Area coverage adaptive nulling from geosynchronous satellites: Phased arrays versus multiple-beam antennas

Antenna design trade-offs associated with providing an area coverage communication link via a geosynchronous satellite, where the geographical area to be serviced by the associated adaptive antenna system is characterized by a narrow-cone angle directed at an a priori known region on the earth´s surface, are considered. Interference sources within and just surrounding the coverage area are adaptively nulled; interference sources located far from the coverage area are minimized by designing the antenna system to have low sidelobes outside the coverage area. This minimizes the number of adaptive channels which must be processed, with subsequent decrease in satellite weight and power requirements. The antenna design trade-off is between the phased array (PA) and the multiple-beam antenna (MBA). Three specific performance factors are considered in the MBA/PA design trade-off: susceptibility to out-of-coverage-area interference sources which use up the adaptive degrees of freedom allocated to the desired coverage area; effects of reduced link margin for low-gain thinned arrays; and nulling bandwidth restrictions imposed on spread spectrum communication systems. Three classes of PA´s are considered: filled arrays, high gain thinned arrays, and low-gain thinned arrays.