Improving the accuracy of numerical results by a spherical-multipole based post-processing

Spherical-multipole analysis is applied to improve the far-field results obtained from numerically computed near-field data. This is done by means of a spatial-frequency filtering technique, since the spatial spectral-radius of the exact problem is limited and depends only on the maximal electric distance of the sources to the well-chosen origin. Neglecting the higher spectral parts, i.e. the higher-order multipole amplitudes in the far-field representation, means neglecting spurious and erroneous field parts. The method is applicable for frequency-domain methods as well as for time-domain fields, provided that the time spectrum band of the field is known. Exemplarily, we apply the spatial-frequency filtering technique while performing a spherical-multipole based time-domain near-to-far-field transform for the finite-difference time-domain (FDTD) method. In the example, we consider scattering by a perfectly electrically conducting (PEC) half-sphere illuminated by a Gaussian-type modulated plane electromagnetic wave.