High Common-Mode Rejection Wideband Balanced Bandpass Filter Based on Dual-Mode Semicircular Patch Resonator and DGSs

A novel method used to design wideband balanced bandpass filter (BPF) is validated through a dual-mode balanced BPF based on semicircular patch resonator. In order to arrange the differential-mode (DM) passband, TM 11 and TM31 modes are adopted. Approaches are employed to amend the disparity of the modes' resonant frequencies. For instance, two rows of vias are introduced to perturbed the electric field distribution of TM 11 mode, which can shift the resonant frequency of TM 11 mode to that of TM31 mode; two small patches are located at the balanced ports to decrease the resonant frequencies of TM 11 and TM31 mode. Subsequently, for the purpose of common-mode (CM) suppression, cascaded defected ground structures (DGSs) are etched in the ground plane under the differential transmission line. The wideband balanced BPF is fabricated and measured. The results agree with each other very well, which validate the feasibility of the proposed design concept.