On real time reflector surface distortion determination

Gain loss in large reflector antennas due to main reflector surface distortion is a significant problem in both ground and spacecraft antennas. There are several techniques under development to compensate for these distortions. However, distortions due to thermal effects are time varying and generally not known a priori. Therefore, to compensate for these distortions, it is necessary to determine the characteristics of the actual distortion in real time. Three techniques for real time measuring of the main reflector surface distortion are discussed. 1) A two-camera optical surface-measuring system using photogrammetry, 2) A small array feed placed in the focal plane of the reflector system and 3) Small probes placed on the subreflector. It was demonstrated that all three methods can recover the main reflector distortion with the subreflector probe method seeming to offer the simplest (least number of probes and minimal computation) implementation. This paper describes an experiment to verify the subreflector probe technique.