RADIATION PATTERN

Radiation pattern 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 directivepattern of a horn antenna, the bottom shows the omnidirectionalpattern of a dipole antenna. In the field of antennadesign the termradiation pattern(orantenna patternorfar-field pattern) refers to thedirectional(angular) dependence of the strength of the radio wavesfrom the antenna or other source. [ 1 ] [ 2 ] [ 3 ] Particularly in the fields of fiber optics, lasers, and integrated optics, the term radiation pattern may also be used as a synonym for the near-fieldpatternorFresnel pattern. [ 4 ]This refers to thepositionaldependence of the electromagnetic fieldin the 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. [ 1 ] [ 4 ] The far-field pattern of an antenna may be determined experimentally at an antenna range, or alternatively, the near-field pattern may be found using a near-field scanner, and the radiation pattern deduced from it by computation. [ 1 ]The far-field radiation pattern can also be calculated from the antenna shape by computer programs such as NEC. Other software, like HFSScan 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, including; the field strengthat a constant (large) radius (anamplitude patternorfield pattern), the power per unit solid angle (power pattern) and the directive gain. Very often, only the relative amplitude is plotted, normalized either to the amplitude on the antenna boresight, or to the total radiated power. The plotted quantity may be shown on a linear scale, or in dB. The plot is typically represented as a three-dimensional graph (as at right), or as separate graphs in the vertical planeand horizontal plane. This is often known as apolar diagram.