Offset dish antenna

Main types of parabolic antennas

An offset dish antenna is a type of parabolic antenna. It is so called because the antenna feed is offset to the side of the reflector, in contrast to a typical axial-fed parabolic antenna where the feed is in front of the dish, on its axis. As in an axial-fed parabolic dish, the feed is located at the focal point of the reflector, but the reflector is an asymmetric segment of a paraboloid, so the focus is located to the side.

The purpose of this design is to avoid the feed blocking the beam. In an ordinary axial-fed dish antenna, the feed structure and its supports are located in the path of the beam of radio waves, partially obstructing them. In the offset design, the feed is positioned outside the area of the beam. It is used for small parabolic antennas or "mini-dishes", such as the K_u band direct-broadcast satellite dishes used for satellite television, where the feed structure is large enough in relation to the dish to block a significant proportion of the signal.

See also

• axi-symmetric

External links

• Offset-fed Parabolic Dish Antennas by Paul Wade