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Diagram illustrating how directivity is defined. It shows the radiation pattern of a directional antenna (R, grey) that radiates maximum power along the z-axis, and the pattern of an isotropic antenna (R iso, green) with the same total radiated power.
It is a fundamental property of antennas that the receiving pattern (sensitivity as a function of direction) of an antenna when used for receiving is identical to the far-field radiation pattern of the antenna when used for transmitting. This is a consequence of the reciprocity theorem of electromagnetics and is proved below. Therefore, in ...
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 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 ...
For most antennas the boresight is the axis of symmetry of the antenna. For example, for axial-fed dish antennas, the antenna boresight is the axis of symmetry of the parabolic dish, and the antenna radiation pattern (the main lobe) is symmetrical about the boresight axis. Most antennas boresight axis is fixed by their shape and cannot be changed.
Diagram of the electric fields (blue) and magnetic fields (red) radiated by a dipole antenna (black rods) during transmission. More complex antennas increase the directivity of the antenna. Additional elements in the antenna structure, which need not be directly connected to the receiver or transmitter, increase its directionality.
Antenna gain , which is equal to the antenna's directivity multiplied by the antenna efficiency, is defined as the ratio of the intensity (power per unit area) of the radio power received at a given distance from the antenna (in the direction of maximum radiation) to the intensity received from a perfect lossless isotropic antenna at the same ...