Enhanced terahertz diffuse scattering through convolutional coding on broadband polarization conversion metasurface

Future 6 G systems integrating joint communication and sensing demand more attention to terahertz diffuse scattering. Despite coding metasurface exerting prevailing capabilities of regulating diffuse scattering of electromagnetic (EM) waves in a flexible digital manner, cost-effectiveness, non-structural reconfigurability, broadband, and wide-angle high-efficiency in terahertz range require further research. This paper proposes an ultra-wideband and high-efficiency reflective linear polarization conversion metasurface to reduce radar cross-section (RCS). Simulation results show that the polarization conversion ratio (PCR) is above 90% in an ultra-wideband from 0.24 THz to 0.52 THz, and the fractional bandwidth reaches 74%. Taking the advantages of high-efficiency and broad-bandwidth polarization conversion, the meta-element and its mirror-symmetry element form the 1-bit digital metasurface. Further comparative study shows the feasibility of enhancing the RCS performance by implementing a convolutional process among different diffusive coding patterns. The measured results show that the reflection amplitude of the three coding metasurfaces is less than -19 dB when the incident angle is 15°. Additionally, compared with the Golay-Rudin-Shapiro (GRS), the convolutional coding metasurface of GRS + Cross and GRS + Checkerboard effectively suppress specular reflection, achieving a maximum suppression amplitude of 17 dB. The proposed metasurface holds significant potential for manipulating terahertz waves, offering promising applications that contribute to RCS reduction, computational imaging, and multi-beam shaping.