  There is today a growing need to accurately model the angular scattering
response of metasurfaces for optical analog processing applications. However,
the current metasurface modeling techniques are not well suited for such a task
since they are limited to small angular spectrum transformations, as shall be
demonstrated. The goal of this work is to overcome this limitation by improving
the modeling accuracy of these techniques and, specifically, to provide a
better description of the angular response of metasurfaces. This is achieved by
extending the current methods, which are restricted to dipolar responses and
weak spatially dispersive effects, so as to include quadrupolar responses and
higher-order spatially dispersive components. The accuracy of the newly derived
multipolar model is demonstrated by predicting the angular scattering of a
dielectric metasurface. This results in a modeling accuracy that is at least
two times better than the standard dipolar model.
