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

Classical  probe  corrected  Spherical  Near  Field (SNF)  measurement  assumes  a  |μ|  =  1  probe.  This requirement  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 MVI SP1100 probe is investigated using MV-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.