The AR6A Single-Sideband Microwave Radio System: Predistortion for the Traveling-Wave-Tube Amplifier

Predistortion for the Traveling-Wave-Tube Amplifier By R. P. H E C K E N , * R. C. HEIDT,* and D. E. S A N F O R D * (Manuscript received February 7, 1983) To satisfy the single-sideband amplitude-modulated system noise requirements, t h e t r a n s m i t t e r must be very linear. Predistortion reduces intermodulation distortion of t h e t r a n s m i t t e r to acceptable levels. T h i s paper deals with t h e design considerations, t h e model of t h e t r a n s m i t t e r used to analyze thirdorder intermodulation products, a n d t h e methods applied to align the predist o r t e r - t r a n s m i t t e r combination for effective intermodulation reduction. I. INTRODUCTION T h e frequency stability required for single-sideband amplitudem o d u l a t e d (SSB-AM)1" system o p e r a t i o n results in t h e p o t e n t i a l for in-phase addition of intermodulation noise from repeater to repeater. Traveling-Wave T u b e s ( T W T s ) offer t h e best linearity (and, consequently, t h e lowest intermodulation distortion) available for currently existing 6-GHz power amplifiers. However, linearity must be improved to satisfy system noise requirements. T h e concept of predistortion to reduce intermodulation distortion *Bell Laboratories. + Acronyms and abbreviations used in the text and figures of this paper are defined at the back of this Journal. ®Copyright 1983, American Telephone & Telegraph Company. Photo reproduction for noncommercial use is permitted without payment of royalty provided that each reproduction is done without alteration and that the Journal reference and copyright notice are included on the first page.