Novel compact dual-band bandpass filters using composite resonators to obtain separately controllable passbands

In this paper, a novel type of dual-band bandpass filter (DBBPF) is proposed by using composite resonators, and its design method is developed based on the lumped-element equivalent circuit of the filter. Both the midband frequencies and the passband widths of the dual bands of the filter can be controlled separately. Four DBBPFs with different specifications are designed, fabricated and tested, and the measured frequency responses agree favorably with theoretical predictions, validating sufficiently the proposed design theory and filter structures.