Calculation and measurement of intermodulation products in TWTs

Summary form only given. Dependable tools for physically modeling the effects of multiple tones in traveling-wave tubes (TWT) are required in order to modify TWT designs to increase linearity and reduce the significance of intermodulation distortion (IMD). Ideally, the calculation tools are capable of running in short time intervals on desktop workstations. We will present the results of a study aimed at predicting the performance of a tube under development at Hughes Electron Dynamics Division (HEDD). The analysis consists of two distinct parts. In the first part, we use Qhelix, a proprietary TWT design code developed at HEDD which predicts IMD by post-processing the TWT amplitude and phase transfer curves using a fast Fourier transform (FFT) method. In the second part of this study, we model the TWT with Christine, a true multi-tone TWT code developed by researchers at the Naval Research Laboratory (NRL), that tracks the interaction of multiple RF signals with the electron beam in the TWT structure.