A Tunable Bandstop Resonator Based on a Compact Slotted Ground Structure

A new slotted ground structure featuring compact size and spurious-free passband in the context of microstrip lines is proposed. The compactness of the new structure originates from the lengthened coupling gap in the ground. The spurious-free response in a wide passband is a result of combining both narrow and wide slots in the new structure, which effectively forms a stepped-impedance slot resonator. Compared to the previously proposed dumbbell- and H-shaped defected ground structure, over 40% size reduction can be realized in the new structure. The new structure also provides flexibilities in introducing additional functionalities to the bandstop resonators. By embedding varactors in the slotted ground structure, tunable bandstop resonators can be implemented and 13% tuning range centered at 2.36 or 2.67 GHz have been obtained.