X band The X band is the designation for a band of frequencies in the microwave radio region of the electromagnetic spectrum. In some cases, such as in communication engineering, the frequency range of the X band is rather indefinitely set at approxim ...

or SHF

Satellite Communication A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. C ...

is widely used by military forces for beyond line of sight communications. X band is used because it provides a compromise between the characteristics of different frequency bands which is particularly suited to the needs of military users. The characteristics include interference and rain resilience, terminal size, data rates, remote coverage and whether it is reserved for governmental use.

Characteristics of the SHF frequency band

Frequency

x Band Satellite Communication operates in the part of the

Super High Frequency Super high frequency (SHF) is the ITU designation for radio frequencies (RF) in the range between 3 and 30 gigahertz (GHz). This band of frequencies is also known as the centimetre band or centimetre wave as the wavelengths range from one to ...

(SHF) spectrum which is designated by the

International Telecommunication Union The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...

(ITU) for satellite communication, which is those frequencies in the range 7.25 GHz to 7.75 GHz (Space to Earth) and 7.9 GHz to 8.4 GHz (Earth to Space). The ITU

Frequency allocation Frequency allocation (or spectrum allocation or spectrum management) is the allocation and regulation of the electromagnetic spectrum into radio frequency bands, normally done by governments in most countries. Because radio propagation does no ...

defines the primary use of this spectrum as

Fixed satellite service Fixed-satellite service (short: FSS | also: fixed-satellite radiocommunication service) is – according to ''article 1.21'' of the International Telecommunication Union's (ITU) Radio Regulations (RR) – defined as ''A radiocommunication se ...

(FSS) and a portion to Mobile Satellite Services (MSS), primarily used for ship based satellite communications. UK Frequency Allocation Table (UK FAT) along with other

NATO The North Atlantic Treaty Organization (NATO, ; french: Organisation du traité de l'Atlantique nord, ), also called the North Atlantic Alliance, is an intergovernmental military alliance between 30 member states – 28 European and two No ...

countries and some other countries’ (but not all) national frequency allocations tables, have an additional note detailing the primary allocation for government use. It is important to note that the allocation of these frequencies and services is for government use and not, as commonly stated, military use. The ITU and the UK

Ofcom The Office of Communications, commonly known as Ofcom, is the government-approved regulatory and competition authority for the broadcasting, telecommunications and postal industries of the United Kingdom. Ofcom has wide-ranging powers acros ...

considers military use as just one part of government use.

Rain resilience

X band is below those frequencies which are severely affected by

Rain Fade Rain fade refers primarily to the absorption (optics), absorption of a microwave radio frequency (RF) signal by atmospheric rain, snow, or ice, and losses which are especially prevalent at frequencies above 11 GHz. It also refers to the degradation ...

, therefore X band provides extremely good rain resilience unlike higher frequencies such as Ku or Ka which are also used for satellite communication. This allows extremely high link availability, in some cases as high as 99.9%

>4° separation between satellites

X band satellites typically have at least 4° separation between satellites, therefore there is less chance of adjacent satellite interference (ASI) and higher power density carriers allowed.

Terminal size v data rates

As with any satellite communication link, the data rate that can be achieved with a terminal is dependent on the gain of the

parabolic antenna A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or pa ...

. Antenna gain increases with the square of the ratio of aperture width to wavelength. Therefore, for a fixed antenna size the gain, and hence the achievable data rate increases with frequency. Thus X band provides data rates which are much higher than can be achieved with UHF, L band, or C band. The achievable data rates will approach those achievable with Ku band, the exact values will depend on other link parameters (satellite power, link margin, modulation scheme, etc.). Therefore, X band provides a good compromise between terminal size and data rates while maintaining resilience to rain fade. Data rates of 10Mbit/s are achievable to a 45 cm antenna without interfering with adjacent satellites.

Remote and maritime coverage

X band spot beams typically have a diameter of 1000 km or more. This is the result of the frequency and the size of

Parabolic antenna A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or pa ...

which can be accommodated inside satellite launch vehicles. This means that a single beam is able to be steered to cover an entire region of interest. X band satellites also have an earth cover or global beam providing coverage of the entire planet that is visible from the satellite. This is in contrast to satellites in commercial bands which typically provide fixed beams for areas of high density of users. Therefore, X band satellites are able to support users in remote areas with little or no infrastructure and in mid ocean away from land and shipping lanes.

Characteristics of SHF Satcom systems

SHF Satcom systems often possess features designed to meet the needs of military users and to counter threats to the system. Features include * Steerable beams * High power spectral density * Protection against nuclear events and space weather * Military grade cryptography on the telecommand system * Protection against laser threats * Military specification control facilities * Protection against jamming attacks * Flexible connectivity

Components of SHF Satcom systems

Like other Satellite Communications systems, X band satellite communication systems comprise the following segments: *

Satellite space segment The space segment of an artificial satellite system is one of its three operational components (the others being the user and ground segments). It comprises the satellite or satellite constellation and the uplink and downlink satellite links. The ...

: the satellite which comprises the platform and the payload * Control Segment: the ground equipment to control the satellite * Anchor facilities: while mesh configurations are possible, most X band satcom systems use anchor facilities to exploit the link budget benefits from large antennas and to provide terrestrial connectivity * Network management: the facilities to manage the communication network, in particular the baseband elements * User terminals: the terminals used by deployed users to connect to the satellite system. User terminals may be interoperable with several different X band systems. User terminals are adapted to the requirements of the environment in which they operate.

Satellite communication systems operating at X band

Skynet

The Skynet fleet of satellites are owned and operated by Airbus Defence & Space who hold a long term concession for beyond line of sight communications with the UK MOD. The fleet includes four high performance Skynet 5 satellites with 160W TWTAs providing up to 8W/MHz and an active receive antenna capable of creating multiple uplink beam patterns. The Skynet fleet also includes older Skynet 4 satellites which are beyond their original design life and in inclined orbits, these orbits enable them to provide communications to arctic and Antarctic regions. In addition to SHF capacity the Skynet satellites also have UHF capacity.

Wideband Global SATCOM system (WGS)

The WGS system is a constellation of military communications satellites procured by the U.S. Air Force MILSATCOM Systems Directorate at Los Angeles Air Force Base (AFB). Each WGS satellite provides capacity in both the X and Ka frequency bands. Each WGS satellite is digitally channelized and transponded. International partners participating on the program are Australia, Canada, Denmark, Luxembourg, The Netherlands and New Zealand.

XTAR-EUR

The

XTAR-EUR The XTAR-EUR is a communication satellite developed by Spain and the United States and in order to provide a secure channel over the Indian Ocean. It was originally operated by XTAR and Hisdesat. In year 2020 Hisdesat bought 100% stake on the sa ...

satellite is owned and operated by XTAR LLC and

Hisdesat Hisdesat (, 'Hisdesat Strategic Services') is a Spanish company created in 2001 by Hispasat (43%), Ingeniería y Servicios Aeroespaciales (30%), EADS CASA (15%, now Airbus), Indra Sistemas (7%) and SENER (5%) with initial investment of 415 mill ...

. It was launched in February 2005 and is positioned at 29 degrees east. XTAR-EUR has 100W, 72 MHz transponders

Spainsat

SpainSat Spainsat is a Spanish telecommunications satellite used for military and government communications. It allows telecommunications the different missions of the Spanish Armed forces abroad by providing coverage on a wide area of the world ranging ...

is owned by

. SpainSat was launched in March 2006 and is positioned at 29 degrees west. Spainsat has an X-Band payload with 100W, 72 MHz transponders. It also has Ka band capacity.

Sicral

SICRAL (Sistema Italiano per Comunicazioni Riservate ed Allarmi) is Italy’s satellite system for military communications. The SICRAL 1 satellite was launched in 2001 and the

SICRAL 1B SICRAL 1B is a military communications satellite built by Thales Alenia Space for Italian Armed Forces. It is a dual-use spacecraft: Telespazio will use some of the satellite's transmission capacity and some will be used by the Italian defense min ...

satellite was launched in 2009.

Syracuse

Syracuse III (système de radiocommunications utilisant un satellite) is the military satellite communication system of the French ministry of Defence. Syracuse 3A was launched in 2005 and Syracuse 3B was launched in 2006.

Anik G1

Anik G1 was launched in April 2013, and includes a 3-transponder, global-beam X-band payload, operating from 107.3°W.

DC-MS Series 2

DC-MS Series 2 consists of 2 triple-transponder global-beam X-band payload, operated by Delta Communications. DC-MS Series 2 was launched in January 2014.

NATO SATCOM Post-2000

The NATO X Band satellite system consists of a NATO owned

ground segment A ground segment consists of all the ground-based elements of a space system used by operators and support personnel, as opposed to the space segment and user segment. The ground segment enables management of a spacecraft, and distribution of p ...

with capacity leased from a consortium formed by the British, French and Italian governments.

References

{{Reflist

External links

* SATELLITE COMMUNICATIONS (SATCOM) https://fas.org/spp/military/docops/army/ref_text/chap07b.htm Communications satellites Military communications