The Bifocal Microwave Microscope

Millimeter-wave imaging radar is becoming increasingly popular for sensing and security applications. Usually full phased arrays, synthetic apertures, or focusing reflect-arrays are employed to sense a given image space. One new approach is to generate an axially-scanning focal spot using an axial nearfield bifocal dual reflector. The bifocal has two perfect foci on the symmetry axis, each corresponding to the two perfect feed points on the axis, made possible when two degrees of freedom – two reflectors – are employed. With two perfect foci, the optical aberrations for other image points between them must be of even order, which leads to a reasonable focal region bounded by the perfect foci. It is envisioned that a small feed moving along the axis might interrogate the image region, with better precision and speed, and less force than the full focusing stage. Alternatively, an electronically selective line source could scan the image space at nanosecond rates using only one dimension of sensing hardware. The concept is referred to as a microscope, because it maps rays diverging from the image space to rays converging at the observation points much like an optical microscope.