Optimization of the near-field spherical spiral scanning for the radiation pattern reconstruction of an offset quasi-planar antenna

An optimization of the near-field data acquisition on a spherical spiral for recovering the radiation pattern of a quasi-planar antenna, which is non-centred with respect to the scanning system, is here presented. As a matter of fact, such an unusual antenna positioning reflects negatively on the number of the needed near-field data, since this last depends on the smallest spherical surface enclosing the antenna under test and sharing the same centre as the scanning surface. The proposed optimization reduces such a number through a non-redundant sampling representation of the measured voltage adopting a suitable source modelling. The so collected samples are then employed in a two-dimensional optimal sampling interpolation algorithm for retrieving the near-field data indispensable to carry out the classical near-field to far-field transformation. Numerical and experimental tests endorse the effectiveness of the proposed method.