Dual-Polarized Reconfigurable Intelligent Surface Unit Cell with Single Varactor Diode

In recent years, reconfigurable intelligent surfaces (RISs) have garnered significant interest due to their advantageous properties. An RIS, being a nearly passive surface, can dynamically alter the reflected field, thus enabling anomalous reflection, facilitating the engineering of the radio propagation environment. This paper introduces a novel dual-polarized unit cell designed for use in Reconfigurable Intelligent Surface (RIS) applications. The reconfigurability of the proposed unit cell is achieved through the use of a single varactor diode. Continuous alteration of the reflection phase, up to 360\textsuperscript{o}, for both transverse electric (TE) and transverse magnetic (TM) incident electromagnetic waves is enabled by adjusting the biasing voltage across the diode between 0 and 30 V, which results in a change in diode's capacitance from 2.67 to 0.63 pF. The design of the unit cell incorporates three substrate layers and is optimized for a central operating frequency of 5.3 GHz, with an operational bandwidth of approximately 300 MHz. This study demonstrates the potential of the proposed design in enhancing the performance and versatility of RIS technologies.