Multifunctional reconfigurable microstrip filter based on stub loading

As the communication spectrum becomes increasingly complex, reconfigurable filters that integrate multiple operational bands have garnered significant interest. This study proposes two reconfigurable filters, each operating in four and two distinct modes, respectively. Filter A is designed using the short-circuit stub-loaded resonator (SCSLR) and operates within the 0–4 GHz range. By loading short-circuit stubs at the ends of the resonators, four operational modes are achieved through the control of PIN diodes: dual-passband, high-passband, low-passband, and zero-passband. All modes exhibit high-rejection attenuation exceeding 40 dB, with an average roll-off rate of 141.1 dB/GHz in the transition band. Filter B utilizes transverse signal interaction and incorporates open stubs into the source-load structure. This design operates within the 0–10 GHz range and achieves two states: a dual-mode passband, a quad-mode passband, and an additional dual-mode passband. Compared to Filter A, Filter B offers a larger fractional bandwidth, more resonant modes, and a more compact overall size. Both reconfigurable filters exhibit high passband selectivity and achieve mode switching with a relatively small number of PIN diodes.