  Traditional point-to-point line-of-sight channels have rank 1, irrespective
of the number of antennas and array geometries, due to far-field propagation
conditions. By contrast, recent papers in the holographic multiple-input
multiple-output (MIMO) literature characterize the maximum channel rank that
can be achieved between two continuous array apertures, which is much larger
than 1 under near-field propagation conditions. In this paper, we maximize the
channel capacity between two dual-polarized uniform rectangular arrays (URAs)
with discrete antenna elements for a given propagation distance. In particular,
we derive the antenna spacings that lead to an ideal MIMO channel where all
singular values are as similar as possible. We utilize this analytic result to
find the two array geometries that respectively minimize the aperture area and
the aperture length.
