Validity of Surface Impedance Model for Electromagnetic Analysis of a Corrugated Gyrotron Cavity

An approximate surface impedance model (SIM) is widely used in practice to calculate and optimize the electromagnetic properties of corrugated RF structures. According to this model, the corrugated walls are replaced by a homogeneous surface with averaged anisotropic impedance, which depends on the corrugation parameters. In this study, the SIM validity is investigated for TE waves of a circular waveguide with longitudinal wall corrugations. The investigation is based on the full-wave approach, which accounts for the coupling between the fundamental and higher space harmonics. It is shown that this coupling may invalidate the results of the surface impedance model, even though the widely accepted condition of SIM validity is fulfilled.