Phaseless planar near field measurements for scanned beams: difficulties, a hybrid solution and measured results

It is one of the main objectives of this paper to revisit the implementation of phaseless algorithms applicable to both non-scanned and scanned beam antennas. There are generally two techniques in the literature, interferometric and iterative methods. In general, the phase functional has a very strong nonlinear dependency on the amplitude data and the domain of optimization is typically full of local minima. This makes the functional which is going to be minimized pretty non-convex. This means that the probability of stagnation in a local minimum from a starting point is really high. Consequently, one deals with a tough optimization problem, for which the initial guess plays a critical role. In this paper we first show that the complexity of the optimization can be increased significantly whenever the AUT has a scanned beam. Second we introduce the utilization of a global optimization for finding the best initial guess to mitigate this problem. Differential evolutionary algorithm has been chosen due to its superior performances. The implementation of the method to the UCLA bi-polar near-field facility is presented as a support to the applicability of the method for scanned beams