A NF/FF transformation with spherical scan for a noncentred quasi-planar antenna using a minimum number of data

This work concerns the development of an efficient near-fleld/far-field (NF/FF) transformation with spherical scan for an offset mounted antenna under test (AUT), with a quasi-planar shape, employing a number of NF data minimum and practically equal to that for a centred mounting. Such a result has been achieved by applying the nonredundant sampling representation of electromagnetic fields to the voltage collected by the scanning probe and considering the AUT as contained in a surface formed by two circular bowls with the same aperture (double bowl). The interest for such a transformation is due to the fact that sometimes an AUT mounting centred on the scanning sphere centre cannot be possible. In such a case, the number of NF data required by the classical spherical NF/FF transformation can remarkably increase, owing to the growth of the radius of the minimum sphere containing the AUT. On the contrary, in the here considered approach, the NF data required by the standard transformation are efficiently and accurately recovered from the acquired nonredundant ones by employing a 2-D optimal sampling interpolation algorithm. This makes possible to achieve a remarkable measurement time reduction. Some numerical results assessing the accuracy and robustness of this technique are reported.