Compact fully-canonical dual-band bandpass filter with independently controllable bandwidths

A compact four-order fully-canonical dual-band bandpass filter (DBBPF) with independently controllable bandwidths is reported in this letter. The filter comprises of a pair of identical electrically end-coupled dual-mode open stub-loaded resonators (OSLRs) and two different pairs of magnetically coupled lambda/4 short-circuit resonators (SCRs) that are embedded within the OSLRs for compactness. Specifically, the fundamental odd- and even-mode of the OSLRs are coupled with the upper and lower pairs of lambda/4 SCRs to generate the first and second passbands, respectively. In addition, the input and output ports feed the two OSLRs and provide a magnetic source-load coupling for the filter. Owing to the special layout arrangement, the proposed filter can achieve compact size and fully-canonical frequency response with independently controllable bandwidths, simultaneously. A four-pole DBBPF protype centred at 2 and 3.5 GHz is designed and implemented. The measurements and the simulated ones are in good consistency.