Simulation of the Effects of Q-Band Amplifier Nonlinearities on Non-Constant Envelope SATCOM Waveforms

Due to their higher spectral efficiency, non-constant envelope modulation RF waveforms are becoming more important in a variety of communication systems. For this reason, a series of non-constant waveforms (BPSK, QPSK, 8PSK, and 12/4 QAM) have been evaluated for use in future satellite systems. Some prior satellite communications systems relied on constant envelope waveforms, such as Gaussian Minimum Shift Keying (GMSK). The solid state power amplifiers (SSPA) for these systems were designed with those waveforms in mind. It is of interest to determine how these amplifiers will perform with the non-constant envelope waveforms in order to evaluate their usable output power capability. A model of a Q-Band SSPA, based on AM-AM and AM-PM measurements, was incorporated in an Agilent Advanced Design System (ADS) Ptolemy simulation. The effects of the power amplifier nonlinearities on error vector magnitude (EVM), spectral re-growth, adjacent channel interference (ACI) and chip error rate (CER) throughput performance were evaluated. Of particular interest was the amount of spectral re-growth and ACI as a function of output power back-off of the SSPA from full power.