Probe-Corrected Near-Field to Far-Field Transformation Using Multiple Spherical Wave Expansions

Near-field to far-field transformations constitute a powerful antenna characterization technique for near-field measurement scenarios. In this paper a near-field to far-field transformation technique based on multiple spherical wave expansions is presented. Thanks to its iterative matrix inversion nature, the approach performs the transformation of fields measured on arbitrary surfaces. Also, irregular sampling schemes can be incorporated. The proposed algorithm is based on modelling the antenna fields with not one, but several spherical wave expansions distributed over its geometry. Due to the high number of spherical wave expansions, their truncation number can be arbitrarily reduced. Working with expansions of low order allows to incorporate the probe correction in the transformation in a very simple way, accepting any type of probe and orientation. Only the probe far-field pattern is used, thus working with its full spherical wave expansion is avoided. The algorithm is validated using simulated field data as well as measurements of real antennas.