Aperture-Coupling Effect of Two-Layered Open-Loop Microstrip Bandpass Filters Designed by the Cul-de-Sac Coupling Matrix

Planar-circuit filters based on the Cul-de-Sac coupling matrix is proposed by using square and hexagonal open-loop microstrip resonators. The resonators are arranged to be strongly coupled to the adjacent resonators. The filter is constituted by the two dielectric layers having a coupling apertures. Effectiveness of the proposed filter is investigated numerically and experimentally.