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By Julian Nettlefold, Editor, BATTLESPACE

This is the first part of a two part Feature, the next will feature software radio systems

The growing use of beyond-line-of sight sensor and communications systems coupled to the development of more powerful and efficient satellites has meant that satcom rather than radio is becoming the system of choice for these applications in particular.

The success of the Skynet 5 Programme by Astrium which now has two birds up with one to go and the U.S. Wideband Gapfiller SATCOM system for which six birds are planned, one for Australia, has one bird up undergoing test prior to full deployment.

Both systems accommodate X and Ka bands. The growing use of X band which is a ‘Government only Band’ also negates the need for Governments to pay commercial rates on shared Ku band systems.

The Wideband Global SATCOM

The Wideband Global SATCOM (WGS) satellites are the key elements of a
high-capacity system that will provide a quantum leap in communications capabilities for the warfighter. WGS will support the DoD’s warfighting information exchange requirements, enabling execution of tactical command and control, communications, and computers; intelligence, surveillance, and reconnaissance (C4ISR); battle management; and combat support information. WGS will also augment the current Ka-band Global Broadcast Service (on UHF F/O satellites) by providing additional information broadcast capabilities. Each WGS can route 2.1 to 3.6 Gbps of data — providing more than 10 times the communications capacity of the predecessor DSCS III satellite. Using reconfigurable antennas and a digital channelizer, WGS also offers added flexibility to tailor coverage areas and to connect X-band and Ka-band users anywhere within the satellite field of view. The system provides tremendous operational flexibility and delivers the needed capacity, coverage, connectivity and control in support of demanding operational scenarios.

Boeing was awarded the WGS initial contract in January 2001 for the first three satellites plus the associated ground-based command and control elements. Integrated logistics, training, and sustaining engineering support are also provided by Boeing. The procuring agency is the U.S. Air Force Space Command’s MILSATCOM Systems Wing at Los Angeles AFB, California.

The WGS space segment will initially consist of three geostationary satellites operating over Pacific, Indian and Atlantic regions. Under a Block II contract, a fourth and fifth satellite are being procured to meet the warfighter’s evolving SATCOM bandwidth requirements, a sixth will be added for Austrlia. The Block II satellites will be similar to the three Block I satellites already in production and will add a radio frequency bypass capability designed to support airborne intelligence, surveillance and reconnaissance platforms requiring ultra-high bandwidth and data rates demanded by unmanned aerial vehicles.

WGS will provide transformational capabilities supporting government objectives for the Transformational Communications Architecture in the next decade and beyond.

Why X band?

The X band, ranging from 7 to 12.5 GHz (the 10.7-12.5 portion overlapping Ku band), with a standard downlink band of 7.25 to 7.75 GHz (uplink 7.9 to 8.4 GHz), is part of the microwave band of the electromagnetic spectrum. The term is also used informally to refer to the extended AM broadcast band. The typical local oscillator frequency of an X band LNB is 6300 MHz. X band is used by some communications satellites and for radars systems. The 3-cm radar spot-band ranges roughly from 5.2 to 10.9 GHz. X band radar has a variety of types. Some of these types are continuous-wave, pulsed, single-pole, dual-pole, SAR, or phased array. X band radar has various uses in civil, military and government institutions; in roles such as weather monitoring, air traffic control, maritime vessel traffic control, defense trackin

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