A Differential Dual-Band Bandpass Filter with Independent CM Response

A dual-band balanced bandpass filter with good common-mode (CM) suppression is proposed in this paper. The proposed filter is composed of two slot-line uniform impendence resonators (UIR) resulting in two differential-mode (DM) bands in 1.5 and 2.5 GHz, respectively. A compact size can be achieved by folding the resonators and embedding one in another. The good CM suppression is obtained by an novel balanced stepped-impendence microstrip-slotline transition structure and the DM characteristics can be adjusted independently from CM response. The simulation results show good DM transmission and CM suppression of this filter.