Tunable split ring resonators ( SRR ) filter based on barium-strontium-titanate thick film

This paper presents a bandpass filter based on split ring resonators (SRR) with a frequency tunable passband. It consists of two SRRs, which are tuned by the embedded varactors built on Barium-Strontium-Titanate (BST) thick film ceramic. Each SRR embodies a transmission pole and a zero. The resonant frequency of the poles can be shifted by tuning the varactors. The proposed design integrates a novel biasing network for tuning the embedded varactors in the inner and outer SRR rings without any air bridges, vias or discrete decoupling components. The bias lines are made of high resistive electrodes. The achieved passband frequency tuning range is between 2.8 GHz to 3.1 GHz and the insertion loss at the bandpass center is less than 7.5 dB. The size of the planer filter is 14mm×3mm.