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- Side_lobe abstract "In antenna engineering, side lobes or sidelobes are the lobes (local maxima) of the far field radiation pattern that are not the main lobe.The radiation pattern of most antennas shows a pattern of "lobes" at various angles, directions where the radiated signal strength reaches a maximum, separated by "nulls", angles at which the radiated signal strength falls to zero. In a directional antenna in which the objective is to emit the radio waves in one direction, the lobe in that direction has a larger field strength than the others; this is the "main lobe". The other lobes are called "side lobes", and usually represent unwanted radiation in undesired directions. The side lobe in the opposite direction (180°) from the main lobe is called the "back lobe". In transmitting antennas, excessive side lobe radiation wastes energy and may cause interference to other equipment. Classified information may be picked up by unintended receivers. In receiving antennas, side lobes may pick up interfering signals, and increase the noise level in the receiver.The power density in the side lobes is generally much less than that in the main beam. It is generally desirable to minimize the sidelobe level (SLL), which is measured in decibels relative to the peak of the main beam. The main lobe and side lobes occur for both conditions of transmit, and for receive. The concepts of main and side lobes, radiation pattern, aperture shapes, and aperture weighting, apply to optics (another branch of electromagnetics) and in acoustics fields such as loudspeaker and sonar design, as well as antenna design.For a rectangular aperture antenna having a uniform amplitude distribution (or uniform weighting), the first sidelobe is -13.26 dB relative to the peak of the main beam because for such antennas the radiation pattern has a canonical form ofSimple substitutions of various values of into the canonical equation yield the following results:For a circular aperture antenna, also having a uniform amplitude distribution, the first sidelobe level is -17.57 dB relative to the peak of the main beam because in this case, the radiation pattern has a canonical form ofwhere is the Bessel function of the first kind of order 1. Simple substitutions of various values of into the canonical equation yield the following results:A uniform aperture distribution, as provided in the two examples above, gives the maximum possible directivity for a given aperture size, but it also produces the maximum side lobe level. Side lobe levels can be reduced by tapering the edges of the aperture distribution (changing from uniformity) at the expense of reduced directivity.The nulls between sidelobes occur when the radiation patterns passes through the origin in the complex plane. Hence, adjacent sidelobes are generally 180° out of phase to each other.Because an antenna's far field radiation pattern is a Fourier Transform of its aperture distribution, most antennas will generally have sidelobes, unless the aperture distribution is a Gaussian, or if the antenna is so small, as to have no sidelobes in the visible space. Larger antennas have narrower main beams, as well as narrower sidelobes. Hence, larger antennas have more sidelobes in the visible space (as the antenna size is increased, sidelobes move from the evanescent space to the visible space).For discrete aperture antennas (such as phased arrays) in which the element spacing is greater than a half wavelength, the spatial aliasing effect causes some sidelobes to become substantially larger in amplitude, and approaching the level of the main lobe; these are called grating lobes, and they are identical, or nearly identical in the example shown, copies of the main beams. Grating lobes are a special case of a sidelobe. In such a case, the sidelobes should be considered all the lobes lying between the main lobe and the first grating lobe, or between grating lobes. It is conceptually useful to distinguish between sidelobes and grating lobes because grating lobes have larger amplitudes than most, if not all, of the other side lobes. The mathematics of grating lobes is the same as of X-ray diffraction.".
- Side_lobe thumbnail Sidelobes_en.svg?width=300.
- Side_lobe wikiPageExternalLink radPatDefs.php.
- Side_lobe wikiPageID "1754982".
- Side_lobe wikiPageRevisionID "604552007".
- Side_lobe hasPhotoCollection Side_lobe.
- Side_lobe subject Category:Antennas.
- Side_lobe subject Category:Radio_frequency_propagation.
- Side_lobe type Antenna102715229.
- Side_lobe type Antennas.
- Side_lobe type Artifact100021939.
- Side_lobe type Device103183080.
- Side_lobe type ElectricalDevice103269401.
- Side_lobe type Instrumentality103575240.
- Side_lobe type Object100002684.
- Side_lobe type PhysicalEntity100001930.
- Side_lobe type Whole100003553.
- Side_lobe comment "In antenna engineering, side lobes or sidelobes are the lobes (local maxima) of the far field radiation pattern that are not the main lobe.The radiation pattern of most antennas shows a pattern of "lobes" at various angles, directions where the radiated signal strength reaches a maximum, separated by "nulls", angles at which the radiated signal strength falls to zero.".
- Side_lobe label "Lobe secondaire".
- Side_lobe label "Side lobe".
- Side_lobe label "Уровень боковых лепестков диаграммы направленности".
- Side_lobe sameAs Lobe_secondaire.
- Side_lobe sameAs m.05td2k.
- Side_lobe sameAs Q2040092.
- Side_lobe sameAs Q2040092.
- Side_lobe sameAs Side_lobe.
- Side_lobe wasDerivedFrom Side_lobe?oldid=604552007.
- Side_lobe depiction Sidelobes_en.svg.
- Side_lobe isPrimaryTopicOf Side_lobe.
