A I-bit Ultra- Wideband Reconfigurable Intelligent Surface with Multilayer Structure for Beyond 5G

This paper proposes a novel I-bit reconfigurable intelligent surface (RIS) with a multi-layer structure to improve the bandwidth for beyond 5G applications. The proposed RIS operates at the 10 GHz band of 5G-Advanced or 6G. In addition, it comprises <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$16\times 16$</tex> unit cells, in which each unit cell is designed to provide 1-bit reflection phase control corresponding to 2 different reflection phases (0° and 180°). To ensure wideband properties, the unit cell is constructed with a multilayer structure: the top layer, the middle layer, and the bottom layer. The top layer and middle layer contain two resonant patches which are placed on two different height substrates (Rogers R043S0B, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\varepsilon_{r}=3.66, \tan(\delta)=0.0037)$</tex>. These two patches are truncated at two opposite corner pairs to further enhance the bandwidth. An RF choke with a round shape has been integrated into the bottom layer to prevent the DC control signal from interference caused by the RF signal. The final unit cell design has the overall size of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.51\lambda_{0}\times 0.51\lambda_{0}\times 0.14\lambda_{0}$</tex> at 11 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{GHz}(\lambda_{0}$</tex> is the wavelength) The simulation results demonstrate that the proposed unit cell provides 18 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0^{\circ}(\pm 30^{\circ})$</tex> phase change over an ultra-wideband of around 3.31 GHz, which is equivalent to 33% fractional bandwidth. Furthermore, it is demonstrated that the RIS can steer well the beam to the desired direction with proper reflection phase controls.