| The requirements of wireless communication system for antenna performance are increasingly stringent.High gain,low profile,high efficiency and other characteristics have become an important development direction of improving antenna performance.The appearance of artificial electromagnetic surface brings new possibility for the design of antenna.Generally,the artificial electromagnetic surface is composed of unit structure with periodic arrangement.Compared with the traditional materials,the propagation of electromagnetic wave in the artificial electromagnetic materials will show different characteristics.These characteristics fundamentally change the propagation mode of electromagnetic wave.It can be more flexible to adjust and control the electromagnetic wave.Therefore,domestic and foreign researchers have made great efforts to study different applications of artificial electromagnetic surface in the design of antennas.In this dissertation,the application of artificial electromagnetic surface in antenna is studied deeply,and the reconfigurable method of antenna using artificial electromagnetic surface is designed and improved.The main research contents are given as follows:1.The theoretical analysis method and simulation modeling method of artificial electromagnetic surface are studied in this dissertation.The goal of this dissertation is to improve the control ability of artificial electromagnetic surface in controlling surface wave and space wave.Firstly,two main analysis methods of artificial electromagnetic surface are discussed in detail.They are transverse resonance analysis method for surface wave propagation and generalized Snell’s law analysis method for space wave propagation.The transverse resonance analysis method mainly studies the impedance modulation characteristics of the artificial electromagnetic surface for the surface wave propagation,and the generalized Snell law analysis method mainly studies the phase modulation characteristics of the artificial electromagnetic surface for the space wave propagation.On the basis of principle analysis,the simulation modeling methods based on two analysis methods are further studied,which lays a theoretical foundation for the research work.2.One-dimensional impedance modulation characteristics of artificial electromagnetic surface are studied in this dissertation.Impedance modulation surface is one of the important applications of artificial electromagnetic surface.This dissertation takes the design of plane leaky-wave antenna as an example to elaborate the design method of one-dimensional impedance modulation surface.The leaky-wave antenna has the characteristics of frequency sweep,that is,the beam angle of the leaky-wave antenna only changes with frequency.Thus,it is difficult to realize beam angle scanning at a fixed frequency by conventional design method.To solve this problem,a plane leaky-wave antenna with fixed-frequency beam reconfiguration is designed in this dissertation.Varactor diodes are added into the one-dimensional impedance modulation surface.By independent control of varactor diodes,the modulation surface impedance and modulation period can be adjusted simultaneously.Compared with the existing research results,the antenna proposed in this dissertation can obtain a larger angle scanning range.The experimental results show that the proposed antenna can achieve a beam scanning range of 118° at 8 GHz.At the same time,due to the highly reconfigurable characteristics of the proposed modulation surface,the beam number of the proposed antenna can also be controlled.The proposed antenna can work in single-beam radiation mode and dual-beam radiation mode,and independently control of the angle of each beam is achieved.3.Two-dimensional impedance modulation characteristics of artificial electromagnetic surface are studied in this dissertation.Based on the design of one-dimensionalk impedance modulation surface,in order to further improve the ability of artificial electromagnetic surface to control surface wave,this dissertation takes the design of planar holographic antenna as an example,and expounds the design method of two-dimensional impedance modulation surface in detail.Holographic antenna is a kind of leaky-wave antenna,and its design method is the combination of impedance modulation leaky-wave theory and microwave holographic theory.In this dissertation,a beam reconfigurable holographic antenna at a fixed frequency is proposed.The antenna consists of two-dimensional impedance modulation surface and feed control circuit.For the design of modulation surface,this dissertation innovatively proposes an improved method of impedance modulation.The whole modulation surface is divided into four parts and the impedance information of two beams is mudolated in each part.Thus,the whole modulation surface can contain the impedance information of four beams.The whole modulation surface is composed of 5329 unit cells.The antenna beam can be switched between four radiation states by exciting different monopole sources through the feed control circuit.The experimental results show that four switching beams are achieved at 18 GHz,and all of the four beams have good directivity with gain greater than 17 d Bi.4.Phase modulation characteristics of artificial electromagnetic surface are studied in this dissertation.The modulation effect of artificial electromagnetic surface on electromagnetic waves is not only limited to surface wave.A lot of research has been done on the space wave modulation of artificial electromagnetic surface.In recent years,vortex wave with orbital angular momentum(OAM)has attracted the attention of researchers for its significant role in improving channel capacity.As one of the applications of artificial electromagnetic surface,phase modulation surface plays an important role in the design of OAM antenna.Taking the design of OAM antenna as an example,this dissertation studies the modulation effect of phase surface on space wave,and a single-layer transmission OAM antenna at 18 GHz is designed and fabricatead.The proposed design is based on the improved unit cell.By adding metal via structure,the capacitance effect between metal strips on the upper and lower surfaces of the dielectric is suppressed.Ttransmission loss of the unit cell is greatly reduced.Meanwhile,current path is extended by the metal via structure and the phase adjustment range of the unit cell is increased.Compared with the existing research results,the OAM antenna proposed in this dissertation has the advantage of low profile.The experimental results show that the proposed design can effectively generate OAM vortex wave.At the same time,a single-layer reflection OAM antenna operating at 5.5GHz is presented in this dissertation.Furthermore,a reconfigurable method of the proposed reflection OAM antenna is studied and designed,which can achieve reconfigurable OAM mode with one antenna. |
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