Design and development of linear and circular polarized C-band offset Gregorian reflector antenna for VSAT application

Advances in communication satellite industry have made it possible to utilize smaller antennas in two-way communications networks, commonly known as VSAT (very small aperture terminal) networks. These typically range in aperture size from 60 cm to 4.5 m. It is now possible to build a system with antennas having significantly less gain than the conventional 3.8 m reflector antenna satisfying the 2/spl deg/ satellite spacing. However, the most driving criteria is to meet the FCC, ITU and similar sidelobe requirements which call for off-main beam radiation to satisfy 29-25 log /spl theta/ envelope for antennas having D//spl lambda/<50. For frequency re-use satellites radiation for cross-polarized components frequently have to be controlled to better than 30 dB cross-polarization in the 1 dB contour. A conventional solution is to use an offset reflector antenna with large focal to diameter ratio (f/d) in order of 1.1 or larger. However, the design and manufacturing of reflector support structure, shipping, and installation costs of such antennas do not allow the full realization of compactness, and possible cost reductions in the communication system. Prodelin has developed an offset Gregorian reflector antenna with main reflector diameter of 2.4 m, f/d ratio of 0.6, and RF performance which is designed to meet FCC sidelobe specifications, and ASIASAT, and Eutelsat standard-M cross-polarization requirements. This antenna is discussed.