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W-band speckle contrast measurements with a Hadamard diffuser Host Publication: Finds and Results from the Swedish Cyprus Expedition: A Gender Perspective at the Medelhavsmuseet Authors: I. Jäger, J. Stiens, G. Koers, S. Islam and R. Vounckx Publication Date: Sep. 2006 Number of Pages: 6
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 image pixel into a sum of intensities (noncoherent). We report a 50% speckle reduction. The effect of speckle reduction was measured using a W band free space scalar calibrated measurement setup. The setup makes it possible to accurately measure the reflection of material samples or surfaces by means of a novel scalar calibration technique using only amplitude detection and two measurements per frequency. We processed 2 different Hadamard diffusers and present here measurement data discussing speckle contrast as a function of frequency. External Link.
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