Patent ID: 6014372
Filing Date: 2000-01-11
Classification: H04B

Abstract:
A spacecraft cellular communication system, comprising:a spacecraft including a body;a receiving and frequency conversion arrangement mounted on said body, for receiving signals from terrestrial stations, and for converting signals received from terrestrial stations at specific frequencies within a first frequency band to other frequencies in a second frequency band, which second frequency band does not include said first frequency band;at least one antenna supported by said body, said antenna including an array of radiating elements and a first plurality of signal input ports coupled to said radiating elements of said array of radiating elements;a beamforming network mounted on said body, said beamforming network including plural input ports coupled to said receiving and frequency conversion arrangement, and a plurality of output ports coupled to said signal input ports of said antenna array, for receiving signals at said other frequencies within said second frequency band at said plural input ports, and for combining said signals at said other frequencies in a manner which, in combination with said antenna, generates a plurality of spot radiation beams directed toward the Earth's surface, said spot radiation beams defining overlapping footprints, for transmitting signals at said other frequencies from said spacecraft to terrestrial user terminals located within said footprints;a fixed terrestrial terminal lying within the overlap region between at least first and second specific ones of said spot beams, for transmitting signals to said spacecraft at some of said specific frequencies within a first frequency range, for transmission of information signals to at least some of said terrestrial user terminals, whereby antenna positional errors may cause said spot beams to be misdirected; andan antenna positioning arrangement, said antenna positioning arrangement comprising:(a) beacon signal transmitting means located at said fixed terrestrial terminal, for transmitting beacon signals to said receiving and frequency conversion arrangement at a beacon frequency lying within said first frequency band, whereby said receiving and frequency conversion means converts said beacon signals lying within said first frequency band to beacon signals lying within said second frequency band;(b) coupling means coupled to said receiving and frequency conversion means and to at least one of said input ports of said beamforming network, for coupling said beacon signals to said beamforming network in a manner which generates said first and second specific ones of said spot beams in a temporal sequence;(c) beacon signal receiving means located at said fixed terrestrial terminal, for receiving said beacon signals at said second frequency band in said temporal sequence;(d) error determining means coupled to said beacon signal receiving means, for comparing characteristics of said beacon signals in said temporal sequence, to determine pointing error of said antenna; and(e) control means coupled to said error determining means, for generating control signals for tending to move said spot beams to a condition in which said beacon signals in said temporal sequence have a common value of at least one of said characteristics.