Research On Broadband Directional Antenna Based On Metasurface

Metamaterial is a kind of artificial composite materials,which composed of subwavelength unit structures arranged in a specific way.Metasurface(MS)is a two-dimensional ultra-thin plane with periodic arrangement of sub-wavelength unit structures.It can be regarded as a two-dimensional planar metamaterial,which can realize effective controlling of amplitude,phase,polarization,propagation mode and other characteristics of electromagnetic wave.The characteristics of light weight,low profile,low loss and easy realization of the metasurface have been applied in many applications.Meanwhile,it can be combined with the antennas to improve the performances.In this thesis,the reflection characteristics of reflective metasurfaces are studied,and they are utilized as the reflector to design three broadband directional antennas with excellent performance.The main works and contributions of the dissertation are listed as follow:1.Design and research of directional planar spiral antenna based on artificial magnetic conductor.Firstly,the theory of planar spiral antenna is introduced,and an Archimedean spiral antenna(ASA)is designed as a radiating antenna.Then,a miniaturized artificial magnetic conductor unit is designed.The artificial magnetic conductors worked at different frequencies are arrayed in the form of gradient surface and applied to the radiating antenna to obtain a broadband directional antenna.The broadband directional antenna works in the range of 3.3-8.5 GHz with good circularly polarized characteristic within the operating frequency band,and the front-to-back(FBR)ratio is greater than 15 d B.2.Design and research of broadband directional antenna based on single-layer frequency selective surface(FSS).Firstly,a single-layer wide band-stop FSS is designed.Both a circularly polarized ASA and a linearly polarized monopole antenna are used as radiating antennas.The performances of the single-layer FSS in linearly polarized and circularly polarized antennas was analyzed and studied.It is concluded that the FSS will affect the circular polarization characteristics of the ASA in the low frequency band as it is applied to a circularly polarized ASA.On the contrary,the FSS is more suitable for the linearly polarized monopole antenna,which can maintain the impedance bandwidth of the original monopole antenna from 2.29 GHz to 8 GHz.Meanwhile,the backward radiation of omni-directional antenna is reduced,and the gain of the antenna is increased by 4-5 d Bi over the working frequency band.3.Design and research of low radar cross section(RCS)planar spiral antenna based on double-layer frequency selective surface.Firstly,a double-layer FSS,which exhibits a stopband response in the range of 2-4.7 GHz,is designed as reflector of an ASA.Compared with the metal reflector with the same size,the FSS reflector can reduce the RCS of the antenna by about 2.5-38 d B in the frequency range of 4.8-30 GHz,while the circular polarization characteristic is also improved in the frequency range of 2.8-8.1 GHz.