Page 68 - Communications Satellites Global Change Agents

44 IPPOLITO AND PELTON

A mini space race to build satellite earth stations was thus created in 1965. As
noted earlier, the most exotic of these early designs was an earth station built by
AT&T in Andover, Maine, in the shape of a huge horn antenna. It was more strik-
ing in its design that in its performance, however, and the United States and over-
seas satellite antennas that followed assumed the more traditional parabolic dish
shape that (in a variety of sizes from huge to small) has become commonplace to-
day.
The world's first operational communications satellite was what is today
called power limited. That is, its power was less that that used by a small TV or
even a good-sized light bulb. The received signal strength from "Early Bird" sat-
ellite was equivalent to a few millionths of a watt when it reached the earth's sur-
face. Therefore, to operate successfully, the first earth stations had to be ex-
tremely sensitive and possess what is called very high gain. Also the satellite
signals had to be separated from other radio transmissions sent on adjacent fre-
quencies. It is for this reason that the locations of these first earth stations were
built well away from cities or other population centers. The early locations such
as Andover, Maine, and Goonhilly Downs, United Kingdom, were about as iso-
lated (and as electronically silent) as one could find in the respective countries.
This may seem strange in today's world of powerful communications satel-
lites, which can operate with small dishes or VSATs positioned on the top of
buildings or mounted on houses (and these dishes are often less than a meter in
size). Even more remarkably, there are now hand-held user terminals for mobile
satellite communications. This is possible because in nearly 40 years satellites
have increased their net transmit power in the range of 10,000 to 100,000 times.
Instead of satellites being able to generate something like 100 watts of power,
there are now spacecraft in orbit with solar arrays that can generate many kilo-
watts.
Yet increased power is only part of the story. Even more important, today's
satellites also have extremely large, high gain antennas operating out in space that
allow radio frequency (rf) power to be focused into powerful beams. The net re-
sult is that they can generate rf signals that are, in net effect, a million times more
powerful than the Syncom or Early Bird satellites, at least when measured in
terms of the signal's flux density when the satellite signal reaches a user terminal
on the earth's surface.

SATELLITE TECHNOLOGY TRENDS

The development of satellite technology is fascinating to telecommunications en-
gineers, but not always to the general public. However, the changes that have
taken place in technology for both satellites and user terminals are important to
understanding how new networks are able to be deployed across the world and
new broadband services to expand while the cost of providing these services
plummets.