Holographic and Tomographic Imaging with Microwaves and Ultrasound

Microwave and acoustic holographic imaging experienced considerable interest during the period 1970-80 because of its diagnostic potential. The high lateral resolution of the CW/ synthetic aperture approach vis-a-vis echo timing carries the penalty of poor depth resolution so that long wavelength holography was essentially two dimensional at that time. However, it does provide a ’phase image1 which is particularly useful in reflector antenna diagnostics. The limitations of quadratic correction focusing and single view imaging (inherited from optical holography) have been removed by the adoption of inverse diffraction processes, for example, plane-to-plane transformation, and multiview data recording. The tomographic technique described is analogous to the back-projection and filtering process used in projection tomography and yields high resolution in three dimensions. Results from microwave and ultrasonic image scanners are presented. The ’phase tomogram1 is seen to be, once more, a useful product of this approach and its significance has been investigated by computer simulation.