Frequency-Reconfigurable Wideband Bandstop Filter Using Varactor-based Dual-Slotted Defected Ground Structure

Abstract

A reconfigurable bandstop microstrip line filter with wide continuously adjustable stopband is proposed in this letter. Dumbbell-shaped defected ground structure cells based on dual coupling slots are used to reduce the complexity of the filter and simplify the equivalent circuit modeling. Three varactors crossing the center coupling slots are utilized together with isolating capacitors to obtain the reconfigurability, of which the frequency range can be adjusted from 1.8 to 8.0 GHz. An equivalent-circuit model using coupled LC resonators is developed to firstly attain physical understanding of the filter’s working principle and secondly to assist the filter design. Three pairs of perpendicular stubs are introduced onto the microstrip line to improve the transmission and maintain signal integrity in the passband. The filter has been fabricated and experimentally characterized, with the good agreement observed between simulation and measurement validating the concept.