Differential Phase Measurement Method for Determining Scanner Planarity at Submillimeter Wavelengths

At submillimeter wavelengths, planarity error of the near- field scanner may be considerable, and therefore, needs to be eliminated when high phase measurement accuracy is desired. In this paper, we consider a differential phase measurement method, where the scanner planarity profile is determined from the submillimeter-wave phase data, and thus, no specific planarity measurements with a tracking laser interferometer are needed. A similar method has been used earlier in high- accuracy profile measurements of machined surfaces. We show in this paper some simulation and measurement results. By simulations we study, e.g., how sensitive the differential phase measurement method is to measurement errors. By measurements done with a planar scanner and a millimeter-wave vector network analyzer we show how this method works at 310 GHz and 650 GHz.