  Metasurfaces offer great potential to control near- and far-fields through
engineering of optical properties of elementary cells or meta-atoms. Such
perspective opens a route to efficient manipulation of the optical signals both
at nanoscale and in photonics applications. In this paper we show that by using
an effective surface conductivity tensor it is possible to unambigiously
describe optical properties of an anisotropic metasurface in the far- and
near-field regimes. We begin with retrieving the effective surface conductivity
tensor from the comparative analysis of experimental and numerical reflectance
spectra of a metasurface composed of elliptical gold nanoparticles. Afterwards
restored conductivities are validated in the crosscheck versus semianalytic
parameters obtained with the discrete dipole model with and without dipoles
interaction contribution. The obtained effective parameters are further used
for the dispersion analysis of surface plasmons localized at the metasurface.
The effective medium model predicts existence of both TE- and TM-polarized
plasmons in a wide range of optical frequencies and describes peculiarities of
their dispersion, in particularly, topological transition from the elliptical
to hyperbolic regime with eligible accuracy. The analysis in question offers a
simple practical way to describe properties of metasurfaces including ones in
the near-field zone by extracting effective parameters from the convenient
far-field characterisation.
