Field-theory analysis of cross-iris coupling in circular waveguide resonators

Dual-mode circular waveguide filters employ cross-iris couplings usually designed by small-aperture approximations. This Letter presents a full-wave method, which is able to rigorously analyze irises of any shape, thickness, and size, based on a mixed finite-element method (FEM) and a mode-matching technique. The accuracy of the method has been tested by comparing measured and computed data.