A novel compact dual-band bandstop filter (DBBSF) using spurline & stepped-impedance resonator with a tunable BST capacitors

This paper presents an investigation into a tunable dual-band bandstop filter (DBBSF) using a novel structure compacting a spurline section with a stepped impedance resonator. This new structure creates one new compact filter by combining two traditional controllable methodologies. This compact filter consists of a spurline section and stepped impedance resonator designed at 2 GHz and 3.5 GHz respectively. This filter was loaded with a Ferroelectric capacitor to tune their frequency response. The center frequency of the first band can be tuned from 1.9 GHz to 2 GHz by loading a ferroelectric capacitor to the spurline section and applying a DC control voltage from 0V to 6V. By embedding the stepped impedance resonator with a similar capacitor, the center frequency of the second band can be tuned from 3.2 GHz to 3.6 GHz with the same voltage. The new structure filter will combine a spurline section with a stepped impedance resonator in one filter realizing two independent rejection bands. This kind of filter provides two comparable technologies for dual band filters. It can be used for two different tuned elements with different RF frequencies and bandwidths.