Large Imaging Reflectarray in Ka band – GRAIK

The project has for target to demonstrate the feasibility of an antenna with a large number of beams in Ka band, for the civil and military telecommunications. This need is clearly identified for the multimedia systems, in the objective to increase their capacity. A multispot antenna affords a better robustness to jamming on the theatres of operations, and is thus very attractive for the military telecommunications.

Very directive spots are achieved with a very big antenna aperture. The reflector maximal diameter in Europe is 2.4*3,6 m2. A solution with a foldable reflectarray antenna is being developed in Thales Alenia Space. It is envisaged at the moment only for the low frequency bands (L, S, C). This antenna is ideal for the sizes included between 4m and 8m. It is an alternative solution of the big American Mesh reflectors, while requiring much lower development costs.

The rise in frequency of the big radiating apertures induces manufacturing accuracy and thermo-elastics issues, which affect the quality of the beams.

The disruptive concept proposed here consists in using this big radiating aperture in a new configuration, an Imaging Array. The Imaging Array is made of two confocal reflectors, one very big, the other smaller. This optical subsystem magnifies a primary phased array. With such an architecture, it becomes possible to clear for the effects of the static and dynamic deformations by means of phase shifters placed at the level of the focal array. The demonstration of this feasibility constitutes the first objective of this project. It will be applied to the particular case of a large reflectarray.

The second critical point of such an antenna subsystem lies in the Beam Forming Network (BFN). An innovative approach, free of anteriority in intellectual property, is developed at the Institute of Electronics and Telecommunications of Rennes ( IETR). It concerns a BFN referred to as a "Pill-Box". We suggest performing in this project the first demonstration of such a Pillbox BFN in two dimensions. The concept is moreover original and a joint patent registration IETR / TAS is currently being developed.

This experimental demonstration, associated with the optimal dimensioning of the architecture antenna, and in the demonstration of the possibility of clearing for the shape imperfections of a large reflectarray will show the feasibility of such an antenna subsystem.

This project will allow to remove both critical points identified for such an antenna. It will open considerable perspectives because the aimed product corresponds to a priority need for telecommunications civil and military operators.