A Nonredundant Sampling Representation Managing an Offset Mounting of an Elongated Antenna in a Spherical Near-Field Facility

An efficient spherical near-field-to-far-field transformation (NFTFFT), which takes into account the offset mounting of an elongated antenna and employs the same nonredundant (NR) amount of near-field (NF) data as in the onset mounting case, is presented. The interest for this NFTFFT is due to the fact that, for practical reasons, a mounting where the antenna and the scan sphere centers coincide is not always possible. In this case, the amount of NF measurements required by the traditional spherical NFTFFT can significantly increase. In the developed NFTFFT, this drawback has been overcome by accurately recovering these NF data from the gathered NR probe voltage samples through a sampling expansion, attained by suitably using the NR sampling representations and assuming the antenna as enclosed in a prolate spheroid. Numerical and experimental results are reported in order to assess the efficacy of the developed technique.