Multifunction Radar

Early radar systems used antenna arrays formed by the combination of individual radiators. Such antennas date back to the turn of the twentieth century.1 ^,2 ^,3 Antenna characteristics are determined by the geometric position of the radiators and the amplitude and phase of their excitation. As radars progressed to shorter wavelengths, arrays were displaced by simpler antennas such as parabolic reflectors. For modern radar applications the advent of electronically controlled phase shifters and switches has once more directed attention to array antennas. The aperture excitation may now be modulated by controlling the phase of the individual elements to give beams that are scanned electronically. This chapter will be devoted to arrays of this type.

The capability of rapidly and accurately switching beams permits multiple radar functions to be performed, interlaced in time or even simultaneously. An electronically steered array radar may track a great multiplicity of targets, illuminate a number of targets with RF energy and guide missiles toward them, perform complete hemispherical search with automatic target selection, and hand over to tracking. It may even act as a communication system, directing high-gain beams toward distant receivers and transmitters. Complete flexibility is possible; search and track rates may be adjusted to best meet particular situations, all within the limitations set by the total use of time. The antenna beamwidth may be changed to search some areas more rapidly with less...