| The vortex wave is a non-planar electromagnetic wave carrying orbital angular momentum.It has multiple orthogonal modal and helical forms of equal phase planes,and can be used in wireless communications,radar imaging,target detection and other fields.The generation and regulation of vortex waves are the frontier and hot topics in the field of electromagnetic research,and have important research value.Electromagnetic metasurface have attracted the attention of researchers because they can flexibly adjust the electromagnetic wave front and have an abnormal electromagnetic response characteristic to electromagnetic waves.It can be designed according to human requirements,and the sub-wavelength units are arranged in different regular cycles to control multiple index parameters of electromagnetic waves.Starting from the electromagnetic metasurface,this thesis mainly proposes two new methods of design and regulation of vortex waves,and carries out processing and experimental tests.The main research contents are as follows:1.Based on the phase-controlled metasurface array,the vortex wave and Bessel beam modulators are studied,and the circularly polarized beam control in both transmission and reflection directions is realized at the same time.First,using the Pancharatnam-Berry phase principle,combined with the compensated vortex phase,vortex waves with different circular polarizations are simultaneously generated in the transmission and reflection directions,the gains are all above 18 d B,and a better circularly polarized vortex phase is generated.Secondly,a cone-shaped phase distribution is loaded,a zero-order Bessel beam generator is designed,and its electromagnetic characteristics at 10 GHz non-diffraction and selfconvergence are verified.Finally,the vector superimposes the cone phase and the vortex phase to design a full-space electromagnetic metasurface that generates a first-order Bessel beam.From the electric field distribution,after the cone phase is loaded,the diffraction divergence effect of the vortex wave significantly reduced,and the phase of the circularly polarized vortex is intact.The experimental and simulation results of the three electromagnetic metasurface design models proposed above are in good agreement,and all meet the theoretical design requirements.2.Based on the holographic impedance surface,the scalar and tensor impedances are used to control circularly polarized waves.Holographic impedance surface has the advantages of low profile and easy conformal,and belongs to the category of electromagnetic super surface.Use the interference thought of reference wave and target radiation wave to perform periodic impedance modulation.Firstly,a scalar circular polarization impedance surface design model is proposed,and the impedance distribution is modified based on the traditional holographic impedance.At a non-phase matching frequency of 12 GHz and a main beam direction of 45 degrees,the maximum gain of the left-hand circularly polarized wave component is 19.2 d B,thus realize the control of scalar impedance to the polarization of electromagnetic waves.Secondly,combined with the idea of scalar impedance extraction and modulation,a tensor impedance surface is designed to regulate right-hand circularly polarized vortex waves.At the operating frequency of 17 GHz,the right-hand circularly polarized component has a maximum gain of 17.8 d B.Combined with the near and far field characteristics,it is confirmed that the tensor holographic impedance surface can adjust the right-hand circularly polarized vortex wave.From the simulation results,the two holographic impedance surface antennas meet the requirements of theoretical design. |
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