A Fully Screen-Printed Vanadium-Dioxide Switch-Based Wideband Reconfigurable Intelligent Surface for 5G and Beyond

Reconfigurable intelligent surfaces (RISs) suffer from high switch costs and complex switch integration with electromagnetic (EM) structures. In this article, we propose solutions to both of the abovementioned problems by screen printing of low-cost vanadium-dioxide (VO2) switches. The VO2 ink has been prepared in-house and batches of switches have been printed and integrated with the resonator elements. Screen printing is suitable for low-cost and large-area manufacturing, and thus, these VO2 switches are a fraction of the cost of commercial switches. Furthermore, the printing of these switches directly on metal patterns negates the need for any minute soldering of the switches. To avoid the complications of multilayer printing and realizing the RIS without vias, the resonators and the biasing lines are realized on a single layer. However, this introduces the challenge of interference between the biasing lines and the resonators. We address this by integrating bias lines into the resonator design. By adjusting the unit cell periodicity and the dimension of the H-shaped resonator, we achieve a 220°–170° phase shift from 23.5 to 29.5 GHz covering both 5G n257 and n258 bands. Inside the wide bandwidth, the maximum reflection magnitude in the <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> state is 74% and is 94% in the <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> state. The RIS array comprises <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20\times 20$ </tex-math></inline-formula> unit cells (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.54\lambda ^{2} \times 4.54\lambda ^{2}$ </tex-math></inline-formula> at 29.5 GHz). Each column of unit cells is serially connected to a current biasing circuit. To validate the array’s performance, we conduct full-wave simulations as well as near- and far-field measurements. The fully printed array shows signal enhancements of around 8–10 dB, validating its effectiveness.