Near-Field Far-Field Transformations with Unknown Probe Antennas

The characterization of unknown antennas under test (AUTs) from measurements of the radiated near field (NF) is commonly performed with known probe antennas. By accounting for the behavior of a given probe in the processing of the NF data, the obtained quantities of interest, e.g., the far-field (FF) behavior of the radiator, are free of biases and distortions caused by the probe sensor. We discuss an NF FF transformation (NFFFT) which can fully compensate the effect of the probe, while only requiring knowledge about its electrical size, position, and orientation. An iterative nonconvex technique based on alternating projections is discussed, as well as a convex approach utilizing bilinear forms is provided. Connections to the related problem of phase retrieval are highlighted. Simulation results showcase the validity of NFFFTs with full probe correction of unknown probes and shed some light on potential limitations.