Electronically scanned antenna systems

Electronic scanning allows the direction, shape, or rate of change of direction of an antenna beam to be varied faster than is possible by mechanical movement of the aperture. The principal application is in advanced radar systems. Scanning may be in one or two dimensions, using linear, planar, circular or orthogonal apertures. Control may be by mechanical, ferrite, diode or circuit-type phase shifters, or by frequency variation. This control may be applied directly to the aperture, or indirectly by means of some collimation system. The most cost-effective solution to any given scanning problem is usually the configuration that provides no more facilities than the application is able to exploit. During the last two decades, antenna-scanning capabilities have exceeded requirements and few advanced systems have gone into production. However, appropriate applications are now emerging, and a steady but unspectacular growth in electronic scanning may be expected.