For most terrestrial communications, rather, there is an advantage in reducing radiation toward the sky or ground in favor of horizontal direction(s).ДЄ dipole antenna oriented horizontally sends no energy in the direction of the conductor вЂ“ this is called the antenna null вЂ“ but is usable in most other directions. A hypothetical antenna that radiates equally in all vertical as well as all horizontal angles is called an isotropic radiator however these cannot exist in practice nor would they be particularly desired. Since antennas obey reciprocity the same radiation pattern applies to transmission as well as reception of radio waves. A so-called beam antenna is unidirectional, designed for maximum response in the direction of the other station, whereas many other antennas are intended to accommodate stations in various directions but are not truly omnidirectional. A receiving antenna may include not only the passive metal receiving elements, but also an integrated preamplifier or mixer, especially at and above microwave frequencies.ДЄn automobile's whip antenna, a common example of an omnidirectional antenna.ДЄntennas can be classified as omnidirectional, radiating energy approximately equally in all horizontal directions, or directional, where radio waves are concentrated in some direction(s). ДЄntenna may refer broadly to an entire assembly including support structure, enclosure (if any), etc., in addition to the actual functional components. Because of his prominence, Marconi's use of the word antenna spread among wireless researchers and enthusiasts, and later to the general public. Until then wireless radiating transmitting and receiving elements were known simply as вЂњterminalsвЂќ. In Italian a tent pole is known as l'antenna centrale, and the pole with the wire was simply called l'antenna. In the summer of 1895, Marconi began testing his wireless system outdoors on his father's estate near Bologna and soon began to experiment with long wire 'aerials' suspended from a pole. The origin of the word antenna relative to wireless apparatus is attributed to Italian radio pioneer Guglielmo Marconi. Occasionally the equivalent term вЂњaerialвЂќ is used to specifically mean an elevated horizontal wire antenna. The words antenna and aerial are used interchangeably. 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 вЂњbeamвЂќ antennas). ДЄn 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 or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver.

In this animation the action is shown slowed down enormously. Loops of electric field leave the antenna and travel away at the speed of light these are the radio waves. The transmitter applies an alternating electric current to the rods, which charges them alternately positive (+) and negative (в€’). The antenna in the center is two vertical metal rods connected to a radio transmitter (not shown). Animation of a half-wave dipole antenna radiating radio waves, showing the electric field lines.

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