Novel hybrid four-mode microstrip bandpass filter using two paralleled stub-loaded resonators

A novel hybrid four-mode microstrip bandpass filter (BPF) is proposed in this paper.The filter is realized by association of two stub-loaded dual-mode resonators. Two similar stub-loaded dual-mode resonators are set in parallel. By appropriately arranging the two dual-mode resonators and the coupling between resonators with the microstrip feed lines, a new hybrid four-mode BPF is achieved. The even- and odd-mode theory is introduced to minutely analyze dual-mode resonators. Moreover the circuit model and coupling matrix of the filter are built to further explain the proposed circuit. The proposed BPF is simulated, fabricated, and measured. Two transmission zeros have been achieved in the transition band of the filter, which improve the performance of the filter. The EM simulated and measured results are presented and excellent agreement is obtained validates the design concept. (c) 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:840845, 2013; View this article online at wileyonlinelibrary.com. DOI: 10.1002/mop.27418