Tapering optimization for controlling of intermodulatlon in TWTs

Summary form only given. In many applications TWTs amplifiers are required to provide simultaneous amplification of multiple frequencies. Intermodulation and amplitude and phase cross-modulation effects take place. These effects occur because of the nonlinearities in the amplification process. However, some applications require intermodulation products at levels lower than -60 dBC. In addition, the requirements of further increasing the efficiency, frequency, and power levels of TWTs makes the attainment of these levels of intermodulation challenging. In order to study intermodulation phenomena in the nonlinear regime we are developing time-dependent, multi-frequency models of helix TWTs. In this paper we describe a one-dimensional nonlinear multifrequency model which extends previous work in this field. The extension consists in the ability to treat an arbitrarily large number of distinct signals. It has been suggested that dynamic velocity tapers can, in addition to enhancing the efficiency, extend the range of linearity of the drive curve. In this work, we also suggest the use of tapering in order to reduce the intermodulation products. The results of the optimization of the rates of taper in order to minimize the intermodulation products are presented. These results hold promise that the dynamic velocity taper approach for reduction of intermodulation product can be accomplished more simply than by the conventional feed-forward techniques.