A Tunable Notch Resonator Based on Varactor-Loaded Complementary Split-Ring Resonators

摘要

Since Pendry pioneered experimental works on the split-ring resonator (SRR), this structure has been applied to a variety of microwave device designs requiring an artificial media with negative permeability [1]. When time-varying magnetic field penetrates a SRR in the particular direction, this SRR structure has high negative/positive permeability values above/below the resonant frequency, and this leads to inhibition of wave propagation in vicinity of that frequency. In the vicinity of the resonant frequency, the SRR shows sub-wavelength property with electrically very small size, which is greatly adequate to miniaturization of microwave devices. This is a promising method compared to traditional ways from the size-reduction point of view. Recently, the feasibility of size reduction for a planar bandstop filter using SRRs has been demonstrated [2]. In addition, a compact notch filter using complementary SRRs (CSRRs) was developed based on the duality concept (Babinet principle) [3]. These structures have shown more compactness than early stage of EBG structures for planar filter applications. Thereafter, a varactor-loaded SRR (VLSRR) for tunable notch filters has been proposed by Gil et al. [4]. Furthermore, a tunable metamaterial transmission line was developed using VLSRRs and metallic vias emulating shunt inductances [5]. This electronic control for metamaterials was applied to microstrip leaky-wave antennas [6], [7]. In this paper, a tunable notch resonator based on CSRRs using varactor is proposed. This new resonator, called by the authors as varactor-loaded complementary SRRs (VLCSRRs), is a promising component thanks to its compact and tunable characteristic as VLSRRs.