Reflector antennas are of paramount importance for satellite communication systems since they act as a mirror to amplify the signal power radiated from or to the Earth. When the shape of the antenna reflector is parabolic, this normally results in a narrow and symmetric antenna beam. When an antenna is designed to cover an irregularly-shaped region on Earth, the reflector is modified by raising or lowering specific areas of the parabolic surface by a few millimetres to direct the beam more accurately.
Conventional reflector antennas are generally made of rigid materials, so beams cannot be reconfigured once a spacecraft is in orbit. Phased array antennas using a large number of active elements can be reconfigured in orbit, but they have a number of disadvantages: they are rather complex; they have large mass; and they also have high power requirements, which imposes constraints on thermal management. Phased array antennas are, however, well suited when electronic beam agility is required for rapid reconfiguration of coverage.
For satellite operators, to be able to reconfigure beam coverage in-orbit would be a major breakthrough, as markets are continually evolving and customer requirements cannot be accurately predicted for the fifteen-year lifespan of today’s typical commercial telecoms satellites.
In consideration of this, ESA has supported the development of Reconfigurable Antenna Optics, or RAO. This ARTES Advanced Technology (formerly ARTES 5.1) activity encompassed the design of an antenna prototype with a reflector made from a flexible membrane whose shape can be reconfigured by means of a matrix of linear actuators. The project's prime contractor has been Thales Alenia Space France (TAS-F).
The flexible reflector is made from shell membrane bi-axial Carbon Fibre Reinforced Silicone mesh, which was extensively customized for this application by the team of Professor Horst Baier and Doctor Leri Datashvili of the Institute of Lightweight Structures, Technische Universität München (TUM-LLB), Germany, which was a project sub-contractor. TAS-F determined that this material has excellent RF reflection and passive intermodulation (PIM) free properties. That it would also maintain its flexibility for long periods in space was confirmed after an intensive test campaign in a radiation environment comparable to that encountered during the course of a satellite's lifetime.
To validate the new design, a scaled-down prototype was built and tested by TAS-F. The company says it will continue development with the goal of turning the reconfigurable antenna into a commercial product.
“Antenna systems which offer in-orbit reconfigurability is a clear need expressed by satcoms operators”, says Ludovic Schreider, Antenna Engineer, who is managing this project at TAS-F. “We think that the reconfigurable reflector developed within the framework of this ARTES Advanced Technology activity is a very promising solution. TAS-F has decided to pursue further development to increase the maturity of the technology.”
“Although further work will be required to improve reflector surface accuracy, the excellent results obtained so far by TAS-F with the support of ESA are a significant technical achievement”, says Jean-Christophe Angevain, Antenna Engineer at ESA, the project's technical officer.