| Metamaterials are composed of a series of subwavelength unit cells with special structure in periodic way.Different unit cells and different spatial arrangements determine the physical characteristics of metamaterials.As two-dimensional metamaterial,metasurface can control the beam by adjusting the amplitude,phase,polarization mode or propagation mode of electromagnetic wave,which has the advantages of simple structure and low loss.In recent years,with the rapid development of electronic technology,the commercialization of 5G technology and the demand for military,there are increasingly higher requirements for the antenna performance.The introduction of metasurface has given the antenna a further improvement in broadband,multi-beam and multi-mode.This thesis studies the application of metasurface in antenna design and proposes four new types of metasurface unit cells.At the same time,the designed unit cells are applied to high-gain antennas,orbital angular momentum communication antennas,and multi-beam antennas.Main contents of this thesis include the following aspects:(1)A new type of multilayer periodic transmission metasurface unit cell is proposed.Through the simulation analysis of the metasurface unit cell,the phase range of unit cell is close to 360° with similar phase curves in the Ku band,and the transmission phase is linear.In order to determine the size of unit cells according to the phase compensation theory,artificial neural network was first introduced to fit the phase size curve.The fitting error was reduced by 88% compared with the traditional fitting algorithm.The metasurface was fabricated and measured in the anechoic chamber.The gain reaches 24.74 dBi at 12.5 GHz.The 1-dB gain bandwidth of the antenna are 11.2%.The measured results agree well with the simulated results.(2)A single-layer ultra-thin transmission metasurface is presented to generate a multi-mode orbital angular momentum beam.The unit cell realizes the transmission phase range close to 360° by loading metal vias through the substrate.Based on the analysis of the orbital angular momentum generation principle,the phase distribution required for the metasurface is calculated with the phase compensation theory.Finally,two modes of 0-mode and 1-mode orbital angular momentum metasurface antennas are designed.In 0 mode,the maximum gain of the antenna is23.1dBi,and the gain bandwidth is 13%.The maximum gain of the antenna in mode 1 is 17.2dBi,and the beam divergence angle is about 5°.The simulated results verify the effectiveness of the design scheme,and it can predict that metasurface have great application prospects in orbital angular momentum communication antennas.(3)In order to realize the multi-beam radiation of the antenna,a transmission metasurface multi-beam antenna is designed.A transmission metasurface unit cell is designed to achieve a transmission phase change close to 360° at 10 GHz.The phase distribution of the four-beam metasurface antenna was calculated based on the aperture field superposition method and phase compensation.The error between the simulated and target values of the beam pointing of the four beams was 2.8°.In order to realize the integration of transmitting and receiving of antenna system,a dual-frequency transmission metasurface unit cell is designed to achieve a phase range close to 360° at 23 GHz and 33 GHz,respectively.According to the phase distribution of the dual beams,the metasurface is configured.Finally,the errors between the simulated and target values of beam pointing are 0.4° and 2.6° at23 GHz and 33 GHz,respectively.It verifies the feasibility of the metasurface in multi-beam antennas. |
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