Compact balanced filters with enhanced differential-mode out-of-band response using coupled slotline structure

Two compact balanced filters using coupled slotline structure are presented in this paper with intrinsic common-mode (CM) rejection and enhanced differential-mode (DM) out-of-band response. By properly designing the proposed U2 folded stepped-impedance slotline resonators (SISRs), compact size and extended DM upper-stopband rejection could be achieved. Specifically, two balanced filters with second-order and third-order coupled slotline resonators (SRs) are implemented. Measured and simulated results are in approximate agreement with each other, showing inherent CM rejection and enhanced DM out-of-band performance such as improved selectivity, multiple transmission zeros (TZs) as well as extended upper stopband.