TABLE OF CONTENTS The three basic techniques for electronic beam steering are (1) frequency scanning, (2) beam switching, and (3) phase scanning with phase shifters. Of the three techniques, the use of phase shifters is the most popular, and considerable effort has gone into the development of a variety of phase shifters. Phase shifters can be separated into two categories: reciprocal and nonreciprocal. The reciprocal phase shifter is not directionally sensitive. That is, the phase shift in one direction (e.g., transmit) is the same as the phase shift in the opposite direction (e.g., receive). Therefore, if reciprocal phasers are used, it is not necessary to switch phase states between transmit and receive. With a nonreciprocal phaser it is necessary to switch the phaser (i.e., change phase state) between transmit and receive. Typically it takes a few microseconds to switch nonreciprocal ferrite phasers. During this time the radar is unable to detect targets. For low-pulse-repetition-frequency (PRF) radars [e.g., 200 to 500 pulses per second (pps)] this may not cause a problem. For example, if the PRF is 200 pps (or Hz), the time between pulses is 500 ?s. If the switching time for the phaser is 10 ?s, only 2 percent of the time is wasted and less than 1.0 nmi of minimum range is lost. On the other hand, if the PRF = 50 kHz, the time between pulses is 20 ?s, and it would not be possible to tolerate 10 ?s of dead time for...
