View source for Ku band

{{Short description|Range of radio frequencies from 11-20 GHz}}
{{DISPLAYTITLE:K<sub>u</sub> band}}
{{multiple issues |{{Globalize|date=July 2014}} {{more citations needed|date=July 2014}} }}
{{MWband
| name = IEEE K<sub>u</sub> band
| freq = 12–18 [[Hertz|GHz]]
| bands = {{hlist|item_style=white-space:nowrap; |[[J band (NATO)|J]] (NATO) |[[Super high frequency|SHF]] (ITU)}}
| wave = 2.5–1.67 [[Meter|cm]]
}}

The '''K<sub>u</sub> band''' ({{IPAc-en|ˌ|k|eɪ|ˈ|j|uː}}) is the  portion of the [[electromagnetic spectrum]] in the [[microwave]] range of frequencies from 12 to 18&nbsp;[[gigahertz]] (GHz).  The symbol is short for "K-under" (originally {{langx|de|Kurz-unten}}), because it is the lower part of the original [[K band (NATO)|NATO K band]], which was split into three bands (K<sub>u</sub>, [[K band (IEEE)|K]], and [[Ka band|K<sub>a</sub>]])  because of the presence of the atmospheric [[water vapor]] resonance peak at 22.24&nbsp;GHz, (1.35&nbsp;cm) which made the center unusable for long range transmission.  In radar applications, it ranges from 12 to 18&nbsp;[[Hertz|GHz]] according to the formal definition of radar frequency band nomenclature in IEEE Standard 521–2002.<ref>[https://ieeexplore.ieee.org/document/1160089/;jsessionid=0A8FCFADFCE36B3BA0A6FB54F88A2849?tp=&isnumber=26011&arnumber=1160089&punumber=8332 IEEE Std 521 - 2002] URL only available to IEEE members</ref><ref>Note that in the band 11.2–12&nbsp;GHz the ''working'' definitions of K<sub>u</sub> band and [[X band]] overlap; satellite communications engineers would generally regard frequencies above 11.2&nbsp;GHz as being part of the K<sub>u</sub> band.</ref>

K<sub>u</sub> band is primarily used for [[satellite communication]]s, most notably the downlink used by [[direct broadcast satellite]]s to broadcast [[satellite television]], and for specific applications such as [[NASA]]'s [[Tracking Data Relay Satellite]] used for [[International Space Station]] (ISS) communications and [[SpaceX]] [[Starlink]] satellites.<ref>{{Cite web|url=https://spacenews.com/spacex-seeks-fcc-permission-for-operating-all-first-gen-starlink-in-lower-orbit/|title=SpaceX seeks FCC permission for operating all first-gen Starlink in lower orbit|date=2020-04-21|website=SpaceNews.com|language=en-US|access-date=2020-04-23}}</ref> K<sub>u</sub> band satellites are also used for [[backhaul (telecommunications)|backhaul]]s and particularly for satellite from remote locations back to a [[television]] network's studio for editing and [[broadcasting]].  The band is split by the [[International Telecommunication Union]] (ITU) into multiple segments that vary by geographical region. [[NBC]] was the first television network to uplink a majority of its affiliate feeds via K<sub>u</sub> band in 1983.

Some frequencies in this radio band are employed in [[radar gun]]s used by law enforcement to detect vehicles speeding, especially in Europe.<ref>[http://www.crutchfield.com/S-IRLWckuTGNf/learn/learningcenter/car/radar_glossary.html Radar Detectors Glossary]</ref>

==Segments and regions==
[[Image:SuperDISH121.jpg|thumb|One use of the band is [[direct-broadcast satellite television]].  A [[satellite dish]] on a residence, which receives satellite television channels over a K<sub>u</sub> band microwave beam from a broadcast [[communications satellite]] in a [[geostationary orbit]] 35,700 kilometres (22,000 miles) above the Earth.]]

===America===
Segments in most of North and South America are represented by [[ITU Region]] 2 from 11.7 to 12.2&nbsp;GHz ([[Local Oscillator]] Frequency (LOF) 10.75 to 11.25&nbsp;GHz), allocated to the FSS ([[fixed satellite service]]), [[uplink]] from 14.0 to 14.5&nbsp;GHz. There are more than 22 FSS K<sub>u</sub> band satellites orbiting over North America, each carrying 12 to 48 [[Transponder (Satellite communications)|transponders]], 20 to 120 [[watt]]s per transponder, and requiring a 0.8-m to 1.5-m antenna for clear reception.

The 12.2 to 12.7&nbsp;GHz (LOF 11.25 to 11.75&nbsp;GHz) segment is allocated to the BSS ([[broadcasting satellite service]]). BSS (DBS [[direct broadcast satellite]]s) normally carry 16 to 32 transponders of 27&nbsp;[[Megahertz|MHz]] bandwidth running at 100 to 240 watts of power, allowing the use of receiver antennas as small as 18&nbsp;inches (450&nbsp;mm).

===Europe and Africa===
Segments in those regions are represented by ITU Region 1, and they are the 11.45 to 11.7 and 12.5 to 12.75&nbsp;GHz bands are allocated to the FSS ([[fixed satellite service]], [[uplink]] 14.0 to 14.5&nbsp;GHz). In Europe K<sub>u</sub> band is used from 10.7 to 12.75&nbsp;GHz (LOF Low 9.75&nbsp;GHz, LOF High 10.6&nbsp;GHz) for [[direct broadcast satellite]] services such as those carried by the [[SES Astra|Astra]] satellites. The 11.7 to 12.5&nbsp;GHz segment is allocated to the BSS ([[broadcasting satellite service]]).

===Australia===
Australia is part of ITU Region 3 and the Australian regulatory environment provides a class license that covers downlinking from 11.70&nbsp;GHz to 12.75&nbsp;GHz and uplinking from 14.0&nbsp;GHz to 14.5&nbsp;GHz.<ref>{{cite web|url=http://www.comlaw.gov.au/Details/F2012C00166|access-date=2016-07-06|date=2012-03-21|title=Radiocommunications (Communication with Space Object) Class Licence 1998|publisher=Australian Government|website=Federal Register of Legislation}}</ref>

===Indonesia===
The [[International Telecommunication Union|ITU]] has categorized [[Indonesia]] as Region P, countries with very high rain precipitation. This statement has made many people unsure about using K<sub>u</sub>-band (11 – 18&nbsp;GHz) in Indonesia.  Using frequencies higher than 10&nbsp;GHz in a heavy rain area usually gives poor results. This problem can be solved by using an appropriate [[link budget]] when designing the wireless communication link. Higher power can overcome the loss to [[rain fade]].

Measurements of rain attenuation in Indonesia have been done for satellite communication links in Padang, Cibinong, Surabaya and Bandung. The DAH Model for rain attenuation prediction is valid for Indonesia, as is the ITU model. The DAH model has become an ITU recommendation since 2001 (Recommendation No. ITU-R P.618-7). This model can create a 99.7% available link so that K<sub>u</sub>-band can be applied in Indonesia.

Use of the K<sub>u</sub>-band for satellite communications in tropical regions like Indonesia is becoming more frequent. Several satellites above Indonesia have K<sub>u</sub>-band [[transponder]]s, and even [[Ka band|K<sub>a</sub> band]] transponders. [[NSS 6]], launched in December 2002 and positioned at 95° East, contains only K<sub>u</sub>-band transponders with a footprint on Indonesia ([[Sumatra]], [[Java]], [[Borneo]], [[Sulawesi|Celebes]], [[Bali]], [[Nusa Tenggara]], [[Moluccas]]). NSS 6 is intended to be replaced by [[SES-12]] at the same location, which launched in June 2018 and carries 54 K<sub>u</sub>-band transponders. The [[Thaicom 4|IPSTAR 1]] satellite, launched in 2004 also uses K<sub>u</sub> band footprints. Other satellites that provides K<sub>u</sub> band covers Indonesia are [[MEASAT-3b]], [[JCSAT-4B]], [[AsiaSat 5]], [[ST-2]], [[Chinasat]] 11, [[ABS-2|Koreasat 8/ABS-2]], [[SES-8]], [[SES-9]], [[Telkom-3S]], and [[Nusantara Satu]].

===Others===
Other ITU allocations have been made within the K<sub>u</sub> band to the fixed service (microwave towers), radio astronomy service, space research service, mobile service, mobile satellite service, radiolocation service (radar), [[Amateur radio|amateur radio service]], and radionavigation.  However, not all of these services are actually operating in this band and others are only minor users.

==Advantages==
Compared with [[C band (IEEE)|C-band]], K<sub>u</sub> band is not similarly restricted in power to avoid interference with terrestrial microwave systems, and the power of its uplinks and downlinks can be increased.  This higher power also translates into smaller receiving dishes and points out a generalization between a satellite's transmission and a dish's size.  As the power increases, the size of an antenna's dish will decrease.<ref>{{cite book|last1=Mirabito|first1=M|last2=Morgenstern|first2=B|year=2004 |title=Satellites: Operations and Applications. The New Communication Technologies|edition=5|location=Burlington|publisher=Focal Press.|isbn=978-0240805863}}</ref>{{page needed|date=July 2016}} This is because the purpose of the dish element of the antenna is to collect the incident waves over an area and focus them all onto the antenna's actual receiving element, mounted in front of the dish (and pointed back towards its face); if the waves are more intense, fewer of them need to be collected to achieve the same intensity at the receiving element.

A major attraction of the band over lower frequency microwave bands is that the shorter wavelengths allow sufficient angular resolution to separate the signals of different communication satellites to be achieved with smaller terrestrial [[parabolic antenna]]s.   From the [[Angular resolution#The_Rayleigh_criterion|Rayleigh criterion]], the diameter of a parabolic dish required to create a radiation pattern with a given angular [[FWHM|beamwidth]] ([[antenna gain|gain]]) is proportional to the [[wavelength]], and thus inversely proportional to the frequency.   At 12&nbsp;GHz a 1-meter dish is capable of focusing on one satellite while sufficiently rejecting the signal from another satellite only 2 degrees away. This is important because satellites in FSS (Fixed Satellite Service) service (11.7-12.2&nbsp;GHz in the U.S.) are only 2 degrees apart.  At 4&nbsp;GHz (C-band) a 3-meter dish is required to achieve this narrow angular resolution.  Note the inverse linear correlation between dish size and frequency.  For K<sub>u</sub> satellites in DBS (Direct Broadcast Satellite) service (12.2-12.7&nbsp;GHz in the U.S.) dishes much smaller than 1-meter can be used because those satellites are spaced 9 degrees apart.  As power levels on both C and K<sub>u</sub> band satellites have increased over the years, dish beam-width has become much more critical than gain.

The K<sub>u</sub> band also offers a user more flexibility. A smaller dish size and a K<sub>u</sub> band system's freedom from terrestrial operations simplifies finding a suitable dish site. For the end users K<sub>u</sub> band is generally cheaper and enables smaller antennas (both because of the higher frequency and a more focused beam).<ref>[http://en.allexperts.com/q/Satellite-Communications-2436/Advantage-Disadvantages-1.htm Satellite Communications: Advantage and Disadvantages] {{webarchive|url=https://web.archive.org/web/20071023070212/http://en.allexperts.com/q/Satellite-Communications-2436/Advantage-Disadvantages-1.htm |date=2007-10-23 }}</ref> K<sub>u</sub> band is also less vulnerable to rain fade than the K<sub>a</sub> band frequency spectrum.

==Disadvantages==
There are, however, some disadvantages of the K<sub>u</sub> band system. Around 10&nbsp;GHz is the absorption peak due to orientation relaxation of molecules in liquid water.<ref>Martin Chaplin: [http://www1.lsbu.ac.uk/water/microwave_water.html ''Water and Microwaves''] {{Webarchive|url=https://web.archive.org/web/20190729022932/http://www1.lsbu.ac.uk/water/microwave_water.html |date=2019-07-29 }}.</ref> Above 10&nbsp;GHz, [[Mie scattering]] takes over. The effect is a noticeable degradation, commonly known as [[rain fade]], during heavy rain (100&nbsp;mm/h).<ref>TECH-FAQ: [http://www.tech-faq.com/ku-band.shtml Ku band].</ref> This problem can be mitigated by transmitting a higher powered signal from the satellite to compensate. Therefore, the K<sub>u</sub> band satellites typically require considerably more power to transmit than the C-band satellites.

Another weather-caused degradation called "snow fade" is not specific to the K<sub>u</sub> band. It is due to snow or ice accumulation on a dish significantly altering its focal point.

The satellite operator's Earth station antenna requires more accurate position control when operating at K<sub>u</sub> band due to its much narrower beam focus compared to C band for a dish of a given size. Position feedback accuracies are higher and the antenna may require a closed loop control system to maintain position under wind loading of the dish surface.

==See also==
* [[Multifunction Advanced Data Link]]

==References==
{{Reflist}}

==External links==
*[http://www.unwantedemissions.com Frequency allocation information, mostly for U.S.]
*[http://www.ntia.doc.gov/osmhome/allochrt.pdf Spectrum allocation chart]

{{Radio spectrum}}
{{Electromagnetic spectrum}}
{{Wireless video}}
{{Telecommunications}}
{{Audio broadcasting}}

[[Category:Microwave bands]]
[[Category:Satellite broadcasting]]