A Two-Sided, Reflection-Based K-Band 3-D Millimeter-Wave Imaging System With Image Beat Pattern Mitigation

Abstract

Active millimeter-wave (mmWave) imaging illuminates a scene with a source of mmWave energy and forms images based on the reflected energy. When imaging objects (such as packaged goods in commerce) that have a mixture of opaque and translucent parts, two-sided reflection imaging can be used to overcome the occlusion by the opaque objects that would plague a transmission imaging approach. However, the two-sided reflection imaging approach suffers from wavelength-dependent beat patterns when coherently combining the images from each side. We present and experimentally verify an approach to successfully mitigate this image beat pattern. The presented two-sided <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> -band 3-D mmWave imaging system achieves system resolutions of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\delta }\text {x} = 17.07$ </tex-math></inline-formula> mm, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\delta }\text {y} = 4.62$ </tex-math></inline-formula> mm, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\delta }\text {z} = 7.26$ </tex-math></inline-formula> mm, with an accuracy of 0.8 mm in the y- and z-directions. It is shown that the system is not only capable of producing beat-pattern-free 3-D images of the products inside an optically opaque corrugated cardboard shipping box but also the two-sided approach with image beat pattern correction showing an increased image volume even if portions of the scene are occluded.