Researches On Metamaterial-based Electrically Small Antennas

With the mobile communication system integration level continuously improve,as one of the important part of it,the higher and higher demands are proposed for antennas.Due to their reduced size and the capability to be integrated on chip,the electrically small antennas(ESAs)are attracting the antenna designers' eyes.The researchers at home and abroad proposed lots of metamaterial-based ESAs in recent years.The advantage of these metamaterial-based ESAs is that they can naturally match with the 50? source without external matching network.And these ESAs' radiation resistance can be improved observably,i.e.a higher radiation efficiency can be realized.This paper mainly studies the working mechanism of the Metamaterial-based ESAs,for the characteristics of very narrow impedance bandwidth and the low radiation efficiency of these ESAs.We put forward effective solutions on expanding ESA's impedance bandwidth and increasing its radiation efficiency.Also,two ESAs were designed,fabricated and tested.The results of numerical evaluation are in good agreement with experimental results,which verifies the correctness of the work in this paper.In this paper,the main works and innovation points are as follows:(1).Summarizing the research status of metamaterial-based ESAs and analyzing the work mechanism of this kind ESAs in detail,as the source of innovation and theoretical basis.(2).A scheme by using multiple split ring resonators(SRRs)to expand ESA's impedance bandwidth is proposed.The innovation point is that by shifting these SRRs to be nonconcentric to decrease the mutual interaction.A broadband ESA can be achieved by simply adding up the three SRRs' respective impedance bandwidth.We use three SRRs to design the ESA,which approximately has three times impedance bandwidth than the single SRRbased ESA.(3).A scheme to improve the ESA's radiation efficiency is proposed.The innovation point is that by stacking the radiators which can realize strong magnetic coupling.Through the strong coupling,the radiators can oscillate at a wavelength much larger than its total size.The current distribution on each radiator is similar,which can improve the radiation efficiency drastically.We use SRRs as the radiators,an ESA working at 1/20 wavelength is designed.The ESAs' radiation efficiency can reach up to 41%.