| Vortex electromagnetic wave is a kind of beam with special spatial distribution of spiral phase wave front with orbital angular momentum(OAM).Because different topological loads correspond to different orbital angular momentum,vortex electromagnetic wave has different phase wave front,amplitude and polarization spatial distribution.Compared with the traditional frequency modulation,intensity modulation and polarization modulation technology,vortex electromagnetic wave can make full use of orbital angular momentum for information modulation and reuse,and can effectively increase the data transmission rate and density.The vortex electromagnetic waves distributed in different directions and spiral polarization spaces,especially the angular momentum of different orbitals,are orthogonal to each other,which increases the degree of freedom of information modulation.More angular phase information can be obtained from reflected wave signals in target detection and imaging applications,which points out the direction for the research and development of new radar.In recent years,metamaterials have become a new research focus in optics,electromagnetics,informatics,material science and other interdisciplinary disciplines.As a two-dimensional manifestation of metamaterials,hypersurfaces have attracted extensive attention because of their high flexibility,low profile,easy processing and so on.In this paper,we use artificial electromagnetic materials(two-dimensional electromagnetic hypersurface)to realize the regulation of electromagnetic wave,produce dual-frequency double-line polarization double-mode,line circular polarization adjustable,multi-beam multi-modal,double-line polarization double-mode diffraction characteristic vortex electromagnetic wave,and use surface wave modulation method to produce high-order Bessel vortex electromagnetic wave without diffraction characteristics.Using the surface wave modulation mechanism anisotropic holographic impedance surface to realize the line,circular polarization mixed mode vortex electromagnetic wave near field detection.The near-field scattering of a simple conductor target is theoretically calculated and experimentally analyzed.Results have been achieved mainly in the following areas: 1.By using the method of polarization incident wave generation by reflection array modulation line and variable circular polarization,a multi-resonant cross orthogonal distribution double-layer patch reflection array element is designed.The influence of the size change of one polarization direction element on the phase compensation realized by the other orthogonal polarization direction is analyzed.The generation of vortex electromagnetic wave with circular polarization can be realized flexibly by using different incident polarization angles of linear polarization incident wave.2.Based on the coupling suppression technique between dual-band resonant elements with orthogonal polarization distribution,aiming at the inherent narrow band defect of vortex electromagnetic wave produced by microstrip array antenna,a reflection array antenna with dual polarization,dual frequency band and double beam carrying angular momentum vortex electromagnetic wave in different orbit is proposed and designed.The radiation and transmission characteristics of two single-band reflection arrays and two-band reflection arrays are analyzed by full-wave simulation and experimental measurement.It is proved that the orthogonal interval arrangement of the two groups of multipoles can effectively suppress the coupling effect between the two frequency segments and improve the bandwidth of vortex electromagnetic waves produced by the reflection array.3.The basic theory of anisotropic holographic metasurface modulation surface wave is studied.Based on the concept of optical holographic and the principle of microwave leakage wave,the anisotropic holographic impedance hypersurface is innovatively introduced into the generation of vortex electromagnetic wave.A new mechanism method of generating vortex electromagnetic wave on the surface of anisotropic holographic impedance is first proposed.An antenna with OAM mode value of 1 working at 20 GHz prototype is designed and fabricated.The near field radiation performance of the vortex wave antenna is measured,which is in good agreement with the simulation results.The generation of other high order topological charge OAM is also studied,which effectively solves the problem of high profile under spatial wave modulation mechanism,and lays a foundation for the integration of vortex electromagnetic wave antenna based on artificial electromagnetic surface with other systems.4.It is proposed that several different spatial radiation directions carry different modes of OAM vortex electromagnetic waves as object waves.Through the idea that multimodal vortex electromagnetic wave can be generated by a single holographic impedance surface array modulation,a vortex electromagnetic wave antenna with orthogonal bilinear polarization carrying different orbital angular momentum in the same radiation direction is designed and developed.the OAM mode value is 1 in the x axis polarization direction and-1 in the y axis polarization direction.The measured results are in good agreement with the simulation results.The flexibility and wave field regulation of multimode and double polarization modulation on anisotropic holographic metasurface lay a foundation for multimode OAM vortex electromagnetic wave multiplex communication.5.A method of generating high-order Bessel vortex electromagnetic waves on the surface of anisotropic holographic impedance based on surface wave modulation is proposed.A positive first-order Bessel vortex electromagnetic wave array antenna is designed and developed.the transmission characteristics of high-order Bessel vortex electromagnetic wave antenna are measured and simulated.It is proved that the high-order Bessel vortex electromagnetic wave without diffraction characteristics can be produced on the metasurface of anisotropic holographic impedance.The vortex electromagnetic wave array antenna can not only solve the problem of high spatial wave profile of space-fed metasurface modulation based on axial cone prism principle,but also flexibly control the polarization mode of high-order Bessel vortex electromagnetic wave,which lays a solid foundation for the application of high-order Bessel vortex electromagnetic wave.6.Based on the lower line of surface wave modulation,the angular momentum mode detection and separation of circularly polarized hybrid orbit are studied.In this paper,the detection method of vortex electromagnetic wave at present is discussed,and the receiving mode and applicable range of angular momentum in single mode and two mode orbit are introduced.The line and circular polarization mixed mode OAM vortex electromagnetic wave anisotropy holographic impedance surface antenna is designed and fabricated.The detection method of vortex electromagnetic wave is studied.The variation of transmission coefficient of mixed orbit angular momentum mode vortex electromagnetic wave produced by space-fed array metasurface based on space wave modulation is analyzed in a certain working frequency range.The experimental results show that the detection and separation of angular momentum mode of anisotropic holographic impedance hypersurface and circularly polarized mixed orbit based on surface wave modulation mechanism.7.On the basis of the incident field of higher order Bessel vortex electromagnetic wave,the internal field of uniaxial anisotropy dielectric plate and the transformation between spherical vector wave function and column vector wave function,the analytical solutions of scattering field of vortex electromagnetic wave near field irradiation of metal plate,dielectric plate and metal sphere are derived by using continuity boundary condition.The amplitude and phase distribution of near field scattering of target and the variation of oam mode are analyzed.The scattering field of metal conductor is further analyzed by simulation and experimental measurement. |
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