History
The idea of using parabolic reflectors for radio antennas was taken from optics, where the power of a parabolic mirror to focus light into a beam has been known since classical antiquity. The designs of some specific types of parabolic antenna, such as the Cassegrain and Gregorian, come from similarly named analogous types of reflecting telescope, which were invented by astronomers during the 15th century.
German physicist Heinrich Hertz constructed the world's first parabolic reflector antenna in 1888. The antenna was a cylindrical parabolic reflector made of zinc sheet metal supported by a wooden frame, and had a spark-gap excited dipole along the focal line. Its aperture was 2 meters high by 1.2 meters wide, with a focal length of 0.12 meters, and was used at an operating frequency of about 450 MHz. With two such antennas, one used for transmitting and the other for receiving, Hertz demonstrated the existence of radio waves which had been predicted by James Clerk Maxwell some 22 years earlier. However, the early development of radio was limited to lower frequencies at which parabolic antennas were unsuitable, and they were not widely used until after World War 2, when microwave frequencies began to be exploited.
Italian radio pioneer Guglielmo Marconi used a parabolic reflector during the 1930s in investigations of UHF transmission from his boat in the Mediterranean. In 1931 a microwave relay link across the English Channel using 10 ft. (3 meter) diameter dishes was demonstrated. The first large parabolic antenna, a 9 m dish, was built in 1937 by pioneering radio astronomer Grote Reber in his backyard, and the sky survey he did with it was one of the events that founded the field of radio astronomy. The development of radar during World War II provided a great impetus to parabolic antenna research, and saw the evolution of shaped-beam antennas, in which the curve of the reflector is different in the vertical and horizontal directions, tailored to produce a beam with a particular shape. During the 1960s dish antennas became widely used in terrestrial microwave relay communication systems.
The first parabolic antenna used for satellite communications was constructed in 1962 at Goonhilly in Cornwall, England, UK to communicate with the Telstar satellite. The Cassegrain antenna was developed in Japan in 1963 by NTT, KDDI and Mitsubishi Electric. The advent in the 1970s of computer design tools such as NEC capable of calculating the radiation pattern of parabolic antennas has led to the development of sophisticated asymmetric, multireflector and multifeed designs in recent years.
Read more about this topic: Parabolic Antenna
Famous quotes containing the word history:
“The history of the genesis or the old mythology repeats itself in the experience of every child. He too is a demon or god thrown into a particular chaos, where he strives ever to lead things from disorder into order.”
—Ralph Waldo Emerson (1803–1882)
“The thing that struck me forcefully was the feeling of great age about the place. Standing on that old parade ground, which is now a cricket field, I could feel the dead generations crowding me. Here was the oldest settlement of freedmen in the Western world, no doubt. Men who had thrown off the bands of slavery by their own courage and ingenuity. The courage and daring of the Maroons strike like a purple beam across the history of Jamaica.”
—Zora Neale Hurston (1891–1960)
“Social history might be defined negatively as the history of a people with the politics left out.”
—G.M. (George Macaulay)