This paper presents the first experimental validation of reflective near-field beamfocusing using a reconfigurable intelligent surface (RIS). While beamfocusing has been theoretically established as a key feature of large-aperture RISs, its practical realization has remained unexplored. We derive new analytical expressions for the array gain achieved with a $b$-bit RIS in near-field line-of-sight scenarios, characterizing both the finite depth and angular width of the focal region. The theoretical results are validated through a series of measurements in an indoor office environment at 28 GHz using a one-bit 1024-element RIS. The experiments confirm that beamfocusing can be dynamically achieved and accurately predicted by the proposed simplified analytical model, despite the presence of hardware imperfections and multipath propagation. These findings demonstrate that near-field beamfocusing is a robust and practically viable feature of RIS-assisted wireless communications.

翻译：本文首次通过实验验证了利用可重构智能表面实现反射式近场波束聚焦。尽管波束聚焦在理论上已被确立为大孔径RIS的关键特性，但其实际实现仍未被探索。我们推导了在近场视距场景下，采用$b$比特RIS所能实现的阵列增益的新解析表达式，刻画了聚焦区域的有限深度和角宽度。这些理论结果通过在28 GHz频段、使用1比特1024单元RIS在室内办公环境中的一系列测量得到了验证。实验证实，尽管存在硬件缺陷和多径传播，波束聚焦仍可动态实现，并能通过所提出的简化解析模型进行准确预测。这些发现表明，近场波束聚焦是RIS辅助无线通信中一个鲁棒且实际可行的特性。