Lens-based beam-forming antennas offer a low-power, low-cost alternative tohybrid beamforming antenna arrays. They are ideally suited to millimeter-wavemassive MIMO systems due to their native beam-space operation and angularselectivity and minimal dependence of high-speed data converters. We discussthe design of a compact and low-cost lens-based beam-forming antenna for smallform-factor platforms such as small-cells and mobile devices in 5G wirelessnetworks. We discuss a gradient-index design method and low-cost fabricationmethod based on perforated dielectrics. We discuss the need for high-contrastpermittivity ranges to achieve wide scan angles which are essential forleveraging the full capability of massive MIMO systems (e.g., full streamcapacity). Finally, we show that by using an appropriately designed perforatedmedium, gradient-index lenses with low minimum permittivity of 1.25 can achievea maximum beam-steering angle of 44 degrees. We suggest that such an approachcan enable practical low-loss, low-cost, and compact beam-steering lensantennas for millimeter-wave MIMO with wide beam-steering angles.
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