Extremely high frequency

The short wavelength allows modest size antennas to have a small beam width, further increasing frequency reuse potential.

Millimeter waves are used for military fire-control radar, airport security scanners, short range wireless networks, and scientific research.

[8] At typical power densities they are blocked by building walls and suffer significant attenuation passing through foliage.

Millimeter wavelengths are the same order of size as raindrops, so precipitation causes additional attenuation due to scattering (rain fade) as well as absorption.

[8] Millimeter waves show "optical" propagation characteristics and can be reflected and focused by small metal surfaces and dielectric lenses around 5 to 30 cm (2 inches to 1 foot) diameter.

Ground-based radio astronomy is limited to high altitude sites such as Kitt Peak and Atacama Large Millimeter Array (ALMA) due to atmospheric absorption issues.

These higher frequencies do not suffer from oxygen absorption, but require a transmitting license in the US from the Federal Communications Commission (FCC).

[13] The band is essentially undeveloped and available for use in a broad range of new products and services, including high-speed, point-to-point wireless local area networks and broadband Internet access.

Highly directional, "pencil-beam" signal characteristics permit different systems to operate close to one another without causing interference.

The high usable channel capacity in this band might allow it to serve some applications that would otherwise use fiber-optic communication or very short links such as for the interconnect of circuit boards.

[citation needed] With Raytheon the U.S. Air Force has developed a nonlethal antipersonnel weapon system called Active Denial System (ADS) which emits a beam of millimeter radio waves with a wavelength of 3 mm (frequency of 95 GHz).

[17] The weapon causes a person in the beam to feel an intense burning pain, as if their skin is going to catch fire.

[20] Privacy advocates are concerned about the use of this technology because, in some cases, it allows screeners to see airport passengers as if without clothing.

There is no anatomical differentiation between male and female on the image, and if an object is detected, the software only presents a yellow box in the area.

[24] Recent studies at the University of Leuven have proven that millimeter waves can also be used as a non-nuclear thickness gauge in various industries.

Low intensity (usually 10 mW/cm2 or less) electromagnetic radiation of extremely high frequency may be used in human medicine for the treatment of diseases.