Low Profile Metamaterial Band-Pass Filter Loaded with 4-Turn Complementary Spiral Resonator for WPT Applications

In this paper, a very compact $(0.03\lambda_{\mathrm{g}}\times 0.18\lambda_{\mathrm{g}})$ and low insertion loss (<0.4 dB) metamaterial band-pass filter (MBPF) at the center frequency of f0=730 MHz is proposed, based on the rectangular-shape 4-turn complementary spiral resonators (4-CSR). The proposed MBPF consists of an interdigital capacitor as a series capacitance in the top layer, leading to improve the stopband performance in the pass-band range of 700~760 MHz, which makes it suitable for wireless power transfer (WPT) systems by rejecting unwanted signals. In order to validate the performance of the proposed technique, the MBPF is fabricated on the RO-4003 substrate and great agreement is achieved between simulated and measured results. The stop-band attenuations of greater than 52 dB and 20 dB are obtained around the 0.8×fcl(lower cutoff frequency) and 1.2×fcu(upper cutoff frequency), respectively.