Under-Sampled Spherical Near-Field Antenna Measurements With Error Estimation

This article proposes an under-sampling scheme in φ for spherical near-field antenna measurements. Reducing the number of samples along one of the spherical coordinates allows to decrease the number of positioner steps. Therefore, the savings in the number of samples are almost directly translated into measurement time savings. Under-sampling usually leads to aliasing; however, it can be controlled by exploiting the properties of the spherical wave expansion. The axial symmetry of conventional antennas leads to narrow azimuthal spectra, where the influence of this aliasing is small. By designing an estimator of the error introduced by the aliasing, the required number of φ samples for a given accuracy can be determined, without any
a priori
knowledge about the antenna under test. This allows the application of this technique for any kind of antenna regardless of its level of axial symmetry, obtaining different values of measurement time savings depending on the level of symmetry. Several examples using the numerical and measured data are presented, showing significant reductions in the measured samples for different antennas. In addition, the algorithm is successfully tested against antennas with poor axial symmetry to demonstrate its robustness.