Novel quintuple‐mode broadband microstrip BPF with stub‐loaded multiple‐mode resonator

In this article, a novel compact broadband microstrip bandpass filter with high selectivity and wide upper-stopband performance is proposed using quintuple-mode stub-loaded resonator. The proposed resonator can generate two odd-modes and three even-modes in the desired band. The open stub and short-circuited stub at its central plane can not only specially control the even-mode resonant frequencies, whereas the odd-mode ones are fixed, but also generate two transmission zeros near the upper and lower cut-off frequencies, leading to high rejection skirt. Two identical impedance-stepped open stubs are mainly applied to adjust the high resonant modes (fm4, fm5) into desired passband and excite one additional transmission zero to deepen the upper-stopband. A quintuple-mode broadband filter with the fractional bandwidth better than 64% is simulated, fabricated, and measured. The EM simulated and measured results are presented and excellent agreement is obtained. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:799–803, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25849