Metasurface-Based Reconfigurable Intelligent Surface With Novel Comb-Shaped Unit Cell Design

Future wireless communication systems like 5G and even 6G have attracted an immense research interest in Reconfigurable Intelligent Surfaces (RISs) with their promising coverage. In this paper, a simulation-based study on metasurface-based design for RIS has been presented, using a Comb-shaped unit cell structure. The unit cell has been simulated for its reflection phase response vs frequency in the mmWave band (24-30 GHz). A commercially available varactor diode has been mounted on the unit cell in the simulation, to provide user-controlled capacitance, which in turn can control the phase delay on the surface. The unit cell has been characterized for its phase response versus capacitance at 27 GHz. From this, a set of capacitances have been chosen that will provide a predetermined phase gradient over the reflectarray constructed using the unit cell. This phase gradient will control the reflected beam tilt angle. From a Bistatic RCS simulation of the structure, for two different phase gradients, the beam tilt angles have been found, which are observed to be very close to the calculated values, thus validating the design.