  Various compositions of sparsely polarized antenna arrays are proposed in
this paper to estimate the direction-of-arrivals (DOAs) and polarizations of
multiple coherent sources. These polarized antenna arrays are composed of one
of the following five sparsely-spread sub-array geometries: 1) four
spatially-spread dipoles with three orthogonal orientations, 2) four
spatially-spread loops with three orthogonal orientations, 3) three
spatially-spread dipoles and three spatially-spread loops with orthogonal
orientations, 4) three collocated dipole-loop pairs with orthogonal
orientations, and 5) a collocated dipole-triad and a collocated loop-triad. All
the dipoles/loops/pairs/triads in each sub-array can also be sparsely spaced
with the inter-antenna spacing far larger than a half-wavelength. Only one
dimensional spatial-smoothing is used in the proposed algorithm to derive the
two-dimensional DOAs and polarizations of multiple cross-correlated signals.
From the simulation results, the sparse array composed of dipole-triads and
loop-triads is recommended to construct a large aperture array, while the
sparse arrays composed of only dipoles or only loops are recommended to
efficiently reduce the mutual coupling across the antennas. Practical
applications include distributed arrays and passive radar systems.
