COMPACT FREQUENCY AND BANDWIDTH TUNABLE STOPBAND FILTERS USING SPLIT RING RESONATORS AND VARACTORS COUPLED TRANSMISSION LINE
Cheolbok Kim, Xiaoyu Cheng, David Senior and Yong-Kyu Yoon
Two highly compact tunable stopband filters using microstrip transmission lines coupled with split ring resonators (SRRs) and varactor diodes are presented. Frequency or bandwidth tuning capability of each device is demonstrated. The frequency tunable filter, realized by a single stage, shows a wide tuning range of 19.8% with a maximum bandwidth of 5% and an insertion loss of approximately 20 dB at 4 GHz. The bandwidth tunable filter, realized by double stages, shows a 10-dB bandwidth of 19?34% with a biasing voltage of 0?10 V. The implemented frequency tuning and bandwidth tuning devices show a significant area reduction of 60.1% and 53.5%, respectively, in comparison with a similar frequency or bandwidth tunable structure presented by others. Equivalent circuit models are presented. The measured S-parameters are in good agreement with simulated ones.
Keywords: Split ring resonator (SRR), Metamaterial, Varactor, Tunable filter and Wide bandwidth