Numerical optimization of a satellite SHF nulling multiple beam antenna

Satellite uplink antennas for SHF band communications may require high resolution adaptive nulling capability to provide sufficient pattern gain to desired users while maintaining pattern nulls on interference sources in close proximity to the users. Multiple beams antennas (MBA) consisting of an aperture illuminated by a collection of feeds located in its focal plane and a beam-forming network (BFN) for combining the outputs of the feed array are well-suited as nulling antennas for geosynchronous satellites. Demanding nulling performances in terms of interfering signals cancellation requires an accurate pattern prediction down to sidelobe level and a high cross-polar isolation of the radiated element beams. To meet these requirements, design methods and analysis tools have been employed that take into account the electromagnetic interaction among the feeders and the satellite structures. In the qualification phase of an SHF nulling MBA at AASI, the pattern measurements have shown an unpredicted cross-polar level due to the interaction of primary radiated field with the surrounding structures. This paper reports the main steps of the AASI and IDS activity in optimizing the antenna position and the shape of some antenna-farm structures in order to improve the cross-polar performance while considering mechanical constraints. The electromagnetic analyses have been carried out employing different numerical techniques to validate the results and reduce the risks of satellite structural modifications. The numerical techniques, the optimization procedure and measured results are reported and discussed.