An isotropic radiator is a hypothetical source radiating power equally in all directions. For a given element spacing, the phase shift between any two element currents can be chosen to give perfect cancellation in any desired direction. This is called "null placement ". The bore sight direction is at zero azimuth and elevation angles and is the direction of strongest radiation in the polar pattern. Boresight: direction(s) of maximum gain, or directivity, or radiated field strength The main beam consists of the radiation between boresight direction and the first null. The azimuth angle is measured between the boresight direction and the radiation direction in the horizontal plane. The elevation angle is measured between the boresight direction and the radiation direction in the vertical plane. The side lobes consist of continuous regions of radiation between nulls, discounting the main beam. Nulls are directions in which there is no radiation. Vertical polarization occurs when the electric field vector has components in the vertical direction An isotropic source radiates equally in all directions in both azimuth and elevation angles while an omnidirectional antenna radiates uniformly in all azimuth directions, but has a deep null in the orthogonal elevation direction.
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