SATELLITE COMMUNICATIONS SYSTEM

The proposed satellite communications system comprises ground stations, one of which acts as the communications centre, and a repeater serving an artificial earth satellite. Each ground station contains a data input/output unit (1) which connects the subscriber unit and is connected in the appropriate way to a shaper (19) which shapes the request frame for establishing communications, a frequency synthesiser (2), a unit (11) for switching the ground station from one operating mode to another when service signals and subscriber data are received and transmitted and based on a processor, and controlling the frequency synthesiser (2) and shaper (19) of the request frame for the establishment of communications. Once processed in the receiving circuit, the communication establishment request interrogation signals and the characteristics of the body of data to be transmitted enter the unit (11) from the communications centre. From the shaper (19) the signal, after being processed in the receiving circuit, is transmitted via the antenna (7) to the repeater. The repeater is divided into N circuits and is provided with N multiple beam antennas (12) which produce fixed two-way beams. After undergoing filtering in the filters (14.1.1...14.1.N) and level adjustment in the attenuators (15.1.1...15.1.N), the signals combine at N summators. The group signal after conversion is emitted by the appropriate antenna (12.1...12.N) in the direction of one of the areas of coverage; the value of N depends on the ratio of the angular dimensions of the common area of coverage to the beam width of each antenna of the repeater circuit. This design of a satellite communications system maximises the penetrating power while reducing power consumption and reducing bandwidth through regulation of communications. L'invention a pour objet un système de télécommunication par satellite comprenant des stations au sol, chacune d'elle agissant comme centre de télécommunication, et un répéteur monté sur un satellite artificiel de la Terre. Chaque station au sol comporte une unité d'entrée/sortie de données (1) reliant le poste de l'abonné et reliée de façon appropriée à un circuit de mise en forme (19) qui met en forme la trame de demande d'établissement de communications. Chaque station comporte en outre un synthétiseur de fréquences (2), une unité (11) conçue pour commuter la station au sol d'un mode de fonctionnement à l'autre, lorsque des signaux de service et des données de l'abonné sont reç