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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 Hertzian dipole or elementary doublet refers to a theoretical construction, rather than a physical antenna design: It is an idealized tiny segment of conductor carrying a RF current with constant amplitude and direction along its entire (short) length; a real antenna can be modeled as the combination of many Hertzian dipoles laid end-to-end.
Also called a multi-dipole – a common broadband and / or wideband dipole variant that superficially resembles the bow-tie antenna, but is electrically different. It is a composite of pairs of dipole arms; both arms of one of the dipoles are equal-length, but each dipole pair is a different length from every other pair.
The J-pole antenna is an end-fed omnidirectional half-wave antenna that is matched to the feedline by a shorted quarter-wave parallel transmission line stub. [5] [1] [6] For a transmitting antenna to operate efficiently, absorbing all the power provided by its feedline, the antenna must be impedance matched to the line; it must have a resistance equal to the feedline's characteristic impedance.
In general terms, at any given frequency the log-periodic design operates somewhat similar to a three-element Yagi antenna; the dipole element closest to resonant at the operating frequency acts as a driven element, with the two adjacent elements on either side as director and reflector to increase the gain, the shorter element in front acting ...
Patterned Vivaldi antenna, made from double-sided printed circuit board material. The feedline excites an open space via a microstrip line or coaxial cable, and may be terminated with either a sector-shaped area or a direct coaxial connection. From the open space, the signal traverses an exponentially tapered pattern via a symmetrical slot line.
Biconical antennas are broadband dipole antennas, typically exhibiting a bandwidth of three octaves or more. A common subtype is the bowtie antenna, essentially a flattened version of the biconical design which is often used for short-range UHF television reception. These are also sometimes referred to as butterfly antennas. [2]
Consider a Yagi–Uda consisting of a reflector, driven element, and a single director as shown here. The driven element is typically a 1 ⁄ 2 λ dipole or folded dipole and is the only member of the structure that is directly excited (electrically connected to the feedline). All the other elements are considered parasitic. That is, they ...