Twenty years of international satellite communication

This paper reviews the development of international satellite communications over the past two decades. To date over 100 satellites have been launched to provide both domestic and overseas commercial (i e., non-military) communications services and this paper largely confines itself to describing the technical developments involved in creating the INTELSAT system which are representative of the field as a whole INTELSAT, is an international organization established in 1964 to provide overseas communications It has developed a global system designed to provide (1) a high degree of connectivity and (2) a large communications capacity. Connectivity has been achieved using relatively broad (albeit “shaped”) satellite antenna patterns permitting earth stations in many countries that are illuminated by the same beam to be interconnected. This desirable attribute has, however, required the use of large earth stations and one future technical direction is likely to entail using satellites that generate narrow pencil beams permitting the use of smaller earth stations; on-board switching will then be required to restore connectivity between beams. A large capacity has been achieved through the use of “frequency reuse,” i e., techniques to utilize the C-band frequencies assigned for satellite communications several-fold This has been accomplished through satellite designs that employ isolated antenna beams to illuminate different parts of the earth and/or beams that view overlapping parts but employ opposite senses of (circular) polarization. Associated with this approach have been efforts to use the assigned bands as efficiently as possible through “channelization,” i.e., subdividing them into frequency intervals, each of which is served by a transponder amplifier designed to yield minimum interference with its neighbors. The paper concludes with a brief discussion of the likely trends in the design of satellite systems as these evolve in competition with fiber-optic cables.