A reconfigurable and tunable single to dual wideband bandstop filter by using nested dual-mode square loop resonators

Abstract

This article presents the design of reconfigurable and tunable single and dual wideband bandstop filters. The proposed filters are constructed using two unequal square loop nested dual mode resonators (DMRs) that share one perturbation element on a common edge. The perturbation is used to excite and control the coupling between the degenerate modes of DMR. By varying the size of the perturbation, two reflection zeros (RZs) are shifted from the real to imaginary axis, improving the isolation between the stopbands. The response of the wideband bandstop filter (WBSF) can be converted from a single to a dual band while maintaining the total bandwidth of the filter. Additionally, two reference element pairs are located on the lateral arms of each resonator. Tunability are achieved by controlling the degree of stopbands with both elements and adjusting the upper stopband bandwidth with the inner resonator size, regardless of the total bandwidth. The proposed design is demonstrated with three WBSFs using nested DMRs, and even odd mode analysis of a single DMR is extracted to elucidate topology. The center frequencies for the single and dual band cases are adjusted to 7.26 GHz, 5.13 GHz, and 10.59 GHz. The filters are fabricated and the measured.