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Radiation pattern
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{{Short description|Directional variation in strength of radio waves}} [[Image:Radiation-patterns-v.png|thumb|right|upright=1.4|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 [[Directional antenna|directive]] pattern of a [[horn antenna]], the bottom shows the [[omnidirectional antenna|omnidirectional]] pattern of a simple vertical [[dipole antenna]].]] In the field of [[Antenna (radio)|antenna]] design the term '''radiation pattern''' (or '''antenna pattern''' or '''far-field pattern''') refers to the ''directional'' (angular) dependence of the strength of the [[radio waves]] from the antenna or other source.<ref name="Balanis">Constantine A. Balanis: "Antenna Theory, Analysis and Design", John Wiley & Sons, Inc., 2nd ed. 1982 {{ISBN|0-471-59268-4}}</ref><ref name="Cheng">David K Cheng: "Field and Wave Electromagnetics", Addison-Wesley Publishing Company Inc., Edition 2, 1998. {{ISBN|0-201-52820-7}}</ref><ref name="JordanBalmain1968">Edward C. Jordan & Keith G. Balmain; "Electromagnetic Waves and Radiating Systems" (2nd ed. 1968) Prentice-Hall. {{ISBN|81-203-0054-8}}</ref> Particularly in the fields of [[fiber optics]], [[laser]]s, and [[integrated optics]], the term radiation pattern may also be used as a synonym for the '''[[Near and far field|near-field]] pattern''' or '''Fresnel pattern'''.<ref name="IEEEdict1997">Institute of Electrical and Electronics Engineers, "The IEEE standard dictionary of electrical and electronics terms"; 6th ed. New York, N.Y., Institute of Electrical and Electronics Engineers, c1997. IEEE Std 100-1996. {{ISBN|1-55937-833-6}} [ed. Standards Coordinating Committee 10, Terms and Definitions; Jane Radatz, (chair)]</ref> This refers to the ''positional'' dependence of the [[electromagnetic field]] in the [[Near and far field|near field]], or Fresnel region of the source. The near-field pattern is most commonly defined over a plane placed in front of the source, or over a cylindrical or spherical surface enclosing it.<ref name="Balanis"/><ref name="IEEEdict1997"/> The far-field pattern of an antenna may be determined experimentally at an [[antenna measurement|antenna range]], or alternatively, the near-field pattern may be found using a '''[[Electromagnetic near-field scanner|near-field scanner]]''', and the radiation pattern deduced from it by computation.<ref name="Balanis"/> The far-field radiation pattern can also be calculated from the antenna shape by computer programs such as [[Numerical Electromagnetics Code|NEC]]. Other software, like [[Ansys HFSS|HFSS]] can also compute the near field. The far field radiation pattern may be represented graphically as a plot of one of a number of related variables, like the [[field strength]] at a constant (large) radius (an '''amplitude pattern''' or '''field pattern'''), the power per unit solid angle ('''power pattern''') and the [[Antenna gain|directive gain]]. Very often, only the relative amplitude is plotted, normalized either to the amplitude on the antenna [[Antenna boresight|boresight]], or to the total radiated power. The plotted quantity may be shown on a linear scale, or in [[Decibel|dB]]. The plot is typically represented as a three-dimensional graph (as at right), or as separate graphs in the [[Vertical and horizontal|vertical plane]] and [[Vertical and horizontal|horizontal plane]]. This is often known as a '''polar diagram'''.
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