<p>Some innovative near-field antenna measurement setups, e.g., UAV-based, have limited capabilites for providing a phase and magnitude reference to the receiver. Phaseless antenna measurements have always been an important topic for such scenarios, but they often suffer from the unreliability of nonconvex phase retrieval algorithms, necessity of extremely accurate magnitude measurements and strong oversampling requirements. A similar problem arises if the measured magnitudes are impaired, i.e., if the global magnitude reference is unreliable for instance due to drift. We present a linearized method to reconstruct the phases for measurements without a global phase reference as well as an inherently linear method to reconstruct the magnitudes for measurements without a global magnitude reference. The underlying assumption is that a drift in either the phase or the magnitude occurs during the field measurement. With the reconstructed, thus, fully consistent observation vector, standard electromagnetic field transformations are possible and yield accurate and reliable results.</p>

<p>Reducing near-field measurement times is an important challenge for future antenna measurement systems. We propose to incorporate knowledge about material parameters of the antenna measurement environment within the simulation model. To do so, a method-of-moments code with surface discretization is implemented as a side constraint to the near-field far-field transformation problem performed with the fast irregular antenna field transformation algorithm. Transformation and source reconstruction results of synthetic measurement data demonstrate the effectiveness of the proposed method.</p>

<p>Phase retrieval, in particular for the operators arising from near-field measurements, is a non-convex task suffering from a severe lack of reliability due to local minima and false solutions. Approaches to tackle this issue, in turn, suffer from strict and often unrealistic oversampling requirements and possibly unfeasible computational complexities—in particular when larger scenarios are considered. In this paper, we analyze the sampling requirements for convex phase retrieval based on partially coherent observations which are captured with multi-probe arrays. We discuss requirements for the orientation and positioning of the probe antennas in the probe arrays. Following these conditions, a recently introduced linearized method is able to reconstruct a unique global solution reliably. The theoretical deliberations are corroborated with simulated near-field data.</p>

<p>Conventional phaseless near-field measurement data is not adequate for reliable transformation into the far field. We tackle this challenge by a formulation working with multifrequency phaseless measurements under the assumption of coherently measured spectra. Such data is, for instance, obtained with a transmitting antenna under test and standard receivers featuring a nonzero coherent bandwidth. The focus of this work is on an advanced algorithm to demonstrate that this ansatz is very promising for further research and real-world investigations. Empirical studies based on simulation data demonstrate that appropriately merging this multi-frequency data significantly increases the chance of successful phaseless near-field far-field transformation. As a by-product, this multi-frequency phase retrieval method supports also the retrieval of the phase of farfield antenna measurements.</p>

<p>Phase retrieval, in particular for the operators arising from near-field measurements, is a non-convex task suffering from a severe lack of reliability due to local minima and false solutions. Approaches to tackle this issue, in turn, suffer from strict and often unrealistic oversampling requirements and possibly unfeasible computational complexities—in particular when larger scenarios are considered. In this paper, we analyze the sampling requirements for convex phase retrieval based on partially coherent observations which are captured with multi-probe arrays. We discuss requirements for the orientation and positioning of the probe antennas in the probe arrays. Following these conditions, a recently introduced linearized method is able to reconstruct a unique global solution reliably. The theoretical deliberations are corroborated with simulated near-field data.</p>