Scattering from finite periodic structures on an infinite dielectric slab is relevant to a variety of engineering applications. Recent studies have demonstrated the effectiveness and physical insight gained when describing the scattering phenomena in terms of truncated Floquet waves (FW) and Floquet-modulated wave types. The array Green's function of a finite array may be represented collectively as the radiation from a superposition of continuous truncated FW (TFW) distributions on the aperture of the array. Since the FW series exhibits excellent convergence properties when the observation point is far away from the array surface, the TFW representation is found more efficient than the direct summation of the spatial contributions from each element of the array, especially when each FW aperture distribution is treated asymptotically. In this paper, we explore the high-frequency diffraction phenomena from a finite array of electric line sources on a truncated dielectric slab. The FW-diffracted rays and the excitation of guided waves at the array truncation are described. The effects of the slab truncation are introduced using a physical optics (PO) approximation for both the volumetric polarization currents and the ground plane surface currents. Furthermore, the diffraction mechanisms at a slab truncation of all wave types excited at the array edge are discussed. In order to validate the asymptotic formulation a full wave solution of the problem has been developed by solving an appropriate integral equation with the method of moments (MoM).
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