Sub‐THz Multifunctional Metasurfaces for Independent Transmission or Reflection Phase Manipulation

This paper presents the analysis, synthesis, and characterization of a novel dual‐band sub‐THz metasurface with multi‐functional capabilities, suitable for use in either RIS, transmitarray or reflectarray applications. The proposed metasurface architecture provides full‐space beam control with dual‐band operation, covering both the W‐ and D‐bands in the lower frequency range and the H‐band in the upper frequency range. An analytical approach based on the transfer‐matrix method is used to study the transmission and reflection properties of the periodic meta‐atom or unit‐cell, which is also illustrated through an equivalent circuit model. This analysis allows determining the necessary conditions for tuning the transmission and reflection phases while maintaining insertion and reflection losses as low as possible. Based on the proposed metasurface, dual‐band transmissive and reflective quasi‐optical antennas, are synthesized, optimized, and fabricated using a low‐cost fused silica‐based photolithographic process. Experimental results demonstrate promising performance, particularly in terms of high‐gain and wide gain bandwidths, confirming the potential of this metasurface design for sub‐THz applications.