Feedhorn

In parabolic antennas such as satellite dishes, a feed horn (or feedhorn) is a small horn antenna used to convey radio waves between the transmitter and/or receiver and the parabolic reflector. In transmitting antennas, it is connected to the transmitter and converts the radio frequency alternating current from the transmitter to radio waves and feeds them to the rest of the antenna, which focuses them into a beam. In receiving antennas, incoming radio waves are gathered and focused by the antenna's reflector on the feed horn, which converts them to a tiny radio frequency voltage which is amplified by the receiver. Feed horns are used mainly at microwave (SHF) and higher frequencies.

The feedhorn also selects the polarization of the waves to be received, which helps to attenuate unwanted signals from adjacent channels and transponders, and from other communications satellites at nearby orbital positions. This can be either horizontal or vertical if the polarization is linear, or clockwise or counterclockwise (also called left- and right-handed) if it is circular. Certain devices can also allow a feedhorn to accept both linear and circular, though these cause a slight insertion loss to all incoming signals.