Freehand System for Probe-Fed Antenna Diagnostics by Means of Amplitude-Only Acquisitions

This article presents a system for easing the characterization of probe-fed antennas on available probe stations. Many of these stations were deployed for scattering parameter measurement but not for radiation pattern acquisition. Furthermore, these latter acquisitions have traditionally required the use of mechanical positioners for the automated movement of the probe antenna along different surfaces. Integration of these mechanical systems can be complex in some probe stations due to physical constraints. This work proposes an easy-to-deploy freehand system for amplitude-only field acquisitions providing great flexibility for probe-fed antenna diagnostics. In addition, the use of feeding probes, which can be bulky if compared to low-gain antennas is known to result in partial blocking avoiding the acquisition of the radiation pattern for some angles and for causing reflections yielding some ripple and distortion in the measured pattern. The system benefits from a near-field (NF) to far-field (FF) transformation based on the source reconstruction method so that unwanted reflections can be spatially identified and filtered out. Finally, broadband phaseless acquisition based on interferometry is implemented. This technique enables to alleviate the requirements of a full-vector (i.e., amplitude and phase) acquisition without losing information regarding the time-domain behavior and to retrieve all the frequencies simultaneously without losing the coherence between them so that parameters such as the delay spread can be measured. Simulated and experimental results in the V-band from 57 to 66 GHz are analyzed to validate the proposed system. Results are in fair agreement with both simulations and a direct FF acquisition on a conventional automated spherical system used as a reference.