar and atmospheric humidity profiling
• Industrial proximity sensing and level measurement
• Satellite communications ground terminals