Characteristic Mode Theory Based Metasurface For Wideband RCS Reduction Of Antenna

With the rapid development of radar detection technology in recent years,the importance of radar stealth technology has become increasingly prominent.For the low scattering platform,reduction of antenna RCS is particularly important.With the development of computational electromagnetics,characteristic mode theory is widely applied to study radiation and scattering of the antenna.The use of characteristic mode theory can explore the intrinsic properties of the target object itself.There are some unique advantages in the application of characteristic mode theory to the study of the radiation and scattering problems of antennas.Bsed on it,the characteristic mode theory has been extended to study the RCS reduction of the object in the thesis.The detailed work are summerized as follows:1.A new method based on characteristic mode theory called mode cancellation technique has been proposed for antenna RCS reduction.Firstly,some important physical quantities in the characteristic mode theory are discussed.Based on it,the concept of mode cancellation has been introudced.Specifically,different working modes are cancelled with each other to achieve the reduction of the RCS.Subsequently,the characteristic mode theory is used to analyze and design the metasurface units with mode cancellation characteristics.The RCS reduction curve of the proposed metasurface is obtained by the HFSS simulation,and the RCS reduction performance can be achieved in a wide band from 6.2GHz to 22.1GHz,which verifies the effectiveness of the proposed mode cancellation method.Finally,a rectangular microstrip antenna is used as a reference antenna,and the designed metasurface is located around it.The radiation and scattering properties of the reference antenna and the metasurface-loaded antenna are simulated and measured.The measurement and simulation results are given to demonstrate that the introduction of the metasurface has no effect on the radiation performance of the antenna,and the gain in the working frequency band can be enhanced,and the RCS reduction is achieved in a broad band covering 6.4GHz-21.4GHz.After that,the simulation obtained the 3D RCS diagram of the reference antenna and the super-surface antenna at the normal incidence of electromagnetic waves and incident at-20°,and demonstrated the RCS reduction effect of the metasurface antenna under oblique incident conditions.2.A new method based on characteristic mode theory named mode conversion technique is proposed to reduce the RCS of the object.Firstly,an elliptical microstrip element is designed as an example to demonstrate the concept of mode conversion.Then,the metasurface unit with the mode conversion is designed by using the characteristic mode analysis.The amplitude of the mode weighting coefficience and the distribution of the complex mode current are used to determine the frequency band of the mode conversion.By reasonable arrangement of the designed metasurface units the metasurface can realize the RCS reduction.And the RCS reduction performance of the mode conversion metasurface is verified by HFSS.Finally,a rectangular microstrip antenna is designed as a reference antenna,and a mode conversion unit is arranged around it to form a metasurface antenna.The radiation and scattering performances of the reference antenna and the metasurface antenna are obtained by simulation.The simultion results show that the introduction of the mode conversion metasurface has no effect on the radiation performance of the antenna,and can achieve a 10-d B RCS reduction in a frequency band from 8.8GHz to 22 GHz.