Improving the performance of the phaseless Sources Reconstruction Method for antenna diagnostics and characterization

Unmanned Aerial Vehicles (UAV)-based near field (NF) antenna measurement techniques have experienced significant development in recent years thanks to advantages like the capability of in-situ antenna testing under operational conditions. Different approaches have been proposed to tackle the associated challenges: tethered UAVs, capable of direct acquisition of complex NF measurements; indirect acquisition of the phase of the NF using an additional antenna; and iterative retrieval of the phase from the measurement of the NF amplitude at two different surfaces. While the latter is the simplest method in terms of hardware complexity, it is affected by the limitations of iterative phase retrieval methods, like stagnation due to the local minima of the cost function. This contribution explores the possibility of improving the convergence of these iterative phase retrieval methods by reducing the number of unknowns involved in the minimization problem. For this goal, the use of meshless basis functions to characterize the Antenna Under Test (AUT) is proposed. In particular, Fourier expansion and wavelets will be analyzed. An offset reflector antenna, measured at a spherical range in anechoic chamber as well as with a UAV-based antenna measurement system, will be considered for validation purposes.