Aperture synthesis for passive millimetre wave imaging provides a means to screen people for concealed threats in the extreme near-field configuration of a walk-through portal; a regime where the imager to subject distance is of the order of both the required depth-of-field and the field-of-view. As shown here, the field-of-view in these scenarios is unlimited and the spatial resolution is slightly better than the half-wavelength Abbe microscope resolution. As in this scenario the subject would be surrounded by receiving antennas, all surfaces of the human body will be in focus with high-resolution, even at the low frequencies. For example at a frequency of 22.51 GHz the spatial resolution is in the region of ~ 7 mm. This capability is ideally suited to the aircraft security screening industry. Furthermore, the aperture synthesis imager is well suited to non-cooperate screening at longer ranges, as the antenna arrays may be deployed on almost any available surface. The field-of-view of these systems is likewise unlimited, extending from the near-field to the far-field. The spatial resolution of these systems, as here shown, is in the region of the half-wavelength resolution close to the imager, and slightly better than the Fraunhofer diffraction resolution limit at longer ranges. Therefore, also for the non-cooperate screening scenarios, the subject will always be in focus with the best possible spatial resolution allowed by the physics of imaging.
Neil A. Salmon, "Spatial resolutions and field-of-views in millimetre wave aperture synthesis security screening imagers," Proc. SPIE 10800, Millimetre Wave and Terahertz Sensors and Technology XI, 1080004 (Presented at SPIE Security + Defence: September 10, 2018; Published: 5 October 2018); https://doi.org/10.1117/12.2502925.
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