Intermodulation Analysis of FDMA Satellite Systems Employing Compensated and Uncompensated TWT´s

In a frequency-division multiple-access (FDMA) satellite communication system, the output power of the TWT (or FET) amplifier is backed from saturation to reduce the intermodulation distortion caused by AM/AM and AM/PM nonlinearities. The required amount of backoff can be considerable, wasting valuable satellite power, unless some scheme is used to compensate for these nonlinearities. A comparative study is presented for the effectiveness of three types of predistortion compensators: (1) a cuber predistortion linearizer, which is the simplest to build; (2) an AM/PM equalizer; and (3) an ideal linearizer, which is quite difficult to realize in practice.