Differential Bandpass Filters Based on Dumbbell-Shaped Defected Ground Resonators

This letter presents a dumbbell-shaped defected ground resonator and its application in the design of differential filters. The operation principle of the dumbbell-shaped resonator (DSR) coupled to differential microstrip lines is studied through a circuit model analysis. The proposed circuit model is validated through the comparison with the electromagnetic simulation results. It is shown that the bandpass configuration of microstrip-line-coupled DSR can be used to design higher order bandpass filters. The design procedure is explained by developing a third-order filter prototype. The designed filter shows more than 57-dB common-mode rejection within the differential passband.