Spectral-impulse-response approach for analyzing the aperiodic excitation of a periodic diffraction grating

We present an analytical method to solve the problem of the aperiodic excitation of a periodic diffraction grating. In the case of a metallic grating, expressions are derived for the scattered field due to a point source excitation, thus determining the corresponding aperiodic Green´s function for both field polarizations. Plane-wave decomposition, spectral techniques, and the introduction of a Spectral Impulse Response (SIR) are used to determine the scattered field. This SIR based solution is accurate even when the grating is in the near-field of a source, and can identify the diffracted space harmonics of complex scattering phenomena, while remaining applicable for arbitrary excitations. The theoretical model is validated against a full-wave field simulator, and is shown to be accurate at different field regions.