>>13681697i'm talking out of my ass here, but i also do rf engineering
sat TV antennas are high-gain meaning they are sensitive only to a small range of directions. generally a technician aims the antenna at a geosynchronous orbit satellite, one who's position in the sky appears fixed. the signal is very weak, and to minimize interference from other sources, the gain of the dish is made to be as strong as possible and it's sensitivity to things not in the direction of the satellite are reduced.
also, ray optics may not be entirely appropriate here because the wavelength of light is close to the size of the geometry in question
