Reconfigurable CPW Band-Stop Filter Based on Loaded T-Shaped Defected Ground Structure

This paper presents the design and implementation of a reconfigurable band-stop filter based on a coplanar waveguide (CPW) transmission line incorporating defected ground structures (DGS). The proposed filter consists of two pairs of T-shaped resonators loaded with varactor diodes and embedded in the ground plane of the CPW. The biasing configuration in the pair of resonators, either symmetric or asymmetric, enables dynamic tuning of the stopband frequency and bandwidth. The filter also features switchable functionality when the resonators are deactivated via forward-biased diodes, the structure behaves as an all-pass filter, exhibiting insertion loss below 1 dB over the 525 MHz to 3.255 GHz range. A parametric study investigates the influence of the spacing between resonators on the filter’s response to account for the mode splitting effect. Full-wave simulations and experimental results demonstrate tunable stopbands with isolation levels better than 20 dB from 1.40 to 1.65 GHz, with bandwidths ranging from 50 to 175 MHz. The proposed filter exhibits sharp roll-off characteristics, effective tuning and multifunction behavior, large isolation in the stopband and low insertion loss in the passband, making it a strong candidate for integration in adaptive RF front-ends, cognitive radio systems, and frequency-agile microwave circuits.