  While metasurfaces (MSs) are constructed from deeply-subwavelength unit
cells, they are generally electrically large and full-wave simulations of the
complete structure are computationally expensive. Thus, to reduce this high
computational cost, non-uniform MSs can be modelled as zero-thickness
boundaries, with sheets of electric and magnetic polarizations related to the
fields by surface susceptibilities and the generalized sheet transition
conditions (GSTCs). While these two-sided boundary conditions have been
extensively studied for single sheets of resonant particles, it has not been
shown if they can correctly model structures where the two sides are
electrically isolated, such as a fully-reflective surface. In particular, we
consider in this work whether the fields scattered from a fully reflective
metasurface can be correctly predicted for arbitrary field illuminations, with
the source placed on either side of the surface. In the process, we also show
the mapping of a PEC sheet with a dielectric cover layer to bi-anisotropic
susceptibilities. Finally, we demonstrate the use of the susceptibilities as
compact models for use in various simulation techniques, with an illustrative
example of a parabolic reflector, for which the scattered fields are correctly
computed using a integral equation (IE) based solver.
