Applicability of Physical Optics for Predicting the Diffraction Pattern of Binary Metasurfaces

In this paper, we outline the domain of adequacy for the well-known approximation of physical optics (PO) for binary metasurfaces (MSs). First, we show that beyond the approximation of so-called reflection locality (RL) PO cannot be applied for practical reflecting MSs. Next, in the framework of RL approximation we derive a closed-form expression for the diffraction pattern of a finite-size binary MS and compare the results with full-wave simulations. We show that PO may be applied for a binary MS if and only if the incident and deflection angles are sufficiently small, i.e. the MS period is sufficiently large. In this case, the desired anomalous reflection is due to one of the two first-order diffraction lobes, whose magnitudes are adequately predicted by PO.