Ku band
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- The correct title of this article is Ku band. It features superscript or subscript characters that are substituted or omitted because of technical limitations.
The Ku band (pronounced "kay-yoo") is a portion of the electromagnetic spectrum in the microwave range of frequencies. This symbol refers to "K-under" — in other words, the band directly below the K-band. In radar applications, it ranges from 12 to 18 GHz according to the formal definition of radar frequency band nomenclature in IEEE Standard 521-2002. [1][2]
Ku band is primarily used for satellite communications, most notably NASA's Tracking Data Relay Satellite used for both space shuttles, and ISS communications. Ku band satellites are also used for backhauls and particularly for satellite from remote locations back to a television network's studio for editing and broadcasting. The band is split into multiple segments that vary by geographical region by the International Telecommunication Union (ITU). NBC was the first television network to uplink a majority of its affiliate feeds via Ku band in 1983.
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[edit] Segments and regions
[edit] The Americas
Segments in most of the Americas are represented by (ITU Region 2) and they are, the 11.7 to 12.2 GHz (Local Oscillator Frequency (LOF) 10.750 GHz) band is allocated to the FSS (fixed service satellite, uplink 14.0 to 14.5 GHz). There are more than 22 FSS Ku-band satellites orbiting over North America, each carrying 12 to 24 transponders, 20 to 120 watts per transponder, and requiring a 0.8-m to 1.5-m antenna for clear reception.
The 12.2 to 12.7 GHz (LOF 11.250 GHz) segment is allocated to the BSS (broadcasting satellite service). BSS/DBS direct broadcast satellites normally carry 16 to 32 transponders of 27 MHz bandwidth running at 100 to 240 watts of power, allowing the use of receiver antennas as small as 18 inches (450 mm).
[edit] 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 GHz bands are allocated to the FSS (fixed satellite service, uplink 14.0 to 14.5 GHz).
In Europe Ku band is used from 10.7 to 12.75 GHz (LOF Low 9.750 GHz, LOF High 10.600 GHz) for direct broadcast satellite services like SES Astra.
The 11.7 to 12.5 GHz segment is allocated to the BSS (broadcasting satellite service).
[edit] Australia
Australia is part of ITU Region 3 and the Australian regulatory environment provides a class license that covers downlinking from 12.25GHz to 12.75GHz and uplinking from 14.0GHz to 14.5GHz.
[edit] Others
Other ITU allocations have been made within the Ku band to the fixed service (microwave towers), radio astronomy service, space research service, mobile service, mobile satellite service, radiolocation service (radar), amateur radio service, and radionavigation. However, not all of these services are actually operating in this band and others are only minor users.
[edit] Indonesia
The ITU has categorized Indonesia as Region P, countries with very high rain precipitation. This statement has made many people unsure about using Ku-band (11 – 18 GHz) in Indonesia. If frequencies higher than 10 GHz are used in a heavy rain area, a decrease in communication availability 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, in addition to 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 Ku-band can be applied in Indonesia.
The use of the Ku-band for satellite communications in tropical regions like Indonesia is becoming more frequent. Several satellites above Indonesia have Ku-band transponders, and even Ka-band transponders. Newskies (NSS 6), launched in December 2002 and positioned at 95° East, contains only Ku-band transponders with a footprint on Indonesia (Sumatra, Java, Borneo, Celebes, Bali, Nusa Tenggara, Moluccas). The iPSTAR satellite, launched in 2004 also uses Ku band footprints. Measat has named the Ku-band footprint directed towards Indonesia Ku-band for Indonesi. Measat 4 plans to cover the whole of Indonesia from West to East. This satellite will be launched by Malaysia in 2007.
[edit] Advantages
Compared with C-band, Ku 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 dish’s size can decrease.[3]
The Ku band also offers a user more flexibility. A dish smaller size and a Ku band system’s freedom from terrestrial operations simplifies finding a suitable dish site. Ku band is generally cheaper and enables smaller antennas (both because of the higher frequency and a more focused beam).[4] Kuband is also less vulnerable to rain fade than the Ka-band frequency spectrum.
[edit] Disadvantages
There are, however, some disadvantages of Ku band system. Especially at frequencies higher than 10 GHz in heavy rain fall areas, a noticeable degradation occurs, due to the problems caused by and proportional to the amount of rainfall (commonly known as "rain fade").[5] This problem can be mitigated, however, by deploying an appropriate link budget strategy when designing the satellite network, and allocating a higher power consumption to reduce rain fade loss. The Ku band is not only used for television transmission, which some sources imply, but also very much for digital data transmission via satellites, and for voice/audio transmissions.
The higher frequency spectrum of the Ku band is particularly susceptible to signal degradation, considerably more so than C-band satellite frequency spectrum. A similar phenomenon, called "snow fade" (where snow or ice accumulation significantly alters the focal point of a dish) can also occur during winter precipitation. Also, the Kuband satellites typically require considerably more power to transmit than the C-band satellites. Under both "rain fade" and "snow fade" conditions, Ka and Ku band losses can be marginally (but significantly) reduced using super-hydrophobic Lotus effect coatings.
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[edit] References
- ^ IEEE Std 521 - 2002 URL only available to IEEE members
- ^ Note that in the band 11.2 - 12 GHz the working definitions of Ku band and X band overlap; satellite communications engineers would generally regard frequencies above 11.2 GHz as being part of the Ku band)
- ^ Mirabito, M.,& Morgenstern, B. (2004). Satellites: Operations and Applications. The New Communication Technologies (fifth edition). Burlington: Focal Press.
- ^ Satellite Communications: Advantage and Disadvantages
- ^ What is Ku band?
[edit] External links
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