The prevalent use of unmanned vehicles in military and civilian applications requires the existence of robust and high throughput communication with airborne platforms. Real channel measurements are conducted and the analysis supports the use of MIMO communications for such applications due to its potential throughput advantage. Unique challenges and the ways to address them are described in detail. In particular, the lack of scattering and the blockage of line of sight may lead to rank deficient channel matrices, which are exacerbated due to the absence of channel state information at the transmitter. A variable rate MIMO scheme is proposed to overcome these challenges in order to realize the promising throughput gain afforded by MIMO communication.
In 1999 an airbome Global Broadcast Service (GBS) and MILSTAR receive antenna was evaluated and successfully demonstrated in flight, atop an AFRLAFG, C-135 SATCOM test aircraft. This Luneburg lens antenna received 20 GHz Left Hand Circular Polarization (LHCP) from a GBS terminal onboard the UFO-9 satellite and 20 GHz Right Hand Circular Polarization (RHCP) from a MILSTAR satellite. A detailed unclassiJed paper entitled "Airbome Demonstration of MIL-STAR and GBS Receive Capability Using a Single Antenna" has been publishecf. Phase II of this antenna adds a 44 GHz 'Tx capabilio. This fully mechanically scanned antenna will still provide, f 80 degree coverage while rotating 360 degrees in azimuth. The hemispherical lens height was increased from 3 inches to 4 inches to increase gain and the lenses were redesigned with more shells to increase the eficie.4 for transmission at 44 GHz. A new feeder network was designed with 20 and 44 GHz homs to allow reception of 23.5 Mbps from the GBS terminal on the UFO satellites and to provide a medium data rate (MDR) transmidreceive (7wRx) capability with the planned Milstar N satellite. The 20/44 GHz antenna components, including Laneburg lens improvements and temperature test results will be presented
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