Accurate Derivation of Lossy Equivalent Circuit of Waveguide External Coupling

Abstract

A novel technique to derive the lossy equivalent circuit of waveguide external couplings of narrowband cavity filters with arbitrary cavity cross section and arbitrary coupling geometry is presented in this contribution. The technique makes use of a reduced CAD model to obtain the element values of the equivalent lossy circuit. Therefore the contribution of the external coupling structures to the total dissipated power and total stored energy of the filter can be derived and a clear separation between resonators and couplings is established. A first degree filter has been designed, simulated, and manufactured. Its lossy equivalent circuit has been extracted and comparisons with simulation and measurement show excellent agreement.