  In this article, we discuss the potential of radio frequency (RF) lens for
ultra-wideband millimeter-wave (mmWave) systems. In terms of the beam squint,
we compare the proposed RF lens antenna with the phase shifter-based array for
hybrid beamforming. To reduce the complexities for fully digital beamforming,
researchers have come up with RF lens-based hybrid beamforming. The use of
mmWave systems, however, causes an increase in bandwidth, which gives rise to
the beam squint phenomenon. We first find the causative factors for beam squint
in the dielectric RF lens antenna. Based on the beamforming gain at each
frequency, we verify that, in a specific situation, RF lens can be free of the
beam squint effect. We use 3D electromagnetic analysis software to numerically
interpret the beam squint of each antenna type. Based on the results, we
present the degraded spectral efficiency by system-level simulations with 3D
indoor ray tracing. Finally, to verify our analysis, we fabricate an actual RF
lens antenna and demonstrate the real performance using a mmWave, NI PXIe,
software-defined radio system.
