Dual-mode filters in equilateral triangular waveguides with wide spurious-free response

Modern satellite communication systems require high performance filters with great compactness and low mass. These features are traditionally offered by dual mode filters. During the last decades, several designs have been implemented using waveguides with different cross-sections such as rectangular, circular or elliptical, where different coupling structures have been proposed. In this paper, a novel implementation using the equilateral triangular waveguide is introduced. One main advantage of this proposed structure is its wide spurious-free window in comparison with other dual-mode implementations. Moreover, the modes of the equilateral triangular waveguide are also analytic, and the full-wave design can be carried out with the efficient Mode-Matching technique. Thus, this type of implementation proves to be as suitable as other structures with analytical waveguides (i.e. the classic rectangular structures), having at the same time a wide spurious-free window response.