Analysis And Design Of Broadband Electromagnetic Metasurface For RCS Reduction

The main parameter of the radar stealth performance of military targets is Radar Cross Section(RCS).Radar stealth materials are widely used because of their ability to reduce RCS.As a new type of structural material,the electromagnetic metasurfaces has attracted attentions because of its good performance in regulating electromagnetic waves.In this paper,based on the equivalent circuit design and impedance matching theory used in Frequency Selective Surface(FSS),broadband Phase Gradient Metasurface and Polarization Conversion Metasurface for C band and X band RCS reduction(RCSR)are designed.The main work of this article can be summarized as follows:First of all,the equivalent circuit design and the theory of impedance matching are introduced.The generalized Snell's law is introduced to explain how Phase Gradient Metasurfaces realize the abnormal reflection.The conditions of the abnormal reflection are discussed using the metal patch metasurface as an example.From the perspective of reflection phase,the principle of Polarization Conversion Metasurfaces to regulate the polarization of electromagnetic waves is analyzed.Secondly,a cross-shaped Phase Gradient Metasurface unit was designed by the equivalent circuit method and a two-unit metasurface array was proposed which was composed of the proposed cross-shaped unit and no-pattern unit.The effect of the arrangement of the units on the RCS reduction was investigated.The influence caused by the number of units included in an array cell was discussed.The changing trend of the main lobe angle is illustrated by the scatter pattern.Based on the cross-shaped pattern with the circular gap,fourunit Phase Gradient Metasurfaces were designed,and different equivalent circuits were proposed according to different units.The four units maintain a phase gradient of 90° in 4-12 GHz,forming different metasurface arrays which achieve broadband and stable RCS reduction.The influence of the arrangement on the abnormal reflection is analyzed based on the bi-station scattering pattern.Furthermore,a new design method,which the original unit will be transformed,was used to design the Polarization Conversion Metasurface unit.With it,the equivalent circuits corresponding to the two polarization directions can be quickly obtained.A metasurface unit based on circular rings was designed to achieve the broadband polarization conversion.The conversion ratio is higher than 90 percent in the work band.Based on this,a metasurface array with abnormal reflection performance was designed,and a new type of rotating arrangement is proposed,which has better RCS reduction performance than the traditional chessboard arrangement.Finally,combining the concept of FSS absorbers and electromagnetic metasurfaces,the metasurfaces combining absorption and abnormal reflection performance was designed.First,a four-unit resistive Phase Gradient Metasurface was designed.The reflection coefficients of the four units remain approximate in a wide band,and the reflected phase gradient of 90° is realized.The metasurface arrays achieve broadband RCS reduction.The lumped resistances were added to the square ring pattern to design the Polarization Conversion Metasurface unit.The metasurface arrays formed by the proposed units also achieve broadband RCS reduction.The bi-station scattering patterns show that the reflected energy above the two types of structure was greatly reduced,so that the simultaneous absorption and abnormal reflection is realized.