L-band antenna systems design

The INMARSAT-3 satellite requires a complex set of spot beam coverage and isolations in order to provide high EIRP and L-band services to land, sea and air mobile users. The spacecraft must also provide a lower EIRP service via a global beam to maintain present services to higher gain mobile users. The solution has been to use 22 feeds on a lattice with seven fold circular symmetry. This departure from conventional square or hexagonal arrangements has been introduced to cause the beams to adopt a sevenfold circular symmetry around the Earth's rim: this pattern most closely maps to that of INMARSAT's requirements while maintaining circular symmetry-essential for a high gain global beam. A multimatrix amplifier used in conjunction with a focal plane array fed reflector allows an efficient control of multiple feeds and a high degree of feed sharing between beams.