A 2-bit Tunable Unit Cell for 6G Reconfigurable Intelligent Surface Application
Luis G. da Silva, Pei Xiao, Arismar Cerqueira S.
Abstract
This paper presents a 2-bit unit cell for reconfigurable intelligent surface (RIS) applications of beamforming and beam-steering in the frequency range 2 (FR2) for the fifth generation of mobile communications (5G). The proposed RIS unit cell is based on a printed split-ring resonator (SRR) loaded with a varactor diode, which connects two circular loops at the top and a ground plane at the bottom, resulting in a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.245\times 0.245\lambda_{0}$</tex> total area. The entire unit cell element encompasses four conducting layers, in which the first two ones form the SRR, whereas RF chokes are printed at the middle layer to isolate the DC circuit and the bias lines are routed at the fourth layer. The RIS unit cell design has been conceived using the full-wave electromagnetic solver ANSYS HFSS. Its numerical results demonstrate reflection phase shift up to 270° and reflection magnitude higher than 0.5 at 24.5 GHz. The proposed reconfigurable intelligent surface might be applied to future wireless communication systems, planar antenna reflectors, and vortex beam generation.