TWT performance enhancement using higher-order predistortion linearization techniques

Predistortion linearization is a very effective technique for improving the linearity and efficiency of traveling-wave tube (TWT) amplifiers. In this report, we will study the effectiveness of predistortion techniques for TWT linearization using single-tone, two-tone, and quadrature-amplitude-modulation (QAM) signals. The results from a series of predistortion linearization experiments for 5 TWTs covering L-, C-, Ku- and Ka-bands and including both helix and coupled-cavity TWTs will be presented. We will demonstrate the additional improvement of fifth-order predistortion linearization over the more commonly used third-order predistortion linearization. To circumvent the complexity and limited availability of a pure fifth-order linearizer, a technique for realizing nonlinear functions of order greater than or equal to five using cascaded third-order nonlinear functions is described. The technique can be used to efficiently generate higher-order nonlinearities for predistortion linearization applications. We will demonstrate experimentally that the use of two cascaded third-order functions is comparable to a pure fifth-order implementation in performance.