Complete Analysis of Spherical Higher Order Mode Excitation in Antenna Measurement Probes



Classical probe corrected Spherical Near Field (SNF) measurement assumes a |μ| = 1 probe.

This requirements is needed to fully compensate the effect of the probe during the NF/FF transformation. If the probe has an higher order mode content, a residual error will affect the measured pattern (probe modal truncation). This requirement leads to challenging probe designs especially if the required bandwidth is wide and/or there is a limitation on the acceptable dimension. As a consequence, in many practical cases, higher order spherical modes could be radiated. In this paper, the source of higher order spherical modes of the MVG SP1100 probe is investigated using INSIGHT software which reconstructs equivalent currents starting from the measured NF. The equivalent currents associated to higher order modes have been computed on a conformal geometry encompassing the probe. In this way, the origin of such higher order modes has been deduced.