Full-Sphere Characterization of Low-Gain Antennas via Truncated Field Pattern Stitching

Abstract

Our work proposes a novel method for obtaining full-sphere radiation patterns from truncated measurements. This is achieved by stitching partially overlapping truncated field patterns, which together cover the whole measurement sphere. Measuring an antenna in different orientations results in a misalignment between measurements which is not perfectly known and needs to be accounted for in order to stitch the patterns together. The method first makes use of an iterative procedure to compute spherical wave coefficients (SWCs) capable of accurately describing the truncated patterns. A bounded minimization of the NMSE in the overlapping range between patterns is then done, varying through a range of translations and rotations for one pattern while keeping the other pattern fixed. After alignment, the patterns can be stitched together. The method was validated on both SWC-based and EM simulation models for randomly chosen misalignments. For all models, the NMSE after pattern stitching was found to be below −52 dB. In the final validation step, the method was tested on actual measurement results of two low-gain antennas. For each of the validation steps, potential sources of error are identified. The method demonstrates promising results in achieving full-sphere characterization of low-gain antennas in typical non-full-sphere measurement chambers.