Science Fair Project Encyclopedia
The feedhorn also selects the polarity 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.
When used with a parabolic reflector or lens antenna , the phase center of the horn is usually placed at the focal point of the reflector, with the 3dB points of the horn's radiation pattern set to be at the edge of the reflector. On a satellite dish, the feedhorn is what is mounted at the end of a mast from the center of the dish, or on tripod legs mounted to the edge of the dish.
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