Multiple FM/FDM Carriers Through Nonlinear Amplifiers

For long haul transmissions using frequency-division multiple-access methods, several frequency-modulated carriers are transmitted over a common communications channel consisting of saturating amplifiers operated near saturation to maximize the system power efficiency. One of the problems caused by saturating high power amplifiers is intermodulation distortion, which is the subject of this paper. A simple computation method is introduced which is potentially useful in calculating intermodulation distortion effects of FDM/FM equal power carriers. Based on the results of the study, new and simple empirical expressions for the amplitudes of the single third-order intermodulation products are then presented and compared to previous theoretical and experimental results.