Multibeam antennas for global satellite coverage: theory and design

Today there is an increasing request for high-throughput communication payloads in satellite communications. Capacity in the order of 100 Gbit/s is becoming available and further significant improvement is expected in the coming years. A key element in order to guarantee this high performance is constituted by the multibeam antennas, able to generate multiple narrowly focused spot beams with frequency and polarisation reuse. Direct radiating arrays are able to generate multibeam coverage with a single aperture with the possibility of reconfiguring the coverage and the power distribution among the beams. Sparse arrays permit to reduce the number of radiators and to increase the DC to RF power efficiency by exploiting a 'space tapering' instead of an 'amplitude tapering', typically adopted in periodic arrays to control the sidelobe level. In this study, a deterministic procedure for the design of large planar sparse arrays is extended to the case, where the antenna, from a geostationary satellite, has to generate a multibeam coverage on the full Earth. The synthesis procedure is presented and validated with several numerical examples illustrating the scanning losses, array pattern deformation during the scanning and grating lobe effects.