Rectangular Waveguide Filters Based on Deformed Dual-Mode Cavity Resonators

In this paper, a novel design for rectangular waveguide filters with deformed dual-mode (DM) cavity resonators is demonstrated. The new resonant cavity shape is a result of applying shape deformation to the basic rectangular cavity to enable its dual-mode operation. Internal coupling between the two orthogonal cavity modes is realized by geometry deformation, eliminating the need for additional coupling elements. The designs are developed within the constraints of 3-D printing to allow their fabrication in one piece. In addition, the design method used results in models with smooth surfaces, which is highly desirable for high-power and low-loss applications. A deformed DM cavity is analyzed and a single cavity second-order filter is designed and presented. Finally, two types of fourth-order filters with transmission zeros are designed by combining two deformed DM cavities and their performance is verified experimentally by a 3D-printed prototype.