|Start:||01 September 2009|
|End:||31 March 2011|
|Department:||Statistical Inference (SI)|
Most commercial communication satellites today have a 15 to 18 years lifetime in orbit. This means that by adding the duration of the system definition study, the coverage of the satellite antenna must be frozen around 20 years before the end of the mission. It is obvious that during such a long period the traffic demand, e.g. multimedia, TV broadcast or phone, evolve drastically.
Therefore, a very attractive solution for satellite operators is to have an antenna that is able to change its coverage in flight. The extra cost that is involved in such a solution should be reasonable. For this reason, it is proposed in this study to perform the coverage re-configurability for lateral side antennas by modifying the sub-reflector characteristics while keeping the lightweight main reflector technology unchanged. In case earth-deck antennas are considered, then reflect-array can be implemented either on sub or main reflector. A note here is that up to now linear polarisation has received more attention for reflect-arrays than circular polarisation. However, the trend of using more and more circular polarisation in space telecommunication systems also asks for an increased effort in the development of circular polarised reflect-array antennas.
To achieve the re-configurability, this study will perform the design and development of a RF-MEMS controlled reflect-array. One of the critical issues of using MEMS switches is the reliability and the power handling, but it is foreseen that for the typical applications referred to in this activity the power per MEMS element will not exceed 1 to 2 W and that graceful degradation is available from the design. Final performances will have to be demonstrated by test with a partial reflect-array demonstrator and analyses at antenna level. The reflect-array demonstrator shall be electrically representative and compliant with the requirements and make use of active non-frozen RF-MEMS switches. The development focus shall be on reflect-array architecture, concepts and technologies to obtain low cost solutions for the overall antenna. The reflect-array design shall also be versatile to allow incorporating the most suitable RF-MEMS and make sure that the MEMS exposure to the radiation environment is kept to an acceptable level. Preferably, the RF-MEMS should be fully protected behind e.g. the ground plane of the antenna.
Furthermore, the usually high number of controls in a reconfigurable array or reflect-array antenna may lead to a rather complex design with too high mass and too much power consumption. Therefore, it is highly recommended to investigate in this activity the possibility of reducing the number of controls (phase shifters) without sacrificing too much the antenna performance.