Coupled-Mode Theory of an Irregular Waveguide with Impedance Walls

The eigenvalue problem is solved for a longitudinally inhomogeneous waveguide with impedance walls. The cross-section method is applied to reduce the problem to an infinite set of ordinary differential equations for amplitudes of basis modes. As a numerical example, a tapered metallic cavity of currently available THz gyrotron is considered. The combined effect of mode coupling (conversion) and ohmic wall losses on electromagnetic properties of the gyrotron cavity is considered and discussed .