A time-domain circuit simulator for coupled-cavity traveling-wave tubes

The Curnow equivalent circuit was used to predict the dispersion of cold coupled-cavity traveling-wave tubes, as wen as the voltage and current characteristics for lossless and lossy multicavity circuits. The equivalent circuit is extended to have three ports. The added beam port allows the future modeling of the interaction between beam and cavity. Losses are introduced into the circuit as resistors in series with the corresponding inductors. The time-domain solution to the multicavity circuit is developed. It can be applied to the full-spectrum signal. It is also useful for the transient analysis for both single frequency and full-spectrum signals, including the turn-on transients. Numerical methods to solve the time-domain equations are discussed; a second-order leap-frog method and a fourth-order Runge-Kutta method are implemented and analyzed. Simulation results from both codes are compared, and match well with the theory.