  In this letter, we consider transceivers with spatially-constrained antenna
apertures of rectangular symmetry, and aim to improve of spatial degrees of
freedom (DoF) and channel capacity leveraging evanescent waves for information
transmission in near-field scenarios based on the Fourier plane-wave series
expansion. The treatment is limited to an isotropic scattering environment but
can be extended to the non-isotropic case through the linear-system theoretic
interpretation of plane-wave propagation. Numerical results show that
evanescent waves have the significant potential to provide additional DoF and
capacity in the near-field region.
