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

Abstract

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.