Balanced dual-band diplexer design using microstrip and slot-line resonators

A balanced dual-band diplexer formed using hybrid microstrip and slot-line structure is proposed with good common-mode (CM) suppression in this paper. The balanced dual-band diplexer was constructed by combining two dual-band bandpass filters (BPFs) operating at 1.92/5.25 GHz and 2.45/5.8 GHz, respectively, through T-junctions. The incompleteness of the slot-line resonator results from the open-boundary condition along the symmetry plane in CM operation is employed to effectively suppress the CM signals. A prototype of the proposed balanced dual-band diplexer was implemented and measured with a differential-mode isolation of higher than 38.8 (33.4) dB and a CM suppression of larger than 22.9 (22.4) dB in the frequency range of 1-8 GHz.