Performance Analysis of a Walk-Through Portal Array for Passive Millimeter-Wave 3-D Imaging

The generalized 3-D van Cittert-Zernike (VCZ) theorem highlights the opportunity for short-range passive 3-D imaging as a means of screening the entire human body surface of a walking subject for law enforcement applications. Building on passive millimeter-wave (PMMW) aperture synthesis instrumentation development at Beihang University, the spatial resolution of this technique is shown to be between 5 and 10 mm at the operational frequency of 30 GHz. This is sufficient to recognize the majority of threats likely to be concealed under the clothing of a terrorist or would-be offender. Three architectures of walk-through security screening portals with different antenna arrays are evaluated for this application, these being ones having rectangular, cylindrical, and ellipsoidal geometries. The rectangular antenna array system is downselected as a case study and modeled using a forward and inverse aperture synthesis numerical simulation, presenting experimental data to demonstrate the validity of the beamforming algorithms used. Simulations show that the 3-D spatial resolution within the portal is typically of the order of the radiation wavelength and half a wavelength in the directions, normal and parallel, to the human body surfaces respectively. On the approach to the portal, at the entrance, the spatial resolution falls to a lesser value of twice the wavelength. The possibility of real-time video-rate passive 3-D imaging of the human body using the proposed array is discussed and a route forward is presented to develop demonstrators at Beihang University to realize this next generation of millimeter-wave security screening instruments.