Intermodulation and bit-error ratio performance of a Ku-band multibeam high-power phased array

The overall transmission quality of a communications satellite utilizing a multibeam phased array antenna system is dependent upon the uniformity of the components within the communications payload. This system dependency is no greater in any component than in the solid-state power amplifier (SSPA) modules. Significant variations in the individual characteristics of the SSPAs have an impact on all the signals transmitted by the satellite. Moreover, as the amount of traffic being handled by the satellite increases, the available power per channel is reduced. The result is a degradation in the overall quality of the communications channels. A common measure of the quality of a digital communications link is the bit error ratio (BER) with respect to the carrier-to-noise ratio. Therefore, it is beneficial to perform an in-depth analysis for multiple, individually steerable beams vis-a-vis the intermodulation and BER characteristics in multiple signal scenarios. The paper includes results from both software simulation and laboratory measurements of a 24-element Ku-band active phased array under a variety of operational scenarios. The resulting data achieves a mutual validation of COMSATs software simulation tools as well as the multibeam phased array concept as applied to communications satellite systems.