High-resolution 3D Microwave Imaging Using an Optically Tracked Linear Array

Active three-dimensional (3D) microwave and millimeter-wave imaging techniques have been extensively developed for concealed threat detection at the Pacific Northwest National Laboratory (PNNL), most notably the cylindrical millimeterwave imaging method currently in use for airport screening. Typically, a linear array is mechanically scanned over a cylindrical or planar aperture in order to form a high-resolution 3D image. A linear array mounted on a low-cost encoderdriven rail system was desired for rapid data collection and evaluation of concealed threat detection on a stationary target. A rail system to sweep out a planar aperture was quickly developed, however, due to the low-cost implementation of the rail system and encoder, resulting images were lower quality than expected. It was determined that the position information provided by the rail system encoder was not accurate enough to generate an image of the desired quality. Instead of using a traditional encoder wheel with the rail system, optical motion tracking was used to record 3D position information of the linear array synced with the radar as it was manually scanned over a nominally planar aperture. While optical motion tracking can provide position information with sub-millimeter level accuracy, it doesn’t guarantee that the scanned aperture is strictly planar or uniformly sampled. Reconstruction techniques necessary to incorporate 3D position information and compensate for an irregular imaging aperture are developed. Experimental results showing the benefit of precise optical motion tracking for a manually scanned linear array are presented.