Title of Presentation: Microelectromechanical Systems (MEMS) actuated Wave Front Correcting Subreflector: Distortion Compensation for Large Reflector Antennas

Primary (Corresponding) Author: William Imbriale

Organization of Primary Author: Jet Propulsion Lab

Co-Authors: Yahya Rahmat-Samii, Harish Rajagopalan, Shenheng Xu and Vahraz Jamnejad

Abstract: Gain loss in large reflector antennas due to main reflector surface distortion is a significant problem in both ground and spacecraft antennas. There are two aspects that need to be considered: 1) Since the shape of the main reflector surface is generally not known it is necessary to determine the characteristics of the actual distortion in real time and 2) A method of compensating for the distortions is required.

Three techniques for measuring 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.

Extensive work has been performed at JPL on the use of a deformable mirror to correct for the gravity induced distortions on a large ground reflector antenna. This work culminated in a demonstration of a deformable mirror on the NASA/JPL 70-meter antenna in early 1999. An electronic version of the deformable mirror is proposed for use with large reflector inflatable antennas for spacecraft. The mirror consists of a light weight surface made up of a reflect array of patches whose reflection phase is controlled via RF MEMS switches. Different reflectarray designs were studied for this particular application and it was decided that the element with variable slot on the ground plane was best suited keeping in mind the MEMS implementation. Some experimental results with the MEMS integrated with the reflect array patch are shown.