Binary Bandwidth-Reconfigurable Bandstop Filters

This study proposes binary bandwidth-reconfigurable bandstop filters (BSFs) capable of achieving$2^{M}$discrete bandwidth states with only$M$control voltages, implemented in both lumped-element and distributed-element circuit topologies. In the lumped-element binary bandwidth-reconfigurable BSF, each reconfigurable resonator consists of$M$parallel-connected series$LC$resonators—each tuned to the same frequency and selectable via p-i-n switches. For the distributed-element binary bandwidth-reconfigurable BSF, inspired by the conventional open-stub BSF structure, each stub is substituted by a set of switchable open stubs, all connected to the main transmission line (MTL) through p-i-n diodes. The set of switchable open stub designs behaves as a quarter-wavelength stub with a binary-reconfigurable characteristic impedance, enabling$2^{M}$distinct bandwidth configurations. To verify the proposed concept, two prototype 3-bit binary bandwidth-reconfigurable BSFs were designed and fabricated: one lumped-element filter operating at 285 MHz, and one distributed-element filter at 2 GHz. The achievable bandwidths can be digitally reconfigured from 10 to 70 MHz and from 0.62 to 1.74 GHz, respectively. These results demonstrate precise digital control and highlight the versatility and compactness of the proposed architectures for BSF design in frequencies ranging from below ultra-high frequency (UHF) to above L-band.