Design and Experimental Validation of a Through-Quartz Via-Based LC RIS for Dual-Polarization Beam Steering in Sub-Terahertz Bands

This paper presents a liquid crystal (LC)-based reconfigurable intelligent surface (RIS) capable of simultaneously achieving dual-polarization conversion and beam steering, enabled by through-quartz vias (TQVs). The proposed RIS offers two primary functionalities-dynamic beam steering and polarization conversion-both of which are validated through full-wave simulations and experimental measurements. A tunable LC layer is employed as the dielectric substrate for each unit cell to facilitate beam steering, while bias lines are used to apply external electric fields to the LC medium. To prevent degradation in polarization conversion performance, the bias lines are connected to the patterned copper structures via TQVs embedded within the quartz substrate. The quartz substrate is perforated using a precision sanding technique to form the vias. A 50×50-element LC-based RIS is fabricated using a standard display manufacturing process to ensure uniform LC layer thickness across the array. The results demonstrate that the polarization of an incident wave is converted to its orthogonal counterpart upon reflection from the proposed RIS. Furthermore, by implementing a phase gradient spanning 137∘ across the unit cells, anomalous reflection is achieved. Comparative measurements with and without the RIS confirm that the received power is significantly enhanced in the direction corresponding to the RIS-engineered reflection angle.