One dimensional large signal parametric model of folded waveguide TWTS

We have implemented a simple hybrid circuit model for folded waveguide slow wave structures [1] in the CHRISTINE-CC large signal simulation code [2]. The unit cell of the circuit model consists of an inductive shunt element that represents the interaction gap region, combined with a section of transmission line that represents the folded waveguide. The model has only 4 real valued parameters in the absence of loss, but when the values of these parameters are carefully chosen the model accurately reproduces the dependence of phase velocity and characteristic (Kino) impedance vs. frequency over the operating band as calculated using HFSS. Cold circuit loss is included by introducing attenuation in the waveguide sections and by adding a resistive part to the shunt. By using alternating transmission line lengths, the model correctly reproduces stop bands created at the 3π/2-point when the beam tunnel is offset from its centered position.