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Proceedings Paper

W-band speckle contrast measurements with a Hadamard diffuser
Author(s): Irina Jaeger; Johan Stiens; Gaetan Koers; Saiful Islam; Roger Vounckx
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Paper Abstract

Millimeter waves are able to penetrate materials that are usually opaque to both visible and infrared radiation. We used this advantage to design a free-space active millimeter-wave imaging set up for security applications. Because all existing mm-wave sources are coherent - speckle is one of the ultimate limiting factors of the imaging techniques. This problem is of special importance for mm-wave imaging, because surface roughness is closer to the object dimension as in optical imaging. The reduction of speckle is highly desirable and we propose here a Hadamard matrix solution, which is one of the most efficient ways to reduce speckle noise. By illuminating the object with a series of orthogonal phase patterns corresponding to permutations of Hadamard matrices, one can convert the sum of electrical fields (coherent) in the image pixel into a sum of intensities (non-coherent). We report a 50% speckle reduction. The effect of speckle reduction was measured using both a vector network analyzer and a W-band free-space scalar calibrated measurement setup. We processed 2 different Hadamard diffusers and present here measurement data discussing speckle contrast as a function of frequency.

Paper Details

Date Published: 15 September 2006
PDF: 6 pages
Proc. SPIE 6341, Speckle06: Speckles, From Grains to Flowers, 634103 (15 September 2006); doi: 10.1117/12.695253
Show Author Affiliations
Irina Jaeger, Vrije Univ. Brussel (Belgium)
Johan Stiens, Vrije Univ. Brussel (Belgium)
Gaetan Koers, Vrije Univ. Brussel (Belgium)
Saiful Islam, Vrije Univ. Brussel (Belgium)
Roger Vounckx, Vrije Univ. Brussel (Belgium)

Published in SPIE Proceedings Vol. 6341:
Speckle06: Speckles, From Grains to Flowers
Pierre Slangen; Christine Cerruti, Editor(s)

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