Intermodulation suppression for transmit active phased array satellite antennas with multiple shaped beams

Active phased array antennas have, in general, low antenna efficiency driven by low SSPA (solid state power amplifier) efficiency. This is particularly true for transmit multibeam arrays where the SSPA has to be backed off to reduce the intermodulation (IM) power and thereby meeting the C/I (carrier-to-interference ratio) requirement within the coverage region on the ground. It is demonstrated theoretically that a transmit active phased array antenna with multiple shaped beams can be operated much more effectively by selecting different aperture phase distributions per beam. For an array with two beams, the required DC power has been reduced by 40% for the same minimum EIRP (effective isotropic radiated power), while the corresponding reduction for four beams is 50%. It is expected that this improvement may be slightly less if RMS excitation errors are included in the model. The new technique can be implemented without any extra hardware.