Research On Design And Application Of Frequency-Space Two Dimensional Reconfigurable Metasurface

Under the background of "Internet of Everything",all kinds of communication equipment are growing explosively,and spectrum and space resources have become extremely tight.Researchers have tried to use frequency-space multiplexing technology to solve the problems in the frequency and space domains.As a special kind of modulation equipment,the frequency-space two-dimensional metasurface can modulate electromagnetic waves in two dimensions,which provides a new idea for the development of existing communication systems and has important research significance.Based on the study of frequency-space twodimensional reconfigurable electromagnetic metasurface,this thesis proposes several novel multi-functional electromagnetic modulation surfaces for the application of electromagnetic wave polarization direction conversion,beam dynamic scanning,orbital angular momentum vortex electromagnetic wave generation,near-field wireless energy transmission,transmission-reflection wavefront control,etc.At the same time,polarization modulation strategy is also introduced to expand the functions of such devices with the same aperture.On the premise of ensuring that different functions do not interfere with each other,the aperture utilization of the metasurface is greatly improved.In addition,the active tunable devices loaded on the metasurface build a bridge between the physical material and the digital world,which provides the basis for the perception and interactivity of the surface.The main work of this thesis is as follows: 1.Research on frequency domain reconfigurable line-to-circular polarization converter loaded with PIN diode.By adjusting the “ON” or “OFF” state of the diode,the line-tocircular polarization converter can dynamically switch the operating frequency band.On the one hand,the reconfigurable polarization converter can convert x-polarized or y-polarized waves into left-hand circularly polarized or right-hand circularly polarized waves from 5.13 GHz to 6.72 GHz,and the 3d B axial ratio relative bandwidth can reach up to 26%.This design solves the problem of little working bandwidth of the existing reconfigurable polarization converters.On the other hand,the converter has good angular stability,and maintains stable conversion performance within the incident angle range is ±30°.2.Research on frequency-spatial-domain two-dimensional reconfigurable metasurface.In the frequency domain,the reconfigurable metasurface has three main functions: polarization selection,frequency reconfigurable polarization conversion and polarization reconfigurable.Polarization inversion modulation technology is introduced into the design,so that the metasurface can achieve line-to-circular polarization conversion under the excitation with different polarization directions,and the polarization direction of the reflected circularly polarized wave can be inverted(a left-hand circularly polarized wave turns into a right-hand circularly polarized wave,and a right-hand circularly polarized wave turns into a left-hand circularly polarized wave).In the space domain,the metasurface can be programmed to realize multiple functions such as two-dimensional dynamic scanning of beam,continuous mode switching of vortex wave with orbital angular momentum and adjustment of special scattering beam etc.The simulation calculation results and experimental results prove that the reconfigurable metasurface can realize different electromagnetic wave modulation functions under the same aperture,which lays the foundation for the design of intelligent surface.3.Research on nonpolarized modulated transmission-reflection reconfigurable metasurface.The transmissive and reflective states of the metasurface can be fully actively controlled.The 1-bit transmission function and 1-bit reflection function are designed in two frequency bands,respectively,so that the two functions of the unit do not interfere with each other and have good radiation performance.In this paper,the performance of the metasurface is verified from the aspects of the unit structure,modulation method,analysis optimization and actual measurement.This metasurface can modulate its transmission phase or reflection phase in real time without depending on the polarization direction of the incident wave,which solves the shortcomings of the traditional transmission-reflection metasurface.In addition,the height of this metasurface is only 0.09λ,which greatly improves the integration of the surface,and provides a new direction for the realization of completely autonomous control of transmission-reflection metasurface devices.