Coherent optical beam forming with passive millimeter-wave arrays

Passive millimeter-wave imaging requires large apertures to achieve an angular resolution comparable to that of typical infrared imagers. Aperture synthesis offers a route to achieving high resolution without using a single large aperture, by interferometrically combining the signals from a number of smaller distributed apertures. In such a system the individual millimeter-wave signals must be transported to a common location with good phase fidelity and combined to form the image. This paper discusses a technique called coherent optical beam forming which performs optical transport of the up-converted millimeter-wave signal and direct image formation at the optical frequency. Proof of principle experiments are described that demonstrate coherent optical beam forming with a point source and a method of self-calibrating the array to remove phase errors.