  Efficient RF power amplifiers used in third generation systems require
linearization in order to reduce adjacent channel inter-modulation distortion,
without sacrificing efficiency. Digital baseband predistortion is a highly
cost-effective way to linearize power amplifiers (PAs). New communications
services have created a 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 (SSAP's) in linearity. This paper presents a technique
for improving TWTA linearity. The use of predistorter (PD) linearization
technique is described 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 Multi-frequency
Minimum Shift Keying (MF-MSK) in non-linear channels are presented in this
paper.
