Design Of Luneburg Lens Antennas Based On Electromagnetic Metamaterials

Usually Luneburg lenses have broadband,high gain and multi-beam scanning characteristics,which can be used as wide-angle scanning antennas.In practice,it is difficult to find the materials with continuous distributions of refractive index.Even if discrete shells made of dielectric,liquid,or composite material can be used to roughly estimate the lenses,their manufacturing process and precision are relatively high.By using the electromagnetic metamaterials to manufacture the lens,and arranging the metamaterial units with different dielectric constant values according to the required dielectric constant distribution of the Luneburg lens,the designed lens can be obtained.The design process is simple and convenient.3D printing technology is fast and efficient,which solves the difficult problem of lens processing.Therefore,in this thesis,taking the Luneburg Lens antenna as the research object,a three-dimensional Luneburg lens antenna based on the gradient index metamaterials and a flat Luneburg lens antenna with Luneburg lens antenna are designed and implemented.Main contributions of this thesis can be summarized as follows.1.Based on the graded index metamaterial,a three-dimensional Luneburg lens antenna working in the C-band is proposed.By using the photonic crystal structure,the dielectric permittivity distribution condition of the lens with a gradient refractive index is realized.The dielectric column of the diamond structure is selected as the photonic crystal unit cell,and the relative permittivity of the photonic crystal unit cell is controlled by radius of the dielectric column.The S-parameter inversion method is used to determine the relationship between radius of the dielectric column of the unit cell and the relative permittivity.A lens with a diameter of 24cm is then designed.The lens is discretized into 917 units,and the unit size is 20mm.The radius of each unit dielectric column is set according to the required permittivity distribution of the Luneburg lens,and a kind of diamond is constructed.A novel type of Luneburg lens antenna is composed of structural dielectric column arrays.The actual measurement results show that the designed antenna can operate in about 22% frequency band,the antenna efficiency is 49%,and gains of the antenna in the frequency band range between 17.9-18.9dBi(4GHz-5GHz),which is basically consistent with the simulation results.2.Based on the periodic structure materials,an X-band flat-plate Luneburg lens antenna is proposed.According to the basic principle of optical transformation,an appropriate transformation function is selected to convert the spherical Luneburg lens into a flat Luneburg lens.The dielectric substrate is used to print the regular hexagonal patch as the metamaterial unit,and the required permittivity distribution of the lens is realized by changing dimensions of the regular hexagons.A novel flat Luneburg lens with a thickness of 8mm,an aperture of 100×92mm~2 and a focal length of 50 mm is then designed.The lens is divided into 11 layers of gradient index metamaterials,and each layer is discretized into 8×10 units.The planar permittivity distribution is used to determine dimentions of the hexagons,and the dual-polarized crossed dipole antenna working in the 9GHz-11GHz band is used as the feed.The measurement results show that the designed antenna can operate in about 20% frequency band,its antenna efficiency is 60.17%,its gains in the frequency band range between 17.8-19dBi(9GHz-11GHz),and its ±45°linearly-polarized beam scanning angles are ±32°and ±33°respectively.