Using a Tracking Laser Interferometer to Characterize the Planarity of a Planar Near-Field Scanner
Authors: Paul R. Rousseau, William C. Wysock, Carlos M. Turano, John R. Proctor
This paper describes the experience of using a tracking laser interferometer to align and characterize the planarity of a planar near-field scanner. Last year, The Aerospace Corporation moved their planar near-field antenna range into a new larger room with improved environmental controls. After this move, the near-field scanner required careful alignment and characterization. The quality of the scanner is judged by how accurately the probe scans over a planar surface. The initial effort to align the scanner used a large granite block as a planarity reference surface and cumbersome mechanical probe measurements. However, a tracking laser interferometer was used for the final alignment and characterization.
The laser interferometer was included as part of an alignment service purchased from MI Technologies. The tracking laser interferometer emits a laser beam to a mirrored target called an SMR (Spherically Mounted Retroreflector). Encoders in the tracker measure the horizontal and vertical angles while the laser interferometer measures the distance. From these measurements, the three-dimensional SMR location is determined. The laser has the ability to very accurately (within about 0.001 inch) measure the location of the scanning near-field probe.
This paper includes a description of the mechanical alignment of the scanner, the tracking laser interferometer measurements, and the final planarity characterization.