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| Antennas |
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Radiation sources / regions |
In aradio antenna, themain lobe ormain beam is the region of theradiation pattern containing the highestpower or exhibiting the greatestfield strength.
The radiation pattern of most antennas shows a pattern of "lobes" at various directions, where the radiated signal strength reaches a local maximum, separated by "nulls", at which the radiation falls to zero. In adirectional antenna in which the objective is to emit the radio waves in one direction, the lobe in that direction is designed to have higher field strength than the others, so on a graph of the radiation pattern it appears biggest; this is the main lobe. The other lobes are called "sidelobes", and usually represent unwanted radiation in undesired directions. The sidelobe in the opposite direction from the main lobe is called the "backlobe".
The radiation pattern referred to above is usually the horizontal radiation pattern, which is plotted as a function ofazimuth about the antenna, although the vertical radiation pattern may also have a main lobe. Thebeamwidth of the antenna is the width of the main lobe, usually specified by thehalf power beam width (HPBW), the angle encompassed between the points on the side of the lobe where the power has fallen to half (-3dB) of its maximum value.
The concepts of main lobe and sidelobes also apply toacoustics andoptics, and are used to describe the radiation pattern of optical systems liketelescopes, and acoustic transducers likemicrophones andloudspeakers.
This article incorporatespublic domain material fromFederal Standard 1037C.General Services Administration. Archived fromthe original on 2022-01-22. (in support ofMIL-STD-188).
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