Aperture size reduction using sub-beam design concepts for multiple spot beam satellites

This paper describes a method to generate a large number of spot beams for multiple-beam satellite systems using smaller apertures. This is achieved by dividing the basic spot beam which has an edge gain relative to the beam peak of 3 to -4 dB, into a number of smaller sub-beams that have lower peak gain but same edge gain as the basic spot beam. This has the effect of reducing the required peak gain for the antenna, and reducing its size. The frequency band allocated to each basic beam is divided among its constituent sub-beams. Therefore, the frequency re-use among the basic beams can be maintained. The increased number of beams in the coverage introduces some complexity in the frequency allocations, which have to be coordinated among all beams. This concept is especially applicable to phased arrays using digital beam formers (DBF). The DBF complexity is a function of the number of array elements, and is less dependent on the number of beams. Reducing the array size, and consequently reducing the number of elements helps to reduce the complexity, power and mass of the DBF.