Offset dish antenna
Encyclopedia
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 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.
Parabolic antenna
A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or parabolic dish...
. It is so called because the antenna feed
Antenna feed
In telecommunications and electronics, an antenna feed refers to the components of an antenna which feed the radio waves to the rest of the antenna structure, or in receiving antennas collect the incoming radio waves, convert them to electric currents and transmit them to the receiver...
is offset to the side of the reflector, in contrast to a typical axial-fed parabolic antenna
Parabolic antenna
A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or parabolic dish...
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
Paraboloid
In mathematics, a paraboloid is a quadric surface of special kind. There are two kinds of paraboloids: elliptic and hyperbolic. The elliptic paraboloid is shaped like an oval cup and can have a maximum or minimum point....
, 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 direct-broadcast satellite dishes used for satellite television
Satellite television
Satellite television is television programming delivered by the means of communications satellite and received by an outdoor antenna, usually a parabolic mirror generally referred to as a satellite dish, and as far as household usage is concerned, a satellite receiver either in the form of an...
, where the feed structure is large enough in relation to the dish to block a significant proportion of the signal.
External links
- Offset-fed Parabolic Dish Antennas by Paul Wade