Several antennas can be arranged in space, in different geometrical configurations, to produce a highly directional pattern [1-5]. Such a configuration of multiple antenna elements is referred to as an antenna array. In an array antenna, the fields from the individual elements interfere constructively in some directions and cancel in others. Usually, arrays consist of identical elements, although it is possible to create an array of dissimilar radiating elements.
Arrays offer the unique capability of electronic scanning of the main beam (major lobe) by changing the phase of the excitation current of each array element (phased-array antennas). Also, a large variety of radiation patterns and sidelobe levels can be achieved by controlling the magnitude of the excitation current as well. Phased-array antennas have many applications, such as radar, remote sensing, and communications.
There are five main control mechanisms that affect the overall performance of an array antenna; the array geometry (linear, circular, planar, etc., arrangement of the radiating elements), the distance of separation between adjacent elements, the amplitude current excitation of each individual element, phase excitation of each individual element, and the radiation pattern of each individual element
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