Discussion
Why does pointing a dish antenna closer to the horizon raise its noise temperature?
Answer: C
At low elevation the main beam looks through much more atmosphere, which is warm and lossy, and the side lobes increasingly see ground at about 290 kelvin instead of cold sky. Both raise the noise temperature and reduce the ratio of gain to system temperature. Gain itself does not change with pointing, polarisation rotation is a separate ionospheric effect, and the physical temperature of the feed is unchanged. This is why satellite earth stations specify a minimum elevation angle.
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