LINC transmission using traveling wave tubes

Abstract

Summary form only given. The nonlinear characteristics of traveling wave tube (TWT) amplifiers are often described by AM/AM and AM/PM curves which relate the change in output amplitude and phase to the change in input amplitude. It is desirable to operate the TWT well into the nonlinear regime (i.e., near saturation) to maximize power efficiency. However, nonlinear operation causes out of band emission, resulting in interference for other users, and in band signal distortion resulting in reduced data transmission rates. A variety of linearization techniques have been proposed to reduce these distortions. In this poster we investigate application of the linear amplification using nonlinear components (LINC) method to TWTs. The LINC scheme has been studied in the context of solid state power amplifiers, but does not appear to have been considered for use with TWTs. The LINC method requires a signal component separator that generates two baseband constant envelope signals from the baseband input signal, two quadrature modulators for up conversion of the baseband constant envelope signals, and two matching amplifiers followed by a power combiner. Under ideal conditions LINC results in no nonlinear distortion since the amplifiers operate at a fixed point on the AM/AM and AM/PM curves. However, in practice impairments result from nonidealities in the signal component separator, quadrature modulators, and mismatch between the amplifiers. We examine the effects of amplifier mismatch and device imperfections in order to determine the suitability of a TWT based LINC scheme for common modulation methods.