The oblate spheroid as near-field scanning surface for far-field reconstruction

A nonredundant sampling representation of the field is here proposed for mapping it on a spheroidal surface that is oblate in shape and, in particular, for reconstructing it at the points fixed by an innovative near-field to far-field transformation process. The antenna under test is modelled by means of an oblate spheroid having the same rotational axis of the sampling surface, but different focal points and dimensions. In order to obtain a nonredundant sampling representation, the optimal phase function to be extracted from the field expression is evaluated, and the optimal parameters, for describing meridian ellipses and azimuthal circumferences, are determined. A fast, accurate and stable interpolation algorithm of central type is then proposed. It minimizes the truncation error for a given number of (nearest) retained samples and is stable with respect to errors affecting the data. Numerical simulations assess the effectiveness of the reconstruction process.