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It is demonstrated that the resonant frequency of split ring resonators (SRRs) can be tuned using varactor diodes. The resulting particle, which is called a varactor-loaded split ring resonator (VLSRR), is applied to the design of a tunable notch filter at S-band. The device consists on a microstrip transmission line with VLSRRs placed at both sides of the conductor strip. Owing to the proximity of the particles to the line the rings are excited and a transmission notch arises. It is shown that simply using two VLSRRs pairs, rejection levels above 20 dB are achieved in a 0.5 GHz tuning interval centred at 2.85 GHz. The proposed device is the first tunable notch filter based on SRRs.
Date of Publication: 14 Oct. 2004