Research On Slab Lens Antennas Based On Gradient Index Metamaterial

Gradient Index Metamaterials?GRIN?is a new type of metamaterial,which is composed of a regular arrangement of artificial electromagnetic units with deep subwavelength dimensions.By adjusting the electrical coupling or magnetic coupling of the artificial electromagnetic unit,the control of the permittivity or the permeability is realized,thereby realizing the change of the refractive index of metamaterial.In this paper,a GRIN lens antenna is constructed by gradient of the refractive index of metamaterial,and the modulation of antenna radiation wave is realized in the broadband range.The main research contents of the paper are as follows:?1?The design principle of the GRIN lens antenna is introduced,including the principle of geometric optics and impedance matching theory,and the strict design formula of the focusing and deflection lens is given.In order to achieve a large range of refractive index changes for GRIN lenses,we designed a broadband high refractive index metamaterial.The refractive index of the metamaterial is greater than 10 in the frequency range of 0-11.6GHz,and its trend changes gently with frequency,while the loss of the metamaterial is almost zero.In order to realize the GRIN lenses applications using the high refractive index metamaterials,we first studied the polarization insensitivity and wide-angle incidence characteristics of metamaterials.Then,we study the controllable characteristics of the refractive index of metamaterials,and analyze the influence of the duty ratio of the material unit,the dielectric constant of the dielectric plate,the thickness of the dielectric plate,and the length of the metal patch on the refractive index.?2?A wideband compact circular polarized horn antenna was designed using a GRIN lens.First,the feed device for a wideband compact circular polarized horn antenna was designed,including a TE₁₀-TE₁₁ mode converter and a waveguide circular polarizer.The feed device occupies good performance such as the wide-band,the compact structure,and the easy processing.Then,by using high refractive index metamaterials,we designed a beam-focusing GRIN slab lens that was loaded into a circularly polarized conical horn antenna.So,the directivity of the antenna is improved.The simulation and experimental results show that the radiation performance of the antenna is greatly improved when the focusing lens is loaded to the antenna,and the antenna gets the 3dB axial ratio bandwidth from 4.75GHz to 6.75GHz?relative bandwidth of 34.8%?,with the aperture efficiency greater than 60%and the lens thickness of 0.34₀.Comparing with the same size circular polarized conical horn antenna without lens,the average gain is increased by 3.4dB.Comparing with the conventional circular polarized conical horn antenna with the same aperture size,the vertical size of the horn has been reduced by 54%.?3?The GRIN lens is used to design Ku-band horn lens antennas,realizing different beams of different shapes which include elliptical?round?type and multi-beam lens antennas.Based on the two basic functions of beam deflection and beam focusing,the program of lens refractive index was realized using the MATLAB software.By means of electromagnetic simulation software CST,elliptical beam,circular beam and four-beam antenna are realized.The shape of the beam is stable in the whole Ku-band,the thickness of the lens is thin,and the longitudinal size of the antenna is smaller.