phased array

This article is about general theory and electromagnetic phased array. For the ultrasonic and medical imaging application, see phased array ultrasonics.In wave theory, a phased array is a group of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions. This technology was originally developed by future Nobel Laureate Luis Alvarez during World War II as a rapidly-steerable radar system for "ground-controlled approach", a system to aid in the landing of airplanes in England. (GEMA in Germany built at the same time the PESA Mamut1. ) It was later adapted for radio astronomy, leading to Physics Nobel Prizes for Antony Hewish and Martin Ryle after several large phased arrays were developed at Cambridge University. The design is also used in radar, and is generalized in interferometric radio antennas.
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A group of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions. (188 ) Note 1: The relative amplitudes of--and constructive and destructive interference effects among--the signals radiated by the individual antennas determine the effective radiation pattern of the array. Note 2: A phased array may be used to point a fixed radiation pattern, or to scan rapidly in azimuth or elevation.