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Since a half-wave dipole has a gain of 2.19 dBi and a radiation resistance of 73 Ohms, a quarter-wave ( 1 / 4 λ) monopole will have a gain of 2.19 + 3.0 = 5.2 dBi and a radiation resistance of about 36.5 Ohms. [13] The antenna is resonant at this length, so its input impedance is purely resistive.
Typical feeder loops are 1 / 8 to 1 / 5 the size of the antenna's main loop, which gives transform ratios of 64:1 to 25:1, respectively. Adjusting the proximity and angle of the feeder loop to the main loop, and distorting the feeder's shape, both make small-to-moderate changes to the transform ratio, and allows for fine ...
The length of a whip antenna is determined by the wavelength of the radio waves it is used with. Their length varies from compact electrically short antennas 1 / 10 wavelength long, up to 5 / 8 wavelength to improve directivity. The most common type is the quarter-wave whip, which is approximately 1 / 4 wavelength long.
A 1 / 4 λ monopole antenna and its ground image together form a 1 / 2 λ dipole that radiates only in the upper half of space. The vertical, Marconi, or monopole antenna is a single-element antenna usually fed at the bottom (with the shield side of its unbalanced transmission line connected to ground). It behaves essentially ...
Collinear dipole array on repeater for radio station JOHG-FM on Mt. Shibisan, Kagoshima, Japan. In telecommunications, a collinear antenna array (sometimes spelled colinear antenna array) is an array of dipole or quarter-wave antennas mounted in such a manner that the corresponding elements of each antenna are parallel and collinear; that is, they are located along a common axis.
The most common monopole is a vertical, 1 / 4 wave tall, which is the minimum size for it to self-resonate. [n] A one-quarter wave monopole has a gain of 5.12 dBi when mounted over a good ground plane.
Antenna directivity is the ratio of maximum radiation intensity (power per unit surface) radiated by the antenna in the maximum direction divided by the intensity radiated by a hypothetical isotropic antenna radiating the same total power as that antenna. For example, a hypothetical antenna which had a radiated pattern of a hemisphere (1/2 ...
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.