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Omnidirectional radiation patterns are produced by the simplest practical antennas, monopole and dipole antennas, consisting of one or two straight rod conductors on a common axis. Antenna gain (G) is defined as antenna efficiency (e) multiplied by antenna directivity (D) which is expressed mathematically as: =.
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A competing third criterion is the number and bandwidth of the frequenc(y/ies) that a single antenna intercepts or emits. A fourth design goal is to make the antenna directional: To project or intercept radio waves from only one vertical and / or horizontal direction as exclusively as possible. Simple antennas
The latter factor is quantified by the antenna gain, which is the ratio of the signal strength radiated by an antenna in its direction of maximum radiation to that radiated by a standard antenna. For example, a 1,000 watt transmitter feeding an antenna with a gain of 4× (equiv. 6 dBi) will have the same signal strength in the direction of its ...
The top shows the directive pattern of a horn antenna, the bottom shows the omnidirectional pattern of a simple vertical dipole antenna. In the field of antenna design the term radiation pattern (or antenna pattern or far-field pattern) refers to the directional (angular) dependence of the strength of the radio waves from the antenna or other ...
John Dunlavy invented the log-periodic antenna in 1952 while working for the United States Air Force but was not credited with it due to its "Secret" classification. [13] The University of Illinois at Urbana–Champaign had patented the Isbell and Mayes–Carrel antennas and licensed the design as a package exclusively to JFD Electronics in New ...
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] Sir Arthur Lodge is the inventor of the biconical antenna. [3] [4] Omnidirectional biconical antenna
Antennas are generally sensitive to signals only when they have a length that is a significant portion of the wavelength, or larger. Most antennas are at least 1 ⁄ 4 of the wavelength, more commonly 1 ⁄ 2 – the half-wave dipole is a very common design. For longwave use, this resulted in loop antennas tens of feet on a side, often with ...