Concept of a 1-Bit Reconfigurable Intelligent Surface for Future Applications: Design, Optimization, and Array Size Impact Analysis

Antenna arrays play a key role in current wireless systems, particularly in 5G FR2, where beamforming helps overcome high propagation losses. However, these arrays are active systems, requiring power amplifiers and complex RF chains. As a low-cost and energy-efficient alternative for future 6G technologies, passive Reconfigurable Intelligent Surfaces (RIS) have gained attention. RIS structures can enhance signal directionality through beam collimation using tunable reflective unit cells. This work presents the design and optimization of a 1-bit RIS unit cell operating at 5.8 GHz. The cell consists of a rectangular patch with a single PIN diode, and its performance is evaluated using a cost function that balances phase shift and reflection coefficient (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$S_{11}$</tex>) in both diode states. The selected configuration achieves a phase difference close to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$170^{\circ}$</tex> with minimal variation in <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$S_{11}$</tex>. Floquet port simulations confirm the phase and reflection behavior of the unit cell. Additionally, RIS arrays of 100, 400, and 1600 elements are simulated to analyze beamforming performance at 30°. The smallest array exhibits side lobes, while larger arrays produce well-defined, directive beams. The results show that 1-bit RIS arrays, when sufficiently large, can achieve efficient passive beam steering with low complexity, making them promising for mmWave and sub-THz systems in future wireless communications.