High power amplifiers (HPA) in microwave range suffer from the effects of amplitude modulation to amplitude modulation distortion (AM/AM), and amplitude modulation

250 Abstract—Trellis coding combined with expanded signal sets has been considered in this paper to improve error performance over uncoded modulation. New communications services have created the demand for highly linear high power amplifiers (HPA's). Traveling Wave Tubes Amplifiers (TWTA) continue to offer the best microwave HPA performance in terms of power efficiency, size and cost, but lag behind Solid State Power Amplifiers (SSPA's) in linearity. This paper presents a technique for improving TWTA linearity. The use of pre-distorter (PD) linearization technique is found to provide TWTA performance comparable or superior to conventional SSPA's. The characteristics of the PD scheme is derived based on the extension of Saleh's model for HPA. The analysis results of hybrid modulation scheme derived from combination of frequency and phase shift keying (FSK/PSK) or (FPM) in non-linear channels are presented in this paper.