Multimode Bandpass Filter Based on Single‐Layer Substrate Integrated Waveguide

ABSTRACT This paper presents a novel quad‐mode single‐layer cavity substrate integrated waveguide (SIW) bandpass filter designed for millimeter‐wave communication systems. By analyzing the electric field distributions of the first six resonant modes in a rectangular SIW cavity, four higher‐order modes—TE 103 , TE 201 , TE 104 , and TE 202 —are selected to construct the passband. To bring the resonant frequencies of these modes closer, vias are introduced at the vertical centerline of the cavity, along with symmetrically placed slots around them to enhance intermodal coupling. Based on this coupling mechanism, a fourth‐order SIW filter is designed and implemented, exhibiting excellent selectivity and multiple transmission zeros (TZs). Measured results show that the filter achieves a sharp roll‐off and good out‐of‐band rejection at a center frequency of 33.4 GHz. With its compact structure, high selectivity, and multiple TZs, the proposed filter is well‐suited for integrated applications in millimeter‐wave receiver front ends.