We propose a spatial multiplexing system using reconfigurable cavity-backed metasurface antennas. The metasurface antennas consist of a printed cavity with dynamically tunable metamaterial radiators patterned on one side and fed by multiple radio frequency ports on the other side (each port representing one communication node), forming a shared aperture. By individual tuning of the radiators, the antennas can generate steerable, concurrent beams that can be adapted to the properties of multiple-input-multiple-output (MIMO) channels. In this paper, we present a 2 x 2 MIMO system with simulated metasurface antennas as transmit and receive antennas operating at 5.9 GHz. We demonstrate that the flexibility in beamforming supported by the metasurface antennas can be used to achieve low spatial correlation and high SNR gain in clustered MIMO channels, leading to a significant improvement of the channel capacity. Numerical studies show 2.36-fold, 2.11-fold enhancements of capacity in MIMO channels with one and two clusters, respectively, compared with an MIMO system consisting of linear dipoles. The MIMO system based on the metasurface antennas can be low cost, low profile, and low power. The metasurface antenna thus has potential applications in small cell networks requiring high data rate under bandwidth, energy, and cost constraints.
