Compact and High-Selectivity SIW Multi-Channel Diplexers and Dual-Band Filters Based on the Lowest-Order Dual-Mode Box-Like Topology

This paper proposes a class of compact, sharp roll-off, and substrate-integrated-waveguide (SIW) multi-channel diplexers and dual-band filters based on the lowest-order dual-mode (DM) box-like topology. To extend the spurious-free bandwidth, the DM box-like coupling scheme was thoroughly examined to relate various frequency responses to each individual set of conditions for coupling matrix elements, by which two lowest-order modes are readily applied to all realizations. Furthermore, a novel control technique by use of the characteristic of the higher/lower-order modal cross coupling in SIW cavities is proposed to independently control each pair of transmission zeros above and below the passband. It is seen that, for proposed quad-channel diplexer, up to eight transmission zeros are highly controllable. As a proof-of-concept, the millimeter-wave four-pole SIW quad-channel diplexer, diplexer, and a dual-band filter were prototyped to achieve compactness, sharp roll-off skirt or/and high isolation.