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Reproduction of figures extracted from the 1990 Edition of CCIR Volumes (XVIIth Plenary Assembly, Dusseldorf, 1990), the € Handbook on Satellite Communications (ITU Geneva, 1988) and the ITU-R Recommendations is made with the authorisation of the International Telecommunication Union (ITU) as copyright holder. The choice of the excerpts reproduced remains the sole responsibility of the authors and does not involve in any way the ITU.  This chapter describes the characteristics of satellite communication systems.
It aims to satisfy the curiosity of an impatient reader and facilitate a deeper understanding by directing him or her to appropriate chapters without imposing the need to read the whole work from beginning to end.  Satellite communications are the outcome of research in the area of communications and space technologies whose objective is to achieve ever increasing ranges and capacities with the lowest possible costs. The Second World War stimulated the expansion of two very distinct technologies—missiles and microwaves

The expertise eventually gained in the combined use of these two techniques opened up the era of satellite communications. The service provided in this way usefully complements that previously provided exclusively by terrestrial networks using radio and cables. The space era started in 1957 with the launching of the first artificial satellite (Sputnik). Subsequent years have been marked by various experiments including the following: Christmas greetings from President Eisenhower broadcast by SCORE (1958), the reflecting satellite ECHO (1960), store-and-forward transmission by the COURIER satellite (1960).
Powered relay satellites (TELSTAR and RELAY in 1962) and the first geostationary satellite SYNCOM (1963). In 1965, the first commercial geostationary satellite INTELSAT I (or Early Bird) inaugurated the long series of INTELSATs; in the same year, the first Soviet communications satellite of the MOLNYA series was launched. The first satellites provided a low capacity at a relatively high cost; for example, INTELSAT I weighed 68 kg at launch for a capacity of 480 telephone channels and an annual cost of $32 500 per channel at the time. This cost resulted from a combination of the cost of the launcher, that of the satellite, the short lifetime of the satellite (1.5 years) and itslow capacity.

The reduction in cost is the result of much effort which has led to the production of reliable launchers which can put heavier and heavier satellites into orbit (typically 5900 kg at launch in 1975, reaching 10 500 kg by Ariane 5 ECA and 13 000 kg by Delta IV in 2008). In addition, increasing expertise in microwave techniques has enabled realisation of contoured multibeam antennas whose beams adapt to the shape of continents, frequency re-use from one beam to the other and incorporation of higher power transmission amplifiers. Increased satellite capacity has led to a reduced cost per telephone channel. In addition to the reduction in the cost of communication, the most outstanding feature is the variety of services offered by satellite communications systems.
Originally these were designed to carry communications from one point to another, as with cables, and the extended coverage of the satellite was used to set up long distance links; hence Early Bird enabled stations on opposite sides of the Atlantic Ocean to be connected. However, as a consequence of the limited performance of the satellite, it was necessary to use earth stations equipped with large antennas and therefore of high cost (around $10 million for a station equipped with a 30m diameter antenna). The increasing size and power of satellites has permitted a consequent reduction in the size of earth stations