Toward Nonlocal Programmable Metasurfaces for Multiuser Orthogonal Beamforming

Abstract

A circuit-based metasurface is proposed for multiuser orthogonal beamforming and multiple-input-multiple-output (MIMO) wireless communications. The metasurface consists of several pairs of propagation and phased shifter layers, stacked several times to form an electrically thin structure that provides the necessary nonlocality and programmability for electronic beamforming of multiple users/streams. The propagation layers consist of low-profile redistribution layers (RDLs) and allow the lateral propagation of waves, thus enabling nonlocality. The phase-shifter (training) layers introduce controllable phase delays to the propagating signals, thereby enabling the reconfigurability of the metasurface. The orthogonality of the beamforming is analyzed based on the proposed metasurface topology, with two beams optimized for a $\mathbf{2 0} \times \mathbf{2 0}$-element metasurface designed for satellite communications in the millimeter wave frequency bands.