Description
This work extends a previous activity under ESA/ESTEC Contract No. 19075/05/NL/NH that derived the RF performance achievable if the four-reflector single-feed-per-beam multibeam antenna system often used on Ka-band high-throughput satellites is replaced by one oversized shaped reflector antenna. The previous activity demonstrated the feasibility of the oversized reflector, but also identified limitations due to degradations of scanned beams caused by the offset-reflector astigmatism. Similar but smaller scan degradations occur in the four-reflector system. Multiple-feed-per-beam reflector systems provide some scan-degradation compensation but many feeds are required in severe cases. This activity aims at overcoming the scan limitations of the oversized shaped reflector by modifying each single-feed-per-beam feed horn depending on scan angle and scan direction. We use an array to represent each single-feed-per-beam feed horn. The figure illustrates one of the three array approaches considered.
The presentation will discuss merits and demerits of various approaches and results obtained for optimised array phase excitations - assumed to vary linearly with frequency – for various amplitude distributions. One objective is to reduce the complexity by minimising the number of designs required. Another objective is to combine receive and transmit operation.
