Uncertainties Introduced by the Probe in Millimeter-Wave Planar Near-Field Measurements

No measurement is complete without a thorough investigation of the involved uncertainties. This paper investigates uncertainties introduced by the probe in planar near-field measurements at the mm-wave frequencies 90 GHz and 140 GHz. This includes probe compensation and multiple reflections between the probe and the antenna-under-test. A combination of simulations and measurements is used to achieve an as accurate as possible estimation of each uncertainty. Manufacturing uncertainties in the probe as well as the placement of electromagnetic absorbers on the probe flange, show a significant influence on the transformed planar near-field radiation patterns. When using an open-ended rectangular waveguide as a probe, manufacturing errors can reduce the trueness of the probe pattern and resulting far-field pattern of the antenna-under-test to below 90% for θ > 17° (90 GHz) or θ > 22° (140 GHz). The presence of electromagnetic absorbers on the flange can cause the precision to drop below ±0.25 dB at broadside. Therefore, both these effects should be modelled beforehand to obtain an accurate radiation pattern of the antenna-under-test.