Study On Beamforming Of Periodic-impedance Modulated Metasurfaces

Based on the traditional single-beam periodic impedance modulated surface,this thesis,combining the shared aperture method of the average impedance value of modulated metasurfaces and the beam synthesis idea,realizes one-dimensional flat-top and double-beam.Further,by employing the fan-shaped architecture,the beam-splitting problem that exists in the traditional modulated metasurface is released.Moreover,two methods are proposed to increase the antenna gain and improve the beamforming performance.Firstly,the design method of a high-gain single-beam periodic impedance modulation surface based on amplitude and phase modulation is discussed.Compared with the design of the traditional holographic impedance modulation surface,the aperture efficiency is greatly improved.Secondly,based on the single beam modulated metasurface with shared aperture method of the average impedance value of modulated metasurfaces as well as the beam synthesis idea,one-dimensional flat-topped beamforming along azimuth and elevation directions in a certain range are studied.On the other hand,through the global optimization to the final modeling parameters related to the impedance modulation coefficient,the modulation coefficient of the whole array is improved to improve the radiation gain and beam-forming performance.Thirdly,to release the problem of beam-splitting along with the operating frequency of the traditional full impedance modulation surface,the fan-shaped structure that only supports the forward wave radiation is proposed,where EBG structures are loaded on the fan-shaped structure to control the energy distribution to enhance the aperture efficiency and radiation gain.Furthermore,one-dimensional flat-topped beamforming in the azimuth direction is developed by using the fan-shaped modulation metasurface with EBG loading.Finally,with uniform EBG structure loading on the edge of a traditional circular modulated metasurface,low energy utilization and edge scattering problem of a small aperture modulated metasurface is solved.A dual-beam modulated metasurface with high gain and high aperture efficiency is further developed.With this method and by changing the aspect ratio of the utilized patch element,the radiation gain of a traditional dual-beam modulated metasurface can be greatly enhanced.Further,this method is employed to design a fan-shaped modulated metasurface with good performance.