Application of the TSWE algorithm to echo reduction of under-sampled offset spherical near-field measurements

In spherical near-field (NF) measurements, post-processing techniques based on spatial filtering have been presented as an interesting tool for the mitigation of echoes or stray signals deriving from the environment surrounding the antenna under test (AUT). The spatial filtering is very efficient in measurement scenarios with a stationary AUT. Whenever the AUT is rotating, in order to increase the effectiveness of the echo reduction, the antenna needs to be displaced outside the centre of rotation. Unfortunately, the number of acquisition samples needed to represent the AUT in offset configuration is higher with respect to one needed for the onset configuration. An innovative NF/far-field transformation algorithm for spherical offset measurements which allows to significantly reduce the number of measurement samples has been recently proposed. Such technique has been named translated spherical wave expansion (TSWE) and is based on the definition of new reference systems centred on the AUT rather than on the origin of the measurement sphere. In this study, the authors present the experimental investigation of the TSWE echo reduction properties for offset AUT.