Two miniaturized triple-band filters based on 90⁰ sector substrate integrated waveguide

Two kinds of triple-band filters based on 90⁰ sector substrate integrated waveguide (SSIW) are firstly investigated. The resonant frequencies of SSIW are deduced by analogy with a circular SIW cavity. By contrast, SSIW cavity is not only easier to suppress higher-order modes than the circular SIW cavity, but also easier to cascade multiple cavities. Two kinds of miniaturization filters are realized by using dual-layer and single-layer half-mode structures, respectively. Dual-layer triple-band filter is realized by using TM₁₁₀, TM₁₂₀, and TM₂₁₀. The single-layer triple-band filter based on half-mode SSIW is proposed for further miniaturization. It adopts higher order modes (TM₁₁₀, TM₁₂₀, and TM₃₁₀) to achieve triple-band response. Moreover, it introduces a W-shaped coupling slotline, which not only makes lower original resonant frequencies, but also increases the coupling strengths. Source and load coupling (S-L-C) and CSRR are introduced for improving the selectivity of the proposed two filters. Finally, both filters have been fabricated. The measured results are in line with the simulated ones.