A balanced dual-band BPF with quasi-independently tunable center frequency and bandwidth

By introducing an open stub loaded resonator (OSLR) and a uniform impedance resonator (UIR) into balanced stepped-impedance microstrip-slotline transition structures, a balanced dual-band bandpass filter (BPF) with high selectivity and low insertion loss performance is presented in this paper. The balanced microstrip-slotline transition structures can achieve a wideband common-mode (CM) suppression. Meanwhile, the differential-mode (DM) passbands are independent from the CM responses, which greatly simplifies the design procedure. In addition, four varactors are loaded into OSLR and UIR to achieve the electrical reconfiguration. The proposed balanced dual-band BPF can realize quasi-independently tunable center frequencies and bandwidths. In order to verify the feasibility of the proposed design method, a prototype circuit of the proposed reconfigurable balanced dual-band BPF is simulated, fabricated and measured. A good agreement between the simulation and measurement results is observed.