A Reconfigurable Intelligent Surface for 3.6 GHz Based on a Double Squared Slot Shaped Element

In this paper, a reconfigurable intelligent surface (RIS) designed to operate at 3.6 GHz featuring a double square unit cell layout, is presented. The unit cell includes two varactor diodes, enabling reconfigurable functionality. Two RIS configurations, with dimensions of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5\times 5$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$10\times 10$</tex>, each employing the proposed unit cell, are studied. Simulation results demonstrate the reconfigurability of both configurations, effectively steering incident waves toward specified angles. The <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5 \times 5$</tex> RIS achieved an aperture efficiency of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\eta=42.7\%$</tex> at a reflection angle of 25°, highlighting the unit cell's effectiveness. To validate the design, a prototype of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5\times 5$</tex> fabricated. Preliminary results obtained on the prototype yield to a scanning angle region of 20° with the best performance being achieved on the frequency range from 3.5 to 3.7 GHz.