Compact dual‐band bandpass filter with flexible passband frequencies and sharp skirt using cross coupling and mixed magnetic and electric coupling.

This paper presents the design of a compact dual‐band bandpass filter (DB‐BPF) with flexible passband frequencies and sharp skirt. A pair of stub loaded stepped‐impedance resonators (SL‐SIRs) together with two different tri‐section stepped‐impedance resonators (TS‐SIRs) constitute this DB‐BPF. The low impedance sections of two SL‐SIRs and one TS‐SIR are realized by ring structure, on the one hand to acquire two independent resonant modes of SL‐SIRs, and on the other hand to let the harmonic mode of TS‐SIR be away from the upper passband. The cross coupling, the canceling effect of mixed electric and magnetic coupling (MEMC), and the virtual ground introduce the TZs, resulting in the sharp skirt property of proposed DB‐BPF. Step‐to‐step design process is given to guide the DB‐BPF design. As an example, a 0.9 / 1.8 GHz DB‐BPF is designed and fabricated. The fabricated sharp skirts DB‐BPF has a compact size of 0.079λg × 0.193λg, low passband loss of 0.84 / 0.98 dB and high band‐to‐band rejection of better than 40.6 dB. [ABSTRACT FROM AUTHOR]