  Apart from the conventional parameters (such as signal-to-noise ratio, array
geometry and size, sample size), several other factors (e.g. alignment of the
antenna elements, polarization parameters) influence the performance of
direction of arrival (DOA) estimating algorithms. When all the antenna elements
are identically aligned, the polarization parameters do not affect the steering
vectors, which is the underlying assumption of all the conventional DOA
algorithms. Unfortunately, in this case, for a given set of DOA angles there
exists a range of polarization parameters which could result in a very low
signal-to-noise ratio (SNR) across all the antenna elements in the array. To
avoid this type of catastrophic event, different antenna element needs to be
aligned differently. However, this fact will make almost all commonly used DOA
estimation algorithms non-operable, since the steering vectors are contaminated
by the polarization parameters. To the best of our knowledge, no work in the
literature addresses this issue even for a single user environment. In this
paper, that line of inquiry is pursued. We consider a circular array with the
minimum number of antenna elements and propose an antenna alignment scheme to
ensure that at any given point no more than one element will suffer from
significantly low SNR due to the contribution of polarization. A low complexity
algorithm that estimates the DOA angles in a closed-form manner is developed.
We treat MUSIC as the baseline algorithm and demonstrate how it can reliably
operate in all possible DOA and polarization environments. Finally, a thorough
performance and complexity analysis are illustrated for the above two
algorithms.
