On the Use of Probe Signal Derivatives in Spherical Near-Field Antenna Measurements

Sampling of the probe signal first-order spatial derivative, in addition to the probe signal itself, enables the sampling step to be increased to twice that of the standard sampling criterion. In this work, we investigate - theoretically, numerically, and experimentally - the potential of using probe signal derivatives for spherical near-field antenna measurements with the aim of reducing the measurement time. We present a closed-form Fourier coefficient formula and a closed-form interpolation formula based on signal and signal derivative samples. We validate these new formulas using experimental measurement data and thus demonstrate the feasibility of doubling the sampling step in practice. We discuss different principles for determining the probe signal derivative; and we demonstrate the use of probe signal derivatives, in addition to probe signals themselves, for a full-sphere near-field antenna measurement skipping every second full-circle scan.