A novel spiral defected ground structure and its application to the design of dual bandstop filter

In this paper, a new type of dumbbell-shaped defected ground structure (DGS) called spiral DGS is introduced, which adopts spiral capacitance instead of direct slot capacitance. When compared with direct slot capacitance, spiral capacitance can improve coupling of capacitance, thus lower resonant frequency is obtained for the same circuit size. Simulated results show that a 3.57 GHz lower resonance is achieved, which is useful for the design of miniature devices. Based on the proposed DGS and spiral split ring resonators (SSRR), a compact dual stopband filter (DBSF) is designed and fabricated in this paper. Its dual-bandgap characteristics are verified by both simulation and measurement.