Comparison of transfer curve induced distortions to distortions in nonlinear physical TWT models

Abstract

Summary form only given, as follows. AM/AM and AM/PM curves are widely used to describe the non-linear behavior of Traveling Wave Tubes (TWTs). Several authors have studied these curves with large signal codes. It has been stated that the phase nonlinearity is related to the slowing down of electrons and the phasing of the charge density with respect to the circuit voltage. Furthermore, in the case of multifrequency inputs, for drive levels restricted to the linear portion of the AM/AM curve, intermodulation distortions are predicted by the phase nonlinearity. In this case again the phase of the charge density with respect to the circuit voltage is shown to be important. However, a direct connection between the distortions generated by the transfer curves and the physical models has not been made. For example, neither the AM/AM nor the AM/PM curves produce distortions about the harmonics of the carrier frequency, which are widely known to exist. Recently we have developed an approximate nonlinear physical model of the TWT, valid prior to saturation, that is analytically solvable. We compare the analytic solution of the AM/PM curve and its role in intermodulation generation to the direct analytic prediction of intermodulation distortions afforded by the solutions to the physical model.