Novel Compact Substrate Integrated Waveguide Balun Filter and Balanced Filter

In this paper, we present a balun filter and a balanced filter based on substrate integrated waveguide (SIW). By fully utilizing the EM-field properties, only one SIW cavity is needed to realize the presented second-order balun or balanced filter. After properly arranging the locations of input/output ports in a TE102 and TE201 orthogonal modes SIW cavity, the desired 180 degrees phase difference of balun or balanced filter can be obtained. Hence, filtering responses can be easy integrated to the balun or balanced circuits. The design methods of the two circuits are presented. For demonstration, a balanced filter is fabricated and measured. Good agreement between simulated and measured results verifies the proposed ideas.