Near-Field / Far-Field Application for a Spherical Scanner at mm-Wave Frequencies

This paper describes a measurement system designed and built for measuring radiation patterns of stationary antennas at mm-Wave frequencies. The mechanical design of the system's positioner fixes the radial test distance; implying that the system can be used as either a spherical near field or far-field test system depending on the electrical size and mounting location of the radiator. For implementation of the former, our use of a spherical wave modal expansion requires the creation of a spherical surface with known sampling grid and any deviation introduces uncertainty. We show in this paper to what extent the mechanical positioner approximates an ideal spherical surface and how active angular correction of the rotary positioners allow us to correct for gravitational deformation.