Telecommunication satellites accommodate more and more Ka-band payloads for Multimedia systems, which require moderate power per feed access. In parallel, there is BSS, or reverse BSS, to respond to the HDTV systems (“Direct to Home”), which requires large frequency bands procured by the Ka-Band. The broadcast coverages are generally global (European, CONUS, Asia…) which imply a lower antenna gain for the users. Then, the EIRP has to be compensated by higher power at the antenna feed access to comply the power link budget. Therefore, the development of a “Dual polarised high power Ka-Band feed” is of great interest for these space applications.
Thanks to large platforms (> 12 kW), the satellites are able to drastically increase the number of transponders. Considering the required EIRP for Ka-Band BSS’s, some developments are ongoing in Europe. For instance a TWTA is under qualification (170W). Once the RF channels are combined in the output multiplexer (under development), it is transmitted to the feed antenna. Therefore, it is desirable to develop a feed chain capable of handling both dual-polarisation and high RF power. Assuming 36MHz channel bandwidth in contiguous configuration and 12 channels, the total power handling with two polarisations would be 4,0 kW.
The first major concern is the thermal power, close to 200 to 400 Watts, to be dissipated in this antenna feed. Moreover, this thermal power is localised in a very small volume inside the antenna feed. The main challenge is to extract this power by using a standalone radiator to maintain the feed temperature range to [-150; +150°C].
The last proposed solution with cooper electro-deposit offers several advantages with an integration of components more important than the multilayer concept. Its losses level is approximately equivalent to silver for multilayer. The electroforming is often used for ground station applications.
This study is divided in four phases:
The activity has been successfully completed. The antenna feed architecture trade-off has been performed. The Multilayer components assembly has been selected for its compactness and its number of components, which has been minimised as far as possible. In addition, its versatility w.r.t thermal coupling or discoupling with the platform appears as a main advantage. The preferred thermal concept is the V-shape radiator one in association using thermal advanced technologies. Moreover, for this concept, the RF chain is very simple and offers [S] parameters compliant with the study requirements. During the detailed design, a new optimization of the concept has been performed to improve in particular the multipactor margins and axial-ratio. The Elementary Model composed of the Horn and the RF chain has been measured. ALL the [S] parameters and the radiating patterns are compliant with the requirements. The Multipaction analysis gives enough margins w.r.t the ECSS. The test has been performed on a representative part of the feed limited to the more sensible area and one polarisation. A power level close to 6 kW in pulse mode has been applied the breadboard without any Multipaction event which corresponds to 12kW effective on the full Ka-band feed. This level corresponds to 4.7dB margin w.r.t the operational input power.