extremely high frequency - traducción al griego
![A CableFree MMW link installed in the UAE installed for [[Safe City]] applications, providing 1Gbit/s capacity between sites. The links are fast to deploy and have a lower cost than fibre optics.](https://commons.wikimedia.org/wiki/Special:FilePath/CableFree MMW Link installed in UAE.jpg?width=200 "A CableFree MMW link installed in the UAE installed for [[Safe City]] applications, providing 1Gbit/s capacity between sites. The links are fast to deploy and have a lower cost than fibre optics.")
![Atmospheric attenuation in dB/km as a function of frequency over the EHF band. Peaks in absorption at specific frequencies are a problem, due to atmosphere constituents such as [[water]] vapour (H<sub>2</sub>O) and molecular [[oxygen]] (O<sub>2</sub>). The vertical scale is logarithmic.](https://commons.wikimedia.org/wiki/Special:FilePath/Micrwavattrp.png?width=200 "Atmospheric attenuation in dB/km as a function of frequency over the EHF band. Peaks in absorption at specific frequencies are a problem, due to atmosphere constituents such as [[water]] vapour (H<sub>2</sub>O) and molecular [[oxygen]] (O<sub>2</sub>). The vertical scale is logarithmic.")
![Soviet aircraft carrier ''Minsk'']]](https://commons.wikimedia.org/wiki/Special:FilePath/Minsk port bow AK-630 CIWS gun fire control radar.JPG?width=200 "Soviet aircraft carrier ''Minsk'']]")
![Part of the [[Atacama Large Millimeter Array]] (ALMA), a millimeter wave [[radio telescope]]](https://commons.wikimedia.org/wiki/Special:FilePath/The Atacama Compact Array.jpg?width=200 "Part of the [[Atacama Large Millimeter Array]] (ALMA), a millimeter wave [[radio telescope]]")
![Typical spectrum of ELF electromagnetic waves in the Earth's atmosphere, showing peaks caused by the [[Schumann resonances]]. The Schumann resonances are the resonant frequencies of the spherical Earth-ionosphere cavity. Lightning strikes cause the cavity to "ring" like a bell, causing peaks in the noise spectrum. The sharp power peak at 50 Hz is caused by radiation from global [[electric power grid]]s. The rise of the noise at low frequencies ''(left side)'' is radio noise caused by slow processes in the Earth's [[magnetosphere]].](https://commons.wikimedia.org/wiki/Special:FilePath/Schumann resonance spectrum.gif?width=200 "Typical spectrum of ELF electromagnetic waves in the Earth's atmosphere, showing peaks caused by the [[Schumann resonances]]. The Schumann resonances are the resonant frequencies of the spherical Earth-ionosphere cavity. Lightning strikes cause the cavity to \"ring\" like a bell, causing peaks in the noise spectrum. The sharp power peak at 50 Hz is caused by radiation from global [[electric power grid]]s. The rise of the noise at low frequencies ''(left side)'' is radio noise caused by slow processes in the Earth's [[magnetosphere]].")
Wikipedia
Extremely high frequency (EHF) is the International Telecommunication Union (ITU) designation for the band of radio frequencies in the electromagnetic spectrum from 30 to 300 gigahertz (GHz). It lies between the super high frequency band and the far infrared band, the lower part of which is the terahertz band. Radio waves in this band have wavelengths from ten to one millimetre, so it is also called the millimetre band and radiation in this band is called millimetre waves, sometimes abbreviated MMW or mmWave. Millimetre-length electromagnetic waves were first investigated by Indian physicist Jagadish Chandra Bose, who generated waves of frequency up to 60 GHz during experiments in 1894–1896.
Compared to lower bands, radio waves in this band have high atmospheric attenuation: they are absorbed by the gases in the atmosphere. Absorption increases with frequency until at the top end of the band the waves are attenuated to zero within a few meters. Absorption by humidity in the atmosphere is significant except in desert environments, and attenuation by rain (rain fade) is a serious problem even over short distances. However the short propagation range allows smaller frequency reuse distances than lower frequencies. 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.
In a major new application of millimeter waves, certain frequency ranges near the bottom of the band are being used in the newest generation of cell phone networks, 5G networks. The design of millimeter-wave circuit and subsystems (such as antennas, power amplifiers, mixers and oscillators) also presents severe challenges to engineers due to semiconductor and process limitations, model limitations and poor Q factors of passive devices.
