  The majority of stochastic channel models rely on the electromagnetic
far-field assumption. This assumption breaks down in future applications that
push towards the electromagnetic near-field region such as those where the use
of very large antenna arrays is envisioned. Motivated by this consideration, we
show how physical principles can be used to derive a channel model that is also
valid in the electromagnetic near-field. We show that wave propagation through
a three-dimensional scattered medium can be generally modeled as a linear and
space-variant system. We first review the physics principles that lead to a
closed-form deterministic angular representation of the channel response. This
serves as a basis for deriving a stochastic representation of the channel in
terms of statistically independent Gaussian random coefficients for randomly
spatially-stationary propagation environments. The very desirable property of
spatial stationarity can always be retained by excluding reactive propagation
mechanisms confined in the extreme near-field propagation region. Remarkably,
the provided stochastic representation is directly connected to the Fourier
spectral representation of a general spatially-stationary random field.
