offset antenna
Offset antennas are parabolic antennas whose reflector dish has the shape of a paraboloid. The reflector surface of offset antennas is elliptical and symmetrical. The name offset comes from the fact that the focal point of the antenna mirror is not centered, but has a downward offset.
The feed horn with the LNB converter is located below the center of the dish, in contrast to the feed horn of a prime focus antenna( PFA). This means that the radiation characteristics are not affected by the radiator or the feedhorn and, in addition, the offset antenna can be aligned almost vertically. This in turn has the advantage that no snow can accumulate in the reflector dish in winter, which would lead to a change in the reflection characteristics and a reduction in the antenna gain.
The radio beams hit the reflector dish at an oblique angle and are reflected from there to the LNB converter. The offset angle is normally 21°.