基于编码超表面的太赫兹宽频段雷达散射截面缩减的研究

本文设计了一种柔性, 非定向低散射的1bit编码超表面, 实现了太赫兹宽频带雷达散射截面的缩减. 这种设计基于对“0”和“1”两种基本单元进行编码, 其反射相位差在很宽的频段范围内接近180°, 为一种非周期的排列方式, 该电磁超表面使入射的电磁波发生漫反射, 从而实现雷达散射截面的缩减. 全波仿真结果表明, 在垂直入射条件下, 编码超表面的镜像反射率低于-10 dB的带宽频段范围为1.0-1.4 THz, 该带宽内超表面相对同尺寸金属板可将雷达散射截面所减量达到10 dB以上, 最大缩减量达到19 dB. 把柔性编码表面弯曲在直径为4 mm的金属圆柱面上, 雷达散射截面的所减量高于10 dB以上的带宽频段范围为0.9-1.2 THz, 仍然可实现宽频带缩减特性. 总之, 编码超表面为调控太赫兹波提供一种新的途径, 将在雷达隐身、成像、宽带通信等方面具有重要的意义.

A coding metasurfaces used for wideband radar cross section reduction in terahertz frequencies

In this paper, we propose a flexible, non-directional lowering scattering 1 bit coding metasurface which can significantly reduce the radar cross section (RCS) within an ultra wide terahertz (THz) frequency band. The total thickness of the coding metasurface is only 40.4 μm. The 1 bit coding metasurface is composed of “0” and “1” elements. And the “0” and “1” elements of metasurface are realized separately by a substrate without any metallic covering and that with a square metallic ring covering, the reflection phase difference of the two elements is about 180 degree in a wide THz frequency range. The theoretical, analytical, and simulation results show that the coding metasurfaces simply manipulate electromagnetic waves by coding the “0” and “1” elements in different sequences. Specific coding sequences result in the far-field scattering patterns varying from single beam to two, three, and numerous beams in THz frequencies. The metasurface with the numerous scattering waves can disperse the reflection into a variety of directions for non-periodic coding sequence way, and in each direction the energy is small based on the energy conservation principle. Full-wave simulation results show that the reflectivity less than -10 dB for coding metasurface can be achieved in a wide frequency range from 1-1.4 THz at normal incidence, and the RCS reduction as compared with a bare metallic plate with the same size is essentially more than 10 dB, in agreement with the bandwidth of reflectivity being less than -10 dB; the maximum reduction can be up to 19 dB. The wideband RCS reduction results are consistent with the bandwidth of 180 degrees phase difference between the two elements “0” and “1”. This wideband characteristic of RCS reduction can be kept up as the coding metasurface is wrapped around a metallic cylinder with a diameter of 4 mm. The presented method opens a new way to control THz waves by coding metasurface, so it is of great application values in stealth, imaging, and broadband communications of THz frequencies.