Phase Conjugation in Optics and Radio

Basic physics and properties of the phenomenon of phase conjugation (PhC) are clarified. A brief information is given about the first works on PhC, which appeared first in radio engineering and shortly after in optics. The main optical methods of implementing PhC and the suggested ways of using the phenomenon as applied to laser radiation. In the field of radio, estimates are given that reveal an opportunity of realizing PhC despite medium variations in time. Problems concerning the design and features of self-phased antenna arrays, the means of relizing PhC, and its practical applications are considered in the main.