![]() Microwaves are widely used in modern technology, for example in point-to-point communication links, wireless networks, microwave radio relay networks, radar, satellite and spacecraft communication, medical diathermy and cancer treatment, remote sensing, radio astronomy, particle accelerators, spectroscopy, industrial heating, collision avoidance systems, garage door openers and keyless entry systems, and for cooking food in microwave ovens. ![]() At the high end of the band, they are absorbed by gases in the atmosphere, limiting practical communication distances to around a kilometer. Microwaves travel by line-of-sight unlike lower frequency radio waves, they do not diffract around hills, follow the earth's surface as ground waves, or reflect from the ionosphere, so terrestrial microwave communication links are limited by the visual horizon to about 40 miles (64 km). The boundaries between far infrared, terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study. Rather, it indicates that microwaves are "small" (having shorter wavelengths), compared to the radio waves used prior to microwave technology. The prefix micro- in microwave is not meant to suggest a wavelength in the micrometer range. Frequencies in the microwave range are often referred to by their IEEE radar band designations: S, C, X, K u, K, or K a band, or by similar NATO or EU designations. In all cases, microwaves include the entire SHF band (3 to 30 GHz, or 10 to 1 cm) at minimum. A more common definition in radio-frequency engineering is the range between 1 and 100 GHz (wavelengths between 0.3 m and 3 mm). ![]() Different sources define different frequency ranges as microwaves the above broad definition includes UHF, SHF and EHF ( millimeter wave) bands. Microwave is a form of electromagnetic radiation with wavelengths ranging from about 30 centimeters to one millimeter corresponding to frequencies between 1 GHz and 300 GHz respectively. The apertures of the dishes are covered by plastic sheets ( radomes) to keep out moisture. A telecommunications tower with a variety of dish antennas for microwave relay links on Frazier Peak, Ventura County, California. For other uses, see Microwaves (disambiguation). For the cooking appliance, see Microwave oven. This article is about the electromagnetic wave.
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