  We propose a novel sensing approach for the beam alignment problem in
millimeter wave systems using a single Radio Frequency (RF) chain.
Conventionally, beam alignment using a single phased array involves comparing
beamformer output power across different spatial regions. This incurs large
training overhead due to the need to perform the beam scan operation. The
proposed Synthesis of Virtual Array Manifold (SVAM) sensing methodology is
inspired from synthetic aperture radar systems and realizes a virtual array
geometry over temporal measurements. We demonstrate the benefits of SVAM using
Cram\'er-Rao bound (CRB) analysis over schemes that repeat beam pattern to
boost signal-to-noise (SNR) ratio. We also showcase versatile applicability of
the proposed SVAM sensing by incorporating it within existing beam alignment
procedures that assume perfect knowledge of the small-scale fading coefficient.
We further consider the practical scenario wherein we estimate the fading
coefficient and propose a novel beam alignment procedure based on efficient
computation of an approximate posterior density on dominant path angle. We
provide numerical experiments to study the impact of parameters involved in the
procedure. The performance of the proposed sensing and beam alignment algorithm
is empirically observed to approach the fading coefficient-perfectly known
performance, even at low SNR.
