A wavefront-correction system has been proposed as part of an outer-space radio communication system that would include a large, somewhat flexible main reflector antenna, a smaller subreflector antenna, and a small array feed at the focal plane of these two reflector antennas. Part of the wave-front-correction system would reside in the subreflector, which would be a planar patch-element reflectarray antenna in which the phase shifts of the patch antenna elements would be controlled via microelectromechanical systems (MEMS) radio-frequency (RF) switches. The system would include the following sensing-and-computing subsystems:
- An optical photogrammetric subsystem built around two cameras would estimate geometric distortions of the main reflector;
- A second subsystem would estimate wavefront distortions from amplitudes and phases of signals received by the array feed elements; and
- A third subsystem, built around small probes on the subreflector plane, would estimate wavefront distortions from differences among phases of signals received by the probes.
The distortion estimates from the three subsystems would be processed to generate control signals to be fed to the MEMS RF switches to correct for the distortions, thereby enabling collimation and aiming of the received or transmitted radio beam to the required precision.
This work was done by William A. Imbriale and Vahraz Jamnejad of Caltech and Yahya Rahmat-Samii, Harish Rajagopalan, and Shenheng Xu of the University of California, Los Angeles, for NASA’s Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Electronics/Computers category. NPO-46053
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Wavefront Correction for Large, Flexible Antenna Reflector
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Overview
The document titled "Wavefront Correction for Large, Flexible Antenna Reflector" from NASA's Jet Propulsion Laboratory (JPL) discusses advancements in correcting surface distortions in large reflector antennas used in space applications. Over the past decade, JPL has focused on using a mechanically Deformable Flat Plate (DFP) to mitigate gravity-induced distortions in large antennas, such as the 70-meter antenna of the Deep Space Network (DSN). The DFP is designed to be deformed in real-time to compensate for distortions as the antenna moves, improving gain by over 3 dB at lower elevation angles.
However, applying this technology to spacecraft antennas presents challenges, primarily due to the unknown shape of the main reflector surface and the excessive weight of the DFP system. To address these issues, the document proposes a MEMS (Microelectromechanical Systems) actuated Wave Front Correcting Subreflector. This innovative subreflector, used in conjunction with an array feed, aims to correct for both pointing errors and gain loss caused by distortions in real-time. The subreflector features a lightweight design with a reflect array of patches controlled by RF MEMS switches, allowing for variable phase shifts to achieve wavefront correction.
The document outlines three techniques for real-time measurement of surface distortions: an optical surface-measuring system using photogrammetry, a small array feed placed in the focal plane of the dual reflector system, and small probes on the subreflector to measure relative phase differences. These methods aim to provide accurate and timely data on reflector distortions, which is critical for maintaining antenna performance.
The overarching goal of this research is to demonstrate essential components for a complete antenna system, minimizing risks for future developments. The document emphasizes the need for larger apertures in spaceborne antenna systems to enhance performance across various frequency regimes. It also discusses the advantages of inflatable antennas, which offer significant benefits in mass and packaging volume, while highlighting the potential of MEMS technology to extend operational frequency and size limits.
In summary, the document presents a comprehensive approach to addressing the challenges of surface distortion in large, flexible antennas, showcasing innovative solutions that leverage MEMS technology for improved performance in space communications.
