  Phased arrays, commonly used in IEEE 802.11ad and 5G radios, are capable of
focusing radio frequency signals in a specific direction or a spatial region.
Beamforming achieves such directional or spatial concentration of signals and
enables phased array-based radios to achieve high data rates. Designing beams
for millimeter wave and terahertz communication using massive phased arrays,
however, is challenging due to hardware constraints and the wide bandwidth in
these systems. For example, beams which are optimal at the center frequency may
perform poor in wideband communication systems where the radio frequencies
differ substantially from the center frequency. The poor performance in such
systems is due to differences in the optimal beamformers corresponding to
distinct radio frequencies within the wide bandwidth. Such a mismatch leads to
a misfocus effect in near field systems and the beam squint effect in far field
systems. In this paper, we investigate the misfocus effect and propose InFocus,
a low complexity technique to construct beams that are well suited for massive
wideband phased arrays. The beams are constructed using a carefully designed
frequency modulated waveform in the spatial dimension. For the special case of
beamforming along the boresight of an array, this waveform is analogous to the
frequency modulated continuous wave (FMCW) chirp signal in radar. InFocus
mitigates beam misfocus and beam squint when applied to near field and far
field systems. Simulation results indicate that InFocus enables massive
wideband phased array-based radios to achieve higher data rates than comparable
beamforming solutions.
