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：我们提出一种面向极高频率波段（毫米波高频段与亚太赫兹频段）的节能、实用、模块化多用户/多波束阵列馈电RIS架构。在此类频段中，信道通常在波束空间上呈现稀疏特性，且需依赖视距传输（LOS）达到可接受的接收信号强度。关键模块为有源多天线馈源（AMAF），它由少量有源天线构成，置于被动可调反射单元数量多得多的RIS近场区域。我们提出一种实用方法，以实现高增益、极低旁瓣的可控波束。通过堆叠K个此类AMAF-RIS模块，即可实现K个独立可控波束。分析中全面考虑：1）模块间的近端串扰（NEXT）；2）旁瓣导致的远端串扰（FEXT）；3）与具备相同波束赋形性能的传统有源阵列在能效上的全面对比。总体而言，该架构在频谱效率、实现简易性（硬件复杂度）和能效方面均展现出显著优势。