Antenna reflector metrology: the Australia Telescope experience

A description is given of some refinements to the traditional theodolite and tape technique for surveying the reflector surface of large antennas. The theodolite is positioned in the structural axis about 40 cm above the antenna vertex. There are six rings of panels, ranging in size from 1.4 m×0.7 m to 2 m×2 m, with 160 panels in all in each antenna. Targets are placed near the corners of each panel. In brief, each target´s position is defined by two measurements: its distance from the theodolite, and the angle between the antenna axis and the line of sight to target, the zenith angle. The equipment and the procedures used are reported. The authors examine the accuracy achieved in each measurement and discuss the consequent panel positional accuracy. In applications (to radio telescope antennas 18-m and 22-m in diameter), surface accuracies of 0.25 mm root mean square (RMS) have been achieved