TABLE OF CONTENTS Communication satellites provide a unique perspective with which to view the earth s surface. At the geostationary altitude of 22,240 miles above the equator, they appear motionless in the sky. Serving as giant relay towers, they interconnect users in vast areas of the world who are within their continental field of view.
Due to interference considerations, communication satellites must maintain a certain separation. Therefore, only a limited number of satellites can be placed in geostationary orbit to provide communications for a region such as the United States. In addition, only certain radio frequency bands, assigned by international agreement, are available for commercial communication satellite use. The extraordinary success of satellite communication in the late 70s and early 80s threatened to exhaust both the available frequencies and the geostationary satellite positions for many regions in the world. New technology was needed to provide for this projected increase in demand. In addition to finding ways to use the existing frequency bands more efficiently, operations in the next higher frequency band (the Ka-band) were deemed necessary.
NASA s ACTS program provided new technology for increased efficiency using all radio frequencies including Ka-band. Increasing the spectrum efficiency was achieved by developing high-gain, multiple spot beam antennas and onboard switching and processing that allowed for a great increase in the number of times the same frequency could be reused by a single satellite [24]. In addition, the high-gain spot beams provided the very desirable benefit of allowing for smaller aperture user terminals at higher data...
