Compact dual-band bandpass filter and diplexer using hybrid resonant structure with independently controllable dual passbands

In this article, a compact dual-band bandpass filter (BPF) is developed using a hybrid resonant structure, which consists of a microstrip stub-loaded dual-mode resonator and a slotline stub-loaded dual-mode resonator. These two resonators, both having two controllable resonant modes and one transmission zero (TZ), are analyzed and used to construct two desired passbands of a dual-band BPF. Multiple TZs are generated by introducing a source-load coupling, thus improving the selectivity of the passbands. Then, the dual-band BPF is reshaped to configure a compact diplexer. The inherent TZs of the two proposed resonators are designed to improve the frequency property and port isolation of the diplexer. Finally, a dual-band BPF and a diplexer with the lower and upper passbands centered at 2.45 and 3.45GHz, respectively, are designed, fabricated, and measured to verify the proposed structure and method.