What is the Low Gain Antenna, and where is it located?
The low-gain antenna is located on the tip of the cone (the “feed”) sticking up over the High Gain Antenna. It broadcasts its signal over a wide cone (the half-angle of the cone is almost 120 degrees), which allows it to remain in communication with Earth even when it’s not pointed directly at the Earth. This is unlike the High Gain Antenna, which sends out a much more narrowly directed signal (with a half-angle of 1/6th of a degree). In both antennas, the same amount of power is being transmitted, but the low-gain spreads that power out over a much larger area of the sky than does the high gain. This is somewhat like the difference between a bare bulb and a spotlight, both operating at the same power. Since the ground antennas that are receiving Galileo’s signal need to receive a certain amount of power in order to actually “hear” that signal, the low gain can’t handle nearly as high a data rate as the High Gain Antenna – during Jupiter operations, the low gain’s top data rate was 160
