Abstract
In this paper, coupled split-ring resonators (SRRs) are used to construct the electrically small antennas. We show that through strong magnetic coupling, the coupled SRRs composite can oscillate at a wavelength much larger than its total size. Due to its magnetic dipole feature, the coupled SRRs composite allows the electromagnetic (EM) power to radiate and hence forms the electrically small antenna (ESA). Because of the high-Q resonance, the ESA could be easily matched to the driving circuit in the microwave region, through mutual induction approach. We also demonstrate that the radiation efficiency of such ESAs can be drastically improved if the current distribution on individual SRRs is similar, which is achievable by carefully designing the ESAs. From our simulations and experimental measurements, the ESAs’ radiation efficiency can reach up to 41%, with relative footprint of 0.05λ0 × 0.05λ0. Our approach would be an effective way to realize ESAs with high efficiency, which can be implemented on chip through the standard planar lithography.
Highlights
Nowadays, the electrically small antennas(ESAs) are attracting people’s eyes, due to their reduced size and the capability to be integrated on chip
The basic structure of our ESA is made of an split-ring resonators (SRRs), together with a small feeding loop, as referred to Fig. 1(a)
The SRR with magnetic resonance is placed on the top of the substrate, while the feeding loop is set in the backside
Summary
The electrically small antennas(ESAs) are attracting people’s eyes, due to their reduced size and the capability to be integrated on chip. 7, ESA consists of a monopole and a circular split-ring resonator structure, with footprint 0.095λ0 × 0.1λ0, has a gain up to 2.38 dBi with 43.6% efficiency. 8, the electrically small antenna made of SRR shrinks to a footprint of 0.06λ0 × 0.06λ0, whose gain reaches −1.302 dBi under radiation efficiency 21.4%. The complementary SRR structure shows its ability to further reduce the footprint when applied in designing the ESAs9,10. By using two SRRs with different size, the ESA would be dual banded with a compact structure[14] In this context, we propose the ESA design through multiple coupled SRRs. Our ESA consists of a rectangular feeding loop and several radiating SRRs. To realize strong magnetic coupling, the SRRs are identical, and are aligned and stacked together. The ESAs can have a compact size, and are fabricated through the standard planar techniques
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