  The requirement of high data-rate in the fifth generation wireless systems
(5G) calls for the ultimate utilization of the wide bandwidth in the mmWave
frequency band. Researchers seeking to compensate for mmWave's high path loss
and to achieve both gain and directivity have proposed that mmWave
multiple-input multiple-output (MIMO) systems make use of beamforming systems.
Hybrid beamforming in mmWave demonstrates promising performance in achieving
high gain and directivity by using phase shifters at the analog processing
block. What remains a problem, however, is the actual implementation of mmWave
beamforming systems; to fabricate such a system is costly and complex. With the
aim of reducing such cost and complexity, this article presents actual
prototypes of the lens antenna as an effective device to be used in the future
5G mmWave hybrid beamforming systems. Using a lens as a passive phase shifter
enables beamforming without the heavy network of active phase shifters, while
gain and directivity are achieved by the energy-focusing property of the lens.
Proposed in this article are two types of lens antennas, one for static and the
other for mobile usage. Their performance is evaluated using measurements and
simulation data along with link-level analysis via a software defined radio
(SDR) platform. Results show the promising potential of the lens antenna for
its high gain and directivity, and its improved beam-switching feasibility
compared to when a lens is not used. System-level evaluations reveal the
significant throughput enhancement in both real indoor and outdoor
environments. Moreover, the lens antenna's design issues are also discussed by
evaluating different lens sizes.
