Equivalence of Angular Stability and Reflection Locality for Metasurfaces with Anomalous Reflection

The so-called generalized reflection law defines the fields reflected from non-uniform boundaries in terms of the local reflection coefficient. Absolute majority of researchers utilize the approximation of so-called reflection locality in which the reflection coefficient at a given point (at the reference unit cell position) is assumed to be the same as if the metasurface were uniform, i.e., all the unit cells surrounding the reference one were identical. It is known that this locally periodic approximation is adequate for anomalous reflectors in case of small deviations from the usual reflection law. In this talk we will present a proof that this approximation is adequate also for strongly anomalous reflections if (and only if) the reflection coefficient of the corresponding uniform metasurfaces is independent from the incidence angle.