| Based on the holographic principle,the circularly polarized metasurface antenna can realize electromagnetic wave radiation characteristics of different functions by constructing the interference plane formed by the source field and the target radiation field.This multifunctional metasurface structure can be widely used in electromagnetic stealth,navigation,satellite communication and other scenarios.The thesis summarizes the research background,research significance and related research development of domestic and foreign,and deduces the relevant basic theories of the thesis.At the same time,with the topic of conformal design based on holographic metasurface,the cylindrical/spherical holographic metasurface antenna is mainly studied,and its radiation characteristics are further analyzed.The main research contents of the thesis are as follows:1.Analysis of impedance modulation principle and radiation mechanism of holographic metasurface.The basic principle of holographic impedance modulation is discussed in detail,the definitions of holographic principle,surface wave and surface impedance are given,and the harmonic theory of periodic structure and the surface theory of sinusoidal impedance modulation are deduced in detail,which are the research basis of this thesis.Then,the radiation mechanism of the holographic metasurface antenna is described in detail,and the conditions for the conversion of surface waves to leaky wave radiation on the holographic impedance surface are clarified.Then,the process of extracting the impedance of the isotropic circular metal patch and the anisotropic element of the circular metal patch with an oblique slot are introduced respectively,and the mapping relationship between their physical characteristics and impedance characteristics at 15 GHz is given.2.Research on cylindrical holographic circularly polarized metasurface antenna based on holographic principle.A new H-shaped slot circular metal patch anisotropic element is proposed and applied to the design of conformal holographic metasurface antenna,which can achieve high aperture efficiency and circular polarization purity.First,the impedance modulation expression for radiating circularly polarized waves on a cylindrical surface is deduced,so that when the metasurface structure is irradiated with a surface wave generated by a monopole feed,the anisotropic impedance element can change the electromagnetic wave according to the designed parameters radiates a high-purity circularly polarized beam in any direction of the cylindrical surface.Secondly,starting from the specific performance parameters of the antenna,we analyze the beam scanning characteristics of the cylindrical holographic metasurface antenna when the curvature radius is fixed and the circular polarization radiation characteristics when the curvature changes at 15 GHz.The circular polarization purity of the antenna reaches 98 % or more,the simulation aperture efficiency reaches 27%.In order to verify the correctness of the theoretical analysis and simulation,the radiation characteristics and aperture utilization of the cylindrical holographic metasurface antenna with a curvature radius of 75 mm were processed and tested.The surface can convert incident surface waves into high-purity circularly polarized radiation.3.Research on spherical holographic metasurface circularly polarized antenna based on holographic principle.A holographic metasurface impedance modulation formula based on the principle of interference field superposition is proposed,and it is applied to the spherical conformal holographic metasurface structure,which can realize dual circularly polarized and dual beam radiation in any direction.First,for the cylindrical conformal case of compensating the phase of the target radiation field in one dimension,we extend the conformal surface to a spherical surface that compensates the phase in two dimensions.By deriving the holographic metasurface impedance modulation formula based on the superposition of interference fields,the dual circularly polarized and dual beams are radiated on the spherical surface.Secondly,by changing the parameters in the impedance modulation method,the spherical holographic metasurface antenna can realize dual circular polarization dual beam radiation in any direction,and the circular polarization purity of the antenna radiation beam reaches more than 97.5%.According to our proposed design principle,a corresponding simulation case is given.The metasurface antennas in the case all realize the perfect regulation of surface waves. |
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