ABSTRACT

All early radars utilized single large antennas such as parabolic reflectors. Such radars operate by transmitting a focused beam in the direction of interest. Generally such antennasmechanically rotate in azimuth and also often in elevation in order to provide full beam coverage.Many of the older radars were relatively low in frequency and required a large antenna. As radars progressed, particularly to higher frequencies, it became viable and advantageous to consider antennas that do not rotate but are electronically steered. In electronically steered systems, the antenna can be steered slowly along the same direction or could have arbitrary search patterns allowing high priority targets to be revisited at different rates. The time on target can be increased relatively easily, and multiple simultaneous functions (such as surveillance, multiple-target tracking, illuminating targets, electronic countercountermeasures, communication, etc.) are possible. In more advanced systems today, there can be simultaneous transmission as well as reception of multiple beams.