Editing Microwave (section)

== Electromagnetic spectrum ==
Microwaves occupy a place in the [[electromagnetic spectrum]] with frequency above ordinary [[radio wave]]s, and below [[infrared]] light:
{| class="wikitable nowrap" style="text-align:center;"
!colspan="5"| [[Electromagnetic spectrum]]
|-
! Name || Wavelength || [[Hertz#SI multiples|Frequency (Hz)]] || [[Photon]] [[energy]] ([[Electronvolt#Properties|eV]])
|-
| [[Gamma ray]]     || < 0.01&nbsp;nm        || > 30 [[Exa-|E]]Hz || > 124 [[kilo-|k]]eV     
|-
| [[X-ray]]         || 0.01&nbsp;nm – 10&nbsp;nm  ||  30 EHz – 30 [[Peta-|P]]Hz || 124 keV – 124 eV
|-
| [[Ultraviolet]]   ||   10&nbsp;nm – 400&nbsp;nm ||  30 PHz – 750 THz ||   124 eV – 3 eV          
|-
| [[Visible light]] ||  400&nbsp;nm – 750&nbsp;nm || 750 THz – 400 THz ||   3 eV – 1.7 eV        
|-
| [[Infrared]]      ||  750&nbsp;nm – 1&nbsp;mm   || 400 THz – 300&nbsp;GHz ||   1.7 eV – 1.24 [[milli|m]]eV 
|- style="background:#ccffcc;"
| {{strong|Microwave}}  ||    1&nbsp;mm – 1&nbsp;m    || 300&nbsp;GHz – 300&nbsp;MHz || 1.24 meV – 1.24 [[Micro-|μ]]eV
<!-- Radio waves _include_ microwaves, so following ranges overlap those above: -->
|-
| [[Radio waves|Radio]] || ≥ 1&nbsp;m || ≤ 300&nbsp;MHz || ≤ 1.24 μeV
|}
In descriptions of the [[electromagnetic spectrum]], some sources classify microwaves as radio waves, a subset of the radio wave band, while others classify microwaves and radio waves as distinct types of radiation.<ref name="Hitchcock" /> This is an arbitrary distinction.

=== Frequency bands ===
Bands of frequencies in the microwave spectrum are designated by letters.  Unfortunately, there are several incompatible band designation systems, and even within a system the frequency ranges corresponding to some of the letters vary somewhat between different application fields.<ref name="Microwaves101">{{cite encyclopedia
  | title = Frequency Letter bands
  | encyclopedia = Microwave Encyclopedia
  | publisher = Microwaves101 website, Institute of Electrical and Electronics Engineers (IEEE)
  | date = 14 May 2016
  | url = https://www.microwaves101.com/encyclopedia/588-frequency-letter-bands
  | access-date = 1 July 2018}}</ref><ref name="Golio2">{{cite book
 | last1  = Golio
 | first1 = Mike
 | last2  = Golio
 | first2 = Janet
 | title  = RF and Microwave Applications and Systems
 | publisher = CRC Press
 | date   = 2007
 | pages  = 1.9–1.11
 | url    = https://books.google.com/books?id=fNJLcL1LBpEC&q=Microwave+letter+bands&pg=SL9-PA9
 | isbn   = 978-1420006711
 }}</ref>  The letter system had its origin in World War 2 in a top-secret U.S. classification of bands used in radar sets; this is the origin of the oldest letter system, the IEEE radar bands.   One set of microwave frequency bands designations by the [[Radio Society of Great Britain]] (RSGB), is tabulated below:
{{MWband}}
{| class="wikitable nowrap"
|+ Microwave frequency bands
! Designation !! Frequency range !! Wavelength range !! Typical uses
|-
| [[L band]] || 1 to 2&nbsp;GHz || 15&nbsp;cm to 30&nbsp;cm
|style="white-space:normal;"| military telemetry, GPS, mobile phones (GSM), amateur radio
|-
| [[S band]] || 2 to 4&nbsp;GHz || 7.5&nbsp;cm to 15&nbsp;cm
|style="white-space:normal;"| weather radar, surface ship radar, some communications satellites, microwave ovens, microwave devices/communications, radio astronomy, mobile phones, wireless LAN, Bluetooth, ZigBee, GPS, amateur radio
|-
| [[C band (IEEE)|C band]] || 4 to 8&nbsp;GHz || 3.75&nbsp;cm to 7.5&nbsp;cm
|style="white-space:normal;"| long-distance radio telecommunications, wireless LAN, amateur radio
|-
| [[X band]] || 8 to 12&nbsp;GHz || 25&nbsp;mm to 37.5&nbsp;mm
|style="white-space:normal;"| satellite communications, radar, terrestrial broadband, space communications, amateur radio, molecular rotational spectroscopy
|-
| [[Ku band|K<sub>u</sub> band]] || 12 to 18&nbsp;GHz || 16.7&nbsp;mm to 25&nbsp;mm
|style="white-space:normal;"| satellite communications, molecular rotational spectroscopy
|-
| [[K band (IEEE)|K band]] || 18 to 26.5&nbsp;GHz || 11.3&nbsp;mm to 16.7&nbsp;mm
|style="white-space:normal;"| radar, satellite communications, astronomical observations, automotive radar, molecular rotational spectroscopy
|-
| [[Ka band|K<sub>a</sub> band]] || 26.5 to 40&nbsp;GHz || 5.0&nbsp;mm to 11.3&nbsp;mm
|style="white-space:normal;"| satellite communications, molecular rotational spectroscopy
|-
| [[Q band]] || 33 to 50&nbsp;GHz || 6.0&nbsp;mm to 9.0&nbsp;mm
|style="white-space:normal;"| satellite communications, terrestrial microwave communications, radio astronomy, automotive radar, molecular rotational spectroscopy
|-
| [[U band]] || 40 to 60&nbsp;GHz || 5.0&nbsp;mm to 7.5&nbsp;mm
|style="white-space:normal;"|
|-
| [[V band]] || 50 to 75&nbsp;GHz || 4.0&nbsp;mm to 6.0&nbsp;mm
|style="white-space:normal;"| millimeter wave radar research, molecular rotational spectroscopy and other kinds of scientific research
|-
| [[W band]] || 75 to 110&nbsp;GHz || 2.7&nbsp;mm to 4.0&nbsp;mm
|style="white-space:normal;"| satellite communications, millimeter-wave radar research, military radar targeting and tracking applications, and some non-military applications, automotive radar
|-
| [[F band (waveguide)|F band]] || 90 to 140&nbsp;GHz || 2.1&nbsp;mm to 3.3&nbsp;mm
|style="white-space:normal;"| SHF transmissions: Radio astronomy, microwave devices/communications, wireless LAN, most modern radars, communications satellites, satellite television broadcasting, [[Direct broadcast satellite|DBS]], amateur radio
|-
| [[D band (waveguide)|D band]] || 110 to 170&nbsp;GHz || 1.8&nbsp;mm to 2.7&nbsp;mm
|style="white-space:normal;"| EHF transmissions: Radio astronomy, high-frequency microwave radio relay, microwave remote sensing, amateur radio, directed-energy weapon, millimeter wave scanner
|}

Other definitions exist.<ref>See {{cite web |url=http://www.radioing.com/eengineer/bands.html |title=eEngineer – Radio Frequency Band Designations |publisher=Radioing.com |access-date=2011-11-08 }}, {{cite web |author=PC Mojo – Webs with MOJO from Cave Creek, AZ |url=http://www.microwaves101.com/encyclopedia/letterbands.cfm |title=Frequency Letter bands – Microwave Encyclopedia |publisher=Microwaves101.com |date=2008-04-25 |access-date=2011-11-08 |archive-url=https://web.archive.org/web/20140714171156/http://www.microwaves101.com/ENCYCLOPEDIA/letterbands.cfm |archive-date=2014-07-14 |url-status=dead }}, [http://www.jneuhaus.com/fccindex/letter.html Letter Designations of Microwave Bands].</ref>

{{anchor|P band}}The term P band is sometimes used for [[Ultra high frequency|UHF]] frequencies below the L band but is now obsolete per IEEE Std 521.

When radars were first developed at K band during World War 2, it was not known that there was a nearby absorption band (due to water vapor and oxygen in the atmosphere). To avoid this problem, the original K band was split into a lower band, K<sub>u</sub>, and upper band, K<sub>a</sub>.<ref name="test">Skolnik, Merrill I. (2001) ''Introduction to Radar Systems'', Third Ed., p. 522, McGraw Hill. [https://archive.org/details/IntroductionToRadarSystems 1962 Edition full text]</ref>