An inline quarter-mode substrate integrated waveguide (QMSIW) filter with controllable finite transmission zeros (FTZs) is presented based on a novel frequency-dependent coupling structure, which is constructed by a microstrip line with a pair of symmetric metallized via/buried holes and a magnetic coupling iris between two resonant cavities. FTZ can be independently introduced and controlled on both sides of passband to achieve high selectivity while keeping the filter compact configuration unchanged. For demonstration, the proposed structure is analyzed in detail. An inline fourth-order QMSIW bandpass filter (BPF) with two upper FTZs is designed, fabricated, and measured. The synthesis results, EM results, and measured results are in accordance with each other, which confirms the effectiveness of the proposed method.
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