Modeling the field produced by a point-like dipole with an arbitrary location in the presence of a rotationally invariant nanostructure is an important issue in the context of designing nanoantennas. This is a challenging problem, as rotational symmetry is broken when introducing a noncentered dipole. Antennas larger than the wavelength are required for directivity, whereas the dipole-antenna distance is highly subwavelength, so there are two different length scales in the problem. In this paper, we introduce an original S-matrix approach based on an aperiodic-Fourier modal method. The potential of the technique is illustrated by considering three examples. We compare our results with a finite element technique.
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