Tunable bandstop filters using defected ground structure with active devices

In this paper, tunable bandstop filters using defected ground structure (DGS) sections are presented. The DGS section is obtained by etching the conventional ground plane. To adjust the stopband, voltage controlled variable capacitor diodes (VVC) are equipped on the DGS section. The center frequency of the filter is varied from 1.44 GHz to 3.19 GHz as the reverse bias voltage is changed from 0 V to 20 V. The stopband of the proposed filter has a tunable range of 76%. Using more than two DGS units, deeper suppression and wider tunable bandwidth are yielded. Good agreements between the simulated and measured results are obtained.