Phase Retrieval for Spherical Near-Field Measurements using Two Antenna Positions

The Two Scans phase retrieval technique is based on magnitude measurements of the antenna under test (AUT) in two different configurations and the analytical relation between these two measurements. For spherical near-field measurements this relation is given by the spherical transmission formula and the best-known implementation of this method makes use of nearfield measurements over two measurement spheres. In this paper we propose a novel method where the two sets of near-field measurements are measured over a single sphere, with the AUT in two different positions wrt. the origin of the measurement coordinate system. The two positions are known in the measurement coordination system, and the relationship between the AUT transmission coefficients for the two positions is given by the transmission formula, or by a far-field phase translation. The phase is then retrieved through an iterative process between the two measurements. The principles of this approach will be presented and the performance will be evaluated based on simulated data. Particularly, the impact of the extent of the translation on the accuracy of the phase retrieval will be studied, and the viability of the method for real applications will be discussed. Additionally, the possibilities of an error metric in the complex domain is explored by performing two simultaneous retrievals, starting from two different initial phase guesses, and tracking the complex difference between the two to determine whether the algorithm has converged correctly.