W-band speckle contrast measurements with a Hadamard diffuser

Irina Jaeger; Johan Stiens; Gaetan Koers; Saiful Islam; Roger Vounckx

doi:10.1117/12.695253

15 September 2006 W-band speckle contrast measurements with a Hadamard diffuser

Irina Jaeger, Johan Stiens, Gaetan Koers, Saiful Islam, Roger Vounckx

Proceedings Volume 6341, Speckle06: Speckles, From Grains to Flowers; 634103 (2006) https://doi.org/10.1117/12.695253
Event: Speckle06: Speckles, From Grains to Flowers, 2006, Nimes, France

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.

Citation Download Citation

Irina Jaeger, Johan Stiens, Gaetan Koers, Saiful Islam, and Roger Vounckx "W-band speckle contrast measurements with a Hadamard diffuser", Proc. SPIE 6341, Speckle06: Speckles, From Grains to Flowers, 634103 (15 September 2006); https://doi.org/10.1117/12.695253

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