On the application of coherent optical processing techniques to synthetic-aperture radar

Coherent optical systems are useful for the processing of data collected by sidelooking synthetic-aperture radars. This type of radar, which is useful for generating fine-resolution terrain imagery, has the capability of providing along-track, or azimuth, resolution which is much finer than the azimuth dimension of the radiated beam itself; however, the attainment of this finer resolution requires extensive processing of the received radar signal. In this paper the form of the returning radar signals is discussed, as are the general reasons why optical processing of these signals might be attractive. The required processing can be viewed as a multichannel weighted vector summation, matched filtering operation, or cross-correlation operation; the cross-correlation viewpoint is developed, as is a corresponding optical processor implementation. The role of a conical lens in simplifying reference-function realization is discussed. Finally, a Fresnel-lens interpretation of the recorded radar signal leads to a discussion of the strong physical analogy between a coherent radar system and a coherent optical system.