Feature and application of parabolic antenna
Parabolic antenna is a bowl type antenna with the reflector by which shape becomes a parabola curved surface. Recently, BS and the CS antenna seen well are typical of that. It is called the dish antenna from the shape.
Feature of parabolic antenna
The feature of the parabolic antenna is that the directivity is sharp and the leakage of the electric wave the side and behind is a little. The parabolic antenna is basically wideband because it doesn't have the frequency response though influenced the gain and beamwidth by the reflector. I think that the influence of the radiation machine is large of the frequency response.
Radiation machine of parabolic antenna
The one that not is because of gains such as 1/2 wavelength dipole antennas and the horn antennas is used well for the first radiation machine put on the focus of the parabolic antenna.
This is because high interest need not be especially gained because it originally obtains profitable high interest with the reflector in the radiation machine. However, Yagi Antenna might be used for the radiation machine of the parabolic antenna. The purpose of this is to raise the gain of the antenna comparatively even a little by UHF of a low frequency. Yagi Antenna of 2-3 elements is used well.
Shape and size of reflector of parabolic antenna
Because the shape of the reflector of the parabolic antenna is paraboloid shape, neither the design nor production are easy. Therefore, there is the one that the design and production comparatively used the reflector on an easy sphere, too. It is used from no so much change of the performance even if the shape is not severe well for a low frequency like UHF belt especially.
There is a caliber of the reflector of a paraboloid type from the one of the size of domestic BS and CS up to the one of 100 meters or more like tens of-meter for satellite communication one and radio telescope, etc.
Transformation antenna of parabolic antenna
Parabolic antenna with sub-reflector
The reflector of a paraboloid type is made a main reflector, the sub-reflector is put on the focus instead of the first radiation machine, and there is an antenna to put the first radiation machine on the vicinity of the surface of a main reflector.
This is seen well in a large-scale parabolic antenna like the earth station of the satellite communication and a super radio telescope.
Offset parabolic antenna
The oval parabolic antenna often seen with the antenna for satellite broadcasting is called an offset parabolic antenna. This reflector is use only of a paraboloid part.
Because the first neither radiation machine nor the bolster block traffic as shown in the electric wave, the loss of the antenna is made a minimum. Moreover, there is an advantage that the snow accretion in the snowy country is suppressed because the parabola part approaches vertically when the radiation machine is arranged downward in the parabola part.
Oppositely, when the radiation machine is arranged up in the parabola part, the parabola part approaches horizontally. Then, the monopoly area of the entire antenna becomes small and it is suitable as the indoor antenna. This has been described in detail to the article on "Production of the attachment lug for BS indoor antenna" in this homepage.