Cross-coupled bandpass filters using QMSIW cavities and S-shaped slot coupling structures

This paper presents a novel cross-coupled bandpass filter using quarter-mode substrate integrated waveguide (QMSIW) cavities. QMSIWs with fictitious magnetic walls on two sides retain similar performances of the conventional SIW, but are almost one fourth the size. The dominant resonant mode of the proposed resonator is the TE₁₀₁ mode. A special negative coupling scheme with symmetrical S-shaped slots on the top and bottom metal planes connected by metallic vias is developed. The proposed structure provides more design flexibility in arranging the pitch of vias owing to the extended slot length. The experimental filter has a measured fractional bandwidth of 7.44% at 5.57 GHz with a return loss better than - 18.1 dB and an insertion loss less than - 2 dB.