We propose a power- and hardware-efficient, pragmatic, modular, multiuser/multibeam array-fed RIS architecture particularly suited to operate in very high frequency bands (high mmWave and sub-THz), where channels are typically sparse in the beamspace and line-of-sight (LOS) is required to achieve an acceptable received signal level. The key module is an active multi-antenna feeder (AMAF) with a small number of active antennas placed in the near field of a RIS with a much larger number of passive controllable reflecting elements. We propose a pragmatic approach to obtain a steerable beam with high gain and very low sidelobes. Then, $K$ independently controlled beams can be achieved by stacking $K$ of such AMAF-RIS modules. Our analysis takes in full account: 1) the near-end crosstalk (NEXT) between the modules, 2) the far-end crosstalk (FEXT) due to the sidelobes; 3) a thorough energy efficiency comparison with respect to conventional {\em active arrays} with the same beamforming performance. Overall, we show that the proposed architecture is very attractive in terms of spectral efficiency, ease of implementation (hardware complexity), and energy efficiency.

翻译：本文提出了一种功率与硬件效率高、实用性强、模块化的多用户/多波束阵列馈电智能反射面架构，该架构尤其适用于极高频段（高频毫米波与亚太赫兹频段），此类频段的信道通常在波束域具有稀疏性，且需要视距传输以达到可接受的接收信号电平。其核心模块为一种有源多天线馈电器，该馈电器包含少量有源天线，并放置于具有大量无源可控反射单元的智能反射面近场区域。我们提出了一种实用化方法以获得高增益、极低旁瓣的可控波束。通过堆叠K个此类有源多天线馈电器-智能反射面模块，即可实现K个独立可控波束。我们的分析全面考虑了：1）模块间的近端串扰；2）由旁瓣引起的远端串扰；3）与具有相同波束成形性能的传统有源阵列进行的详尽能效比较。总体而言，我们证明所提架构在频谱效率、实施简易性（硬件复杂度）以及能效方面均具有显著优势。