Cumulative system-level qualification of mobile satellite communications antennas through aggregate subsystem-level tests

The U.S. Army and other purchasers of mobile SATCOM “on-the-move” (SOTM) antennas often acquired their first units as commercial-off-the-shelf items, developed by ambitious vendors in a “build it and they will buy it” environment. Initial evaluations were mostly qualitative (It worked well or it didn't), as many early users were completely satisfied to have this capability at all. Quantitative assessments were often limited to end-to-end data throughput rates. Information on pointing performance was especially difficult to ascertain, as test conditions were too complicated and non-repeatable to clearly isolate pointing performance from the many other error sources (terrain, driving speed, vehicle characteristics, weather, waveform, etc). Customers have steadily become more sophisticated, such that these antennas are now often purchased against detailed customer specifications which include specific requirements for the various aspects of pointing performance, such as stabilization, tracking, alignment, and cross-polarization. Determining and isolating antenna pointing performance from the other error sources listed above is part of FCC licensing under the Vehicle Mounted Earth Station (VMES) rules recently issued, which specifically limits pointing error. An approach for cumulative system-level qualification of pointing performance through a combination of analysis, simulation, and subsystem testing is outlined. An emphasis is placed on methodologies that can be executed in a controlled environment while minimizing use of specialized test equipment. A case study is presented to illustrate the method.