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German physicist Heinrich Hertz first demonstrated the existence of radio waves in 1887 using what we now know as a dipole antenna (with capacitative end-loading). On the other hand, Guglielmo Marconi empirically found that he could just ground the transmitter (or one side of a transmission line, if used) dispensing with one half of the antenna, thus realizing the vertical or monopole antenna.
The monopole antenna is essentially one half of the half-wave dipole, a single 1 / 4 wavelength element with the other side connected to ground or an equivalent ground plane (or counterpoise). Monopoles, which are one-half the size of a dipole, are common for long-wavelength radio signals where a dipole would be impractically large.
An antenna may have more than one driven element, although the most common multielement antenna, the Yagi, usually has only one. For example, transmitting antennas for AM radio stations often consist of several mast radiators, each of which functions as a half-wave monopole driven element, to create a particular radiation pattern.
A Yagi–Uda antenna, or simply Yagi antenna, is a directional antenna consisting of two or more parallel resonant antenna elements in an end-fire array; [1] these elements are most often metal rods (or discs) acting as half-wave dipoles. [2] Yagi–Uda antennas consist of a single driven element connected to a radio transmitter or receiver (or ...
A coaxial antenna (often known as a coaxial dipole) is a particular form of a half-wave dipole antenna, most often employed as a vertically polarized omnidirectional antenna. History [ edit ]
The distribution of current along the two arms of a halo antenna is similar to the currents along the two arms (also a quarter wavelength long) of a half-wave dipole (see the animation there), being largest at the feedpoint and dropping to zero at the ends (the gap in the case of the halo). On the other hand, a small loop has a current which is ...
Reflective array 'billboard' antenna of the SCR-270 radar, an early US Army radar system. It consists of 32 horizontal half wave dipoles mounted in front of a 17 m (55 ft) high screen reflector. With an operating frequency of 106 MHz and a wavelength of 3 m (10 ft) this large antenna was required to generate a sufficiently narrow beamwidth to ...
The LPDA normally consists of a series of half wave dipole "elements" each consisting of a pair of metal rods, positioned along a support boom lying along the antenna axis. The elements are spaced at intervals following a logarithmic function of the frequency , known as d or sigma .