Compensators for Bandpass Nonlinearities in Satellite Communications

The characteristics of optimum compensators for bandpass non-linearities are described. A predistortion compensator to reduce the nonlinear phase and envelope distortion at the output of a traveling-wave tube (TWT) is developed, and a possible implementation as a simple network of power law devices in cascade with the input to the TWT is given. The overall compensated characteristic of the TWT approximates that of a piecewise linear limiter with a small phase shift. A computer simulation shows that the compensated system yields 0.3 to 0.5-dB improvement in performance of a 2-phase coherent phase shift keying (CPSK) system over the uncompensated system.