Phaseless Near-Field Far-Field Transformation Utilizing Combinations of Probe Signals

Phaseless near-field far-field transformations based on nonconvex optimization suffer from local stationary points. In order to avoid the corresponding suboptimal solutions, the incorporation of combinations of probe signals into the cost functional is proposed and investigated. The nonconvex optimization based on the Wirtinger Calculus relies on forward and adjoint radiation operator evaluations via the fast irregular antenna field transformation algorithm (FIAFTA) and is performed by a memory-limited Quasi-Newton method. This allows the solution of large scale problems with utilization of the full flexibility of the FIAFTA in terms of measurement probe correction and arbitrary sample locations. Results for synthetic and measured near-field data reveal significant improvements when the knowledge of probe signal combinations is utilized, especially in applications with a large number of unknowns.