A Novel Class of Compact Dual-Mode Rectangular Waveguide Filters Using Square Ridge Resonators

A novel dual-mode resonator for the design of compact waveguide filters is proposed in this paper. The resonator consists of a nearly-square ridge realized into a rectangular waveguide that supports the fundamental TE₁₀ mode. With this configuration two degenerate modes can resonate along orthogonal directions within the gap between the ridge and the opposite waveguide wall. By combining multiple ridges, higher order filters with pseudo-elliptic response can be realized within compact waveguide sections. A 4^th order filter with two transmission zeros has been designed, manufactured and tested proving the feasibility of the proposed class of filters.