Photogrammetric measurement of the gravity deformation in a Cassegrain antenna

Photogrammetric measurement of the gravity deformation in a 22-m Cassegrain antenna of the Australia Telescope Compact Array is described. The deformation in the main reflector surface and displacements of the quadripod structure, subreflector, and feed were surveyed at a set of antenna elevations. The elevation dependance of the antenna radiation pattern, calculated from the deformations and displacements, are in good agreement with measurements. This experience is another novel demonstration of the usefulness of photogrammetry in antenna metrology: as a tool for measurements of the gravity-induced structural deformation in reflector surfaces and of the displacements and rotations in optics elements of large steerable antennas.