Thorkild B. Hansen of Seknion, Inc.

Large antenna arrays have been used widely for decades in radar, imaging, and communications applications. The large number of degrees of freedom attainable with these arrays makes it possible to simultaneously amplify desired signals and filter out undesired signals. This talk discusses two topics related to antenna arrays. The performance of an array improves with its electrical size. Naturally, it would be advantageous if one could reduce the size of an array without degrading its performance. Using Huygens' sources and spherical-harmonics expansions, we revisit this size-reduction problem consisting of finding a smaller source that radiates the field of a larger source. Explicit expressions for Huygens' sources and for the field everywhere outside the smaller source will be derived. The expressions demonstrate that for multi-wavelength sources, a meaningful size reduction will result in prohibitively large field values in the vicinity of the smaller source. Array elements are often spaced half a wavelength apart on a regular grid. For large arrays, this classical array geometry ensures low sidelobe levels and guarantees that no grating lobes will exist. However, in many situations it is beneficial to increase or randomize the element spacing, so that the array becomes sparse. Also, sometimes it is advantageous to use arrays that consist of a number off smaller subarrays. Such non- classical array geometries can be useful if the artifacts they produce (higher sidelobe levels and grating lobes) can be controlled or eliminated. We evaluate some classical and non-classical array geometries in conjunction with both matched-filter and zero-forcing methods.

Biography:

Thorkild B. Hansen received the Ph.D. degree in electromagnetics from the Technical University of Denmark, Lyngby, Denmark, in 1991. He was with the Air Force Research Laboratory (formerly, Rome Laboratory), Hanscom Air Force Base, USA, from 1991 to 1997, where he worked on techniques for analyzing electro- magnetic waves and antennas. He joined Schlumberger's underground radar project in 1997 and transferred with the project to Witten Technologies in 2000.Since 2004 he has worked as an independent consultant in the areas of wave propagation, electromagnetics, antenna theory, arrays, imaging, synthetic aperture radar, and channel models for wireless communication. Also, he is developing techniques for RFID and near-field communications at Seknion, Inc., a company he co-founded. He is co-author of the book Plane-Wave Theory of Time-Domain Fields (IEEE Press, 1999). Dr. Hansen was a recipient of the R.W.P. King Prize in 1992 and the S.A.Schelkunoff Prize in 1995 for publications on electromagnetic wave propagation. The underground radar imaging technology he helped develop at Sclumberger and Witten Technologies won the 2002 NOVA Award for innovation in construction and Wall Street Journal's 2004 Technology Innovation Award in Software.

Thorkild B. Hansen of Seknion, Inc.

Biography:

Thorkild B. Hansen of Seknion, Inc.

Biography:

Thorkild B. Hansen of Seknion, Inc.

Biography: