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Diagram showing directivity: the highest power density of this antenna is in the direction of the red lobe. In electromagnetics, directivity is a parameter of an antenna or optical system which measures the degree to which the radiation emitted is concentrated in a single direction.
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 ...
Three-dimensional antenna radiation patterns. The radial distance from the origin in any direction represents the strength of radiation emitted in that direction. The top shows the directive pattern of a horn antenna, the bottom shows the omnidirectional pattern of a simple vertical dipole antenna.
Patch antenna gain pattern. A directional antenna or beam antenna is an antenna which radiates or receives greater radio wave power in specific directions. Directional antennas can radiate radio waves in beams, when greater concentration of radiation in a certain direction is desired, or in receiving antennas receive radio waves from one specific direction only.
English: Diagram explaining how the directivity (directive gain) of an antenna is defined. R (grey) is the radiation pattern of a typical directive antenna. It radiates most of its power in a narrow lobe oriented along the z axis.
Antenna gain (G) is defined as antenna efficiency (e) multiplied by antenna directivity (D) which is expressed mathematically as: =. A useful relationship between omnidirectional radiation pattern directivity (D) in decibels and half-power beamwidth (HPBW) based on the assumption of a sin ( b θ ) / b θ {\displaystyle \sin(b\theta )/{b ...
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Since the directive antenna radiates the same total power within a small angle along the z axis, it can have a higher signal strength in that direction than the isotropic antenna, and so a gain greater than one. In electromagnetics, an antenna's gain is a key performance parameter which combines the antenna's directivity and radiation efficiency.