The Effects of Obscuration in Passive 3-D Millimeter-Wave Imaging for Human Security Screening

The possibility of near-field passive 3-D imaging using the aperture synthesis technique is theoretically proven and highlights the opportunity for imaging the entire human body by an antenna receiving array that surrounds the body. In these scenarios there will be partial obscuration of some regions of the body, by other parts of the body. This results in some receivers in the array being able to measure emission from certain parts of the body, while others are obscured from a measurement. A model is presented which enables the effects of obscuration to be assessed for planar-like, cylindrical-like, and concave-like regions of the human body. The effect the obscuration has on the spatial resolution of the imager is evaluated by examining the 3-D point spread function, as determined by a near-field aperture synthesis imaging algorithm. It is shown that over many areas of the human body, the Abbe microscope resolution of gimel/2 (5mm@30GHz) in a direction transverse to the human body surface is achievable, an attractive proposition for security screening. However, the spatial resolution in a direction normal to the human body surface is shown to be close to gimel (10mm@30GHz). In regions of greater obscuration, such as in the armpits, the resolution may fall to gimel (10mm@30GHz) and 5 gimel (50mm@30GHz) in the directions transverse and normal to the human body surface, respectively. It is also shown by simulation using a human body solid model and the 3-D aperture synthesis imaging algorithm how the image quality changes with the number of receiving antennas.