Terminology Electronic symbol for an antenna The arrows of the loops get reversed each time the current changes polarity. Īntenna radiating radio waves: The transmitter applies an alternating current (red arrows) to the rods, which charges them alternately positive and negative, emitting loops of electric field. Starting in 1895, Guglielmo Marconi began development of antennas practical for long-distance, wireless telegraphy, for which he received a Nobel Prize. Hertz placed dipole antennas at the focal point of parabolic reflectors for both transmitting and receiving. The first antennas were built in 1888 by German physicist Heinrich Hertz in his pioneering experiments to prove the existence of waves predicted by the electromagnetic theory of James Clerk Maxwell. Strong directivity and good efficiency when transmitting are hard to achieve with antennas with dimensions that are much smaller than a half wavelength. An antenna may include components not connected to the transmitter, parabolic reflectors, horns, or parasitic elements, which serve to direct the radio waves into a beam or other desired radiation pattern. Antennas can be designed to transmit and receive radio waves in all horizontal directions equally ( omnidirectional antennas), or preferentially in a particular direction ( directional, or high-gain, or "beam" antennas). Īn antenna is an array of conductors ( elements), electrically connected to the receiver or transmitter. Antennas are essential components of all radio equipment. In reception, an antenna intercepts some of the power of a radio wave in order to produce an electric current at its terminals, that is applied to a receiver to be amplified.
In transmission, a radio transmitter supplies an electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). In radio engineering, an antenna ( American English) or aerial ( British English) is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver. A stack of " fishbone" and Yagi–Uda television antennas
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