Short dipole as a receiver: effective aperture shapes and streamlines of the Poynting vector

The effective aperture of a receiving dipole is studied under matched and unmatched conditions. The results for the matched case correspond to expectations but lack of matching is shown to lead to quite unusual features. Analytical integration of the Poynting vector over a sphere containing the dipole shows the relative contributions of the input and reradiated fields to the total received power. The streamlines of the Poynting vector, both those ending up on the dipole and those bypassing the dipole and travelling to infinity, are determined numerically and shown in a number of figures. Vortices are shown to exist in the unmatched case. The effect of a non-uniform input wave upon the size and shape of the effective aperture is also shown. A simple experiment, likely to lead to a qualitative confirmation of the theoretical predictions, is proposed.