Antenna array (electromagnetic)
An antenna array is a set of individual antennas used for transmitting and/or receiving radio waves, connected together in such a way that their individual currents are in a specified amplitude and phase relationship. The interactions of the different phases enhances the signal in one desired direction at the expense of other directions. This allows the array to act as a single antenna, generally with improved directional characteristics (thus higher antenna gain) than would be obtained from the individual elements.
The resulting array in fact is often referred to and treated as "an antenna," particularly when the elements are in rigid arrangement with respect to each other, and when the ratio of currents (and their phase relationships) are fixed. On the other hand, a steerable array may be fixed physically but has electronic control over the relationship between those currents, allowing for adjustment of the antenna's directionality without requiring physical motion.