University of Delaware - College of Engineering

Dennis Prather, Engineering Alumni Professor

Passive Millimeter-wave Imaging

On a collective level, we use an array of integrated devices (all fabricated in our lab) and components to realize a fully integrated millimeter-wave (mmW) imaging system that offers the unique ability to penetrate many visual obscurants without utilizing harmful ionizing radiation. From security checkpoints to the ability to see in degraded visual environments, there are many potential applications for such imaging systems. However, the widespread implementation of these imagers has been limited due to size and weight constraints. At these wavelengths, the diffraction limit imposes large apertures on the order of 0.5 meters to achieve reasonable resolutions for most applications. The volumetric scaling associated with traditional imaging optics thus largely precludes the realization of such imagers with practical form factors.

In our work, we have developed ‘passive’ (meaning no illumination) mmW imagers that utilize a distributed array of antennas at the aperture plane. Energy captured by these antennas is then converted to optical wavelengths using high-frequency optical modulators, routed via lightweight optical fibers, and reimaged through a central optical processor onto a simple optical camera. Using this technique, we have been able to realize video-rate, passive mmW imaging at 75 GHz with no moving parts. This imager has direct relevance to many civilian and defense applications and has already been tested against worst-case helicopter brownout conditions and imaging through heavy fog. Additionally, with minor modifications, this distributed aperture imager could be adapted to perform microwave and mmW source geolocation and identification for electronic warfare or MIMO communications.

Recent publications

C. A. Schuetz, D. W. Prather, et al., "Realization of a Video-Rate Distributed Aperture Millimeter-wave Imaging System using Optical Upconversion," in SPIE Passive and Active Millimeter Wave Imaging XVI, Baltimore, MD USA, 2013, p. 87150I.

J. P. Wilson, C. A. Schuetz, T. E. Dillon, R. D. Martin, and D. W. Prather, "Polarimetric passive millimeter-wave imagery from a sensor based on an optical up-conversion architecture," in SPIE Passive and Active Millimeter Wave Imaging XV, Baltimore, MD USA, 2012, p. 83620A.

C. A. Schuetz, J. Murakowski, G. J. Schneider, and D. W. Prather, "Radiometric millimeter-wave detection via optical upconversion and carrier suppression," IEEE Transactions on Microwave Theory and Techniques, vol. 53, pp. 1732-1738, 2005.

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