Measurement, modelling, and simulation of drift space leakage signals in crossed-field amplifiers

Abstract

Summary form only given, as follows. Previous experimental results have indicated an RF signal leakage through the drift space of Crossed-Field Amplifiers (CFAs). We have collected frequency swept S-parameter data for both CFA on and off conditions and transformed these results to the time domain. Two time signals in addition to the main path signal have been found in S/sub 21/(t) data, which originate from drift space leakage. One of the additional time signals precedes the main path signal and the other is delayed with respect to the main path signal. The preceding time signal is due to a quick passage path from input to output, without ever entering the main path slow-wave circuit. The delayed time signal originates from a signal which travels along the slow-wave circuit, passes through the drift space, and travels along the slow-wave circuit a second time before exiting the CFA as output. We have confirmed the presence of three time signals in CFA off response by conducting real-time digitization experiments. A model has been developed to describe leakage and main path signals, as well as a method of determining model parameters from S-parameter values. The inclusion of RF drift space leakage in the MASK simulation program is achieved by introducing a feedback impedance, with an impedance value determined using measured S-parameter results and MASK slow-wave circuit model parameters. The importance of RF drift space leakage on amplifier performance characteristics such as signal to noise ratio are emphasized.