This article is from the Satellite TV FAQ, by Gary Bourgois email@example.com with numerous contributions by others.
The feedhorn acts as a microwave "funnel" if you want to think of
it that way. This device places the LNB at the focus of the dish,
and is usually just called "the feed". There are several different
types of feeds.
Single C band feed: Contains ONE C band LNB. A device called
a POLAROTOR is located inside, which allows the reception of
both vertically polarized and horizontally polarized channels.
In general practice, the EVEN channels are on ONE polarity and
the ODD channels are on the opposite polarity. The actual
polarity scheme depends on the satellite in question.
Dual C band feed: Allows the use of Two C band LNB's one for
horizontal polarization and one for vertical.
Dual Band Feed (C and KU): Has two separate LNB's, one for C
band and one for KU band.
DUAL C band and single KU band feed: (There is at least one
version of this type of feed.
The most popular Dual Band feedhorns are the Chaparral CO-ROTOR II
Gardiner and ADL, though there are others on the market. While these
are actually a compromise system, with some minor losses, in
practice they work pretty well.