Editing Extremely high frequency (section)

{{short description|The range 30–300 GHz of the electromagnetic spectrum}}
{{MWband
| name = Extremely high frequency
| freq = 30 to 300 [[Hertz|GHz]]
| wave = 10–1 [[Meter|mm]]
| bands = {{startplainlist|class=nowrap}}
* [[K band (NATO)|K]]{{\}}[[L band (NATO)|L]]{{\}}[[M band (NATO)|M]] (NATO)
* [[Ka band|K<sub>a</sub>]]{{\}}[[V band|V]]{{\}}[[W band|W]]{{\}}mm (IEEE)
{{endplainlist}}
| name2 = Millimetre band (IEEE)
| freq2 = 110 to 300 GHz
| wave2 = 2.73 to 1 mm
| bands2 = EHF (IEEE)
}}

'''Extremely high frequency''' (EHF) is the [[International Telecommunication Union]] designation for the band of radio frequencies in the [[electromagnetic spectrum]] from 30 to 300 gigahertz (GHz).<ref name="1037B">{{cite book | title = US Federal Standard 1037B: Telecommunications, Glossary of Telecommunications Terms | publisher = Office of Technology Standards, General Services Administration | date = 3 June 1991 | pages = S-18 | url = https://books.google.com/books?id=zYLXU4fkD34C&pg=RA15-PA18}}</ref><ref name="itu-2015-acts">{{cite conference |date=2015 |title=Final Acts WRC-15 |url=https://www.itu.int/dms_pub/itu-r/opb/act/R-ACT-WRC.12-2015-PDF-E.pdf |conference=World Radiocommunication Conference |location=Geneva, Switzerland |publisher=International Telecommunications Union |pages = 4|access-date=2025-01-12}}</ref> It is in the [[microwave]] part of the radio spectrum, between the [[super high frequency]] band and the [[terahertz band]]. [[Radio wave]]s in this band have [[wavelength]]s from ten to one millimeter, so it is also called the '''millimeter band''' and radiation in this band is called '''millimeter waves''', sometimes abbreviated '''MMW''' or '''mmWave'''.<ref name=Bose>{{cite web |title=Milestones: First Millimeter-wave Communication Experiments by J.C. Bose, 1894-96 |url=https://ethw.org/Milestones:First_Millimeter-wave_Communication_Experiments_by_J.C._Bose,_1894-96 |website=[[List of IEEE milestones]] |date=14 June 2022 |publisher=[[Institute of Electrical and Electronics Engineers]]}}</ref> 

Some define '''mmWaves''' as starting at 24 GHz, thus covering the entire [[5G NR frequency bands#Frequency Range 2|FR2]] band (24.25 to 71 GHz), among others.<ref>{{cite web |url=https://www.wired.com/story/wired-guide-5g/ |title=The WIRED Guide to 5G |date=Dec 31, 2022 |journal=Wired}}</ref><ref>{{cite web |url=https://www.5gradio.com/5g-technology/5g-nr-frequency-bands/ |title=5G NR frequency bands |date=2020 |publisher=CableFree Networks}}</ref>

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 [[Beamwidth|beam width]], further increasing frequency reuse potential. Millimeter waves are used for military [[fire-control radar]], [[millimeter wave scanner|airport security scanners]], short range [[wireless network]]s, and scientific research.

In a major new application of millimeter waves, certain [[5G NR frequency bands#Frequency Range 2|frequency ranges]] near the bottom of the band are being used in the newest generation of [[cell phone]] networks, [[5G]] networks.<ref>{{Cite tech report
| title = User Equipment (UE) radio transmission and reception; Part 3: Range 1 and Range 2 Interworking operation with other radios
| version = 3GPP TS 38.101-3 version 15.2.0 Release 15
| institution = ETSI
| type = Technical Specification
| date = July 2018
| access-date = 5 December 2019
| url = https://www.etsi.org/deliver/etsi_ts/138100_138199/13810103/15.02.00_60/ts_13810103v150200p.pdf
| page = 11
}}</ref> 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 factor|''Q'' factors]] of passive devices.<ref name="duPreez">{{cite book
 | last1  = du Preez
 | first1 = Jaco
 | last2  = Sinha
 | first2 = Saurabh
 | title  = Millimeter-Wave Power Amplifiers
 | publisher = Springer
 | date   = 2017
 | pages  = 1–35
 | url    = https://books.google.com/books?id=Z7M4DwAAQBAJ
 | isbn   = 978-3-319-62166-1
 }}</ref>