COMSTAR Experiment: An Overview of the Bell Laboratories 19- And 28-GHz COMSTAR Beacon Propagation Experiments

Propagation experiments using the 19- and 28-GHz beacons on satellites represent a significant milestone in the quest for design information for future satellite communication systems. The experimental results also contribute to knowledge of meteorological processes. Earth-space propagation information above 10 GHz is a key component in the exploration of concepts for high-capacity domestic satellite communication systems.1-2 COMSTAR 1231 Future high-capacity satellite communication systems will probably use frequencies above 10 GHz because of the large segment of unused frequency spectrum available and because of spectrum crowding at the lower frequencies. In particular, frequency bands over 2000 MHz wide are allocated at 19 and 28 GHz, and 500 MHz bands are available at 12 and 14 GHz for common-carrier satellite communication systems; at 4 and 6 GHz the allocated frequency bands are only 500 MHz wide. Even now satellite systems at 4 and 6 GHz are severely constrained by requirements for avoiding interference with the extensive terrestrial radio networks that share these same frequency bands. New systems will probably reuse frequencies on two orthogonal polarizations to double the usable bandwidth and may reuse frequencies among spot antenna beams covering small areas of high traffic concentration. Thus, knowledge of the decrease in cross-polarization isolation produced by rain and ice is needed and satellite antenna sidelobe control will be important. Sidelobe levels of earth station antennas and the scattering of energy from one antenna beam to another by rain will limit how close communication satellites can be spaced in the geosynchronous orbit.