| Metamaterial is a kind of brand-new material obtained by man-made,which has unique physical properties,so it has attracted wide attention all over the world.Through different changes and optimization of the parameters of its structure,it can obtain the unique physical properties that the existing materials do not have.Electromagnetic metamaterials have changed the traditional cognition of materials,greatly promoted the understanding of materials in human society,opened up one or even several new research spaces,and have great potential for development in the fields of stealth of military equipment and civil communications.At present,the performance of metamaterial absorbers developed in the world is still very poor,difficult to conformal,and opaque.Given these shortcomings that hinder the development of research,this paper takes the working mechanism of metamaterial absorbers on incident electromagnetic waves as a starting point.A kind of metamaterial absorber based on a composite tree resonant structure is simulated and fabricated,and then it is assembled and combined with a microstrip antenna.The goal of reducing the in-band radar cross-section(RCS)of the microstrip antenna is achieved,and the feasibility of the metamaterial absorber in the field of antenna stealth is verified.The main tasks are as follows:(1)A kind of metamaterial absorber based on a composite tree resonant structure is designed.The working mechanism of broadband absorption is verified by analyzing the distribution of surface electric field and current.In the broadband of 13.68GHz-71.6GHz,the absorption performance is more than 90%.Transverse magnetic waves and transverse waves can obtain high absorption performance at large polarization angles and incident angles and are utterly insensitive to polarized incident waves.The equivalent medium theory is used to verify its working mechanism,and the S-parameter inversion method is used to analyze the effect of electromagnetic parameters on its absorption performance.After that,the physical samples were made by micromachining technology.(2)The practical application value of metamaterial absorbers in the field of antenna stealth(RCS reduction)is studied.Taking the coaxial fed microstrip antenna as a reference,the designed metamaterial absorber is loaded around the radiation patch of the microstrip antenna,and the absorbing frequency band of the metamaterial absorber covers its working frequency band.According to the theoretical knowledge of RCS,this paper explores its effect on the performance of the antenna.In these two cases,the radiation performance of the antenna and the trend of in-band RCS reduction are studied.The simulation results show that in a wide range of angular domains,the performance of the antenna itself does not change after loading the metamaterial absorber,but the reduction effect of the RCS in the band is obvious under different polarized incident waves.The whole sample of the combination of the metamaterial absorber and the antenna is made.(3)The actual test of the prepared object is carried out in the free space system,and the results show that the absorber sample achieves a high absorptivity of more than 90% in the working frequency band of 13.8GHz-64.7GHz.At the same time,the overall transparency of the sample is tested by using solar film tester equipment.In the band that can be perceived by human eyes(380-780nm),the overall light transmittance of the sample is more than 66%,which meets the standard of high absorption performance and high transparency of the absorber in practical application;the performance of the antenna before and after loading the metamaterial absorber is tested in the microwave darkroom test platform.There is little difference between the test and simulation results,which verifies the feasibility and application value of metamaterial absorber in the field of RCS reduction and improving the stealth performance of the antenna. |
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