Lunar Antenna tracking of Earth
For Moon to Earth communications it should not be necessary to track the motion of the Earth in the Lunar sky with an antenna. Since the earth travels about within an 8 degree region of the lunar sky, once an antenna has been pointed at this region it does not need to be moved again. The half power beamwidth for even very high gain antennas is larger than 8 degrees. For example, 35 to 40 element yagi antennas for 70 cm, with a gain of 20 to 21 dBi, have beamwidths of about 18 degrees. Only for a combination of frequencies higher than about 10 GHz and parabolic dishes larger than about 4 meters (half power beam width of 10 degrees) will it be necessary to track the earth with an antenna. A Laser communication system would fall into this category of needing to track the earth
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Updated Thu, Apr 16, 1998.