Modified Equivalent-Impedance Approach for Azimuthally Corrugated Lossy Structures

The equivalent-impedance approach (EIA) is applied to calculate the imaginary part of natural frequency of an azimuthally corrugated coaxial lossy cavity in the TE case. Assuming a very small depth and arbitrary shape of corrugation, a simple and efficient formula for the real part of the equivalent impedance of a corrugated surface is obtained. In the case of a small to moderate depth and sectorial shape of corrugation, new modifications of the equivalent impedance where the imaginary part takes into account the dependence on the comb width and modal index are proposed. It is shown that the frequency dependence of the real part of the impedance cannot be neglected even if the groove depth is small. The potentials of the developed approach to analyze and design azimuthally corrugated coaxial lossy cavities are discussed. The limits of validity of the proposed models are estimated by comparing the numerical results of EIA with those obtained in the framework of the rigorous mode-matching technique (MMT).