A Reconfigurable Filter Using Defected Ground Structure for Wideband Common-Mode Suppression

A wideband common-mode (CM) suppression reconfigurable filter is proposed for high-speed all-pass differential circuits. The filter adopts three varactor-loaded compact defected ground structures (DGSs) to achieve continuous reconfigurability in its operation frequency with a large CM suppression dynamic range in the bandwidth. The varactors play an important role in widening the accessible instantaneous bandwidth and miniaturizing the structure. The three DGS cells with a total area of 15 mm × 10 mm are implemented symmetrically under the differential lines, to obtain reconfigurable CM bandstop characteristics which can be continuously adjusted from 1.8 to 8.1 GHz. A coupled LC resonator equivalent model is developed to represent and analyze the proposed filter, which explains its operation principle and assists in accelerating the reconfiguration design method. A good agreement between full-wave simulations and measured results is demonstrated, which validates the proposed design.