Effective Correction of Known 3-D Mispositioning Errors Affecting a Non-Redundant Helicoidal Near to Far-Field Transformation

In this work, an effective procedure to compensate for 3-D mispositioning errors of the probe, occurring when characterizing a long antenna through a non-redundant (NR) near to far-field (NTFF) transformation with helicoidal scan, is developed. The proposed technique involves two steps. The former allows the correction of the mispositioning errors, caused by the deviation of each sampling point from the nominal measurement cylindrical surface, using a phase correction technique called Cylindrical Wave correction. The latter restores the samples at the sampling points required by the NR representation along the scan helix from the previous ones affected by 2-D mispositioning errors, via an iterative scheme. Finally, the compensated near-field samples are effectively interpolated via an op-timal sampling interpolation (OSI) formula to accurately recover the input data required to perform the traditional cylindrical NTFF transformation. The OSI representation is here developed by assuming a long antenna under test as enclosed in a cylinder terminated by two half spheres (rounded cylinder), in order to make the representation effectively non-redundant. Numerical results, assessing the effectiveness of the proposed technique, are reported.