Research On Electromagnetic Metasurfaces For Electrically Tunable And Conformal Design Of PIN Diode Loading

In recent years,metasurfaces have attracted the attention of scholars because of their wide applications.This thesis focuses on reconfigurable metasurfaces,whose working status can be dynamically controlled,so that the same metasurface can achieve different electromagnetic(EM)responses,and considering that modern weapon platforms are often non-planar,the conformal metasurface was studied in this thesis.Firstly,a dual-band reconfigurable metamaterial absorber with real time coding radar cross section(RCS)was proposed in the chapter 3.The unit cell of the FSS is composed of an annular ring and a meander cross dipole.The dual-band resonance frequencies are reconfigurable by switching the PIN diodes embedded in the unit cell.A novel biasing network is designed for the fabricated reconfigurable FSS absorber,thus the scattering field from each unit cell can be coded independently by switching the “on” and “off” states of the unit cells by a programmable field programmable gate array(FPGA).The RCS from the metamaterial absorber can be coded real time by controlling the number of PIN showing on/off,which is elaborately programmable within the range of 33 d B in S band and 26 d B in X band,respectively.Both numerical and experimental results under normal incidence demonstrate our design.Then,the traditional array theory is extended to conformal coding metasurface for controlling the wavefront,where the relationship between wavefront and conformal metasurface is derived in the chapter 4.Based on the optimization algorithm and far-field scattering pattern analysis,a conformal metasurface with broadband low-scattering is designed.However,the mutual coupling is not considered when using far-field scattering pattern analysis.Therefore,for some frequencies the full-wave simulations do not meet our design requirements.We use the space mapping algorithm for further optimization in this work.By establishing a mapping relationship between coarse model(genetic algorithm and analytic formulations)and a fine model(the full wave method of moments),this relationship can be used to transform the direct optimization of complex and time-consuming fine models into the optimization and update of simple and fast coarse models.A conformal coding metasurface with RCS reduction of 10 d B from 6 GHz to 16 GHz is demonstrated to validate the design method.Finally,reconfigurable metamaterial absorber and conformal metasurface design method proposed in this paper are promising for many potential applications in stealth protection.It is of great significance to improve the survivability and penetration ability of combat platforms.