This paper presents the demonstrator of a fully polarimetric ultra-wideband (UWB) multistatic imaging system for screening of groups of walking people in public areas. The system is working in the FCC UWB frequency band from 3.6 GHz to 10.6 GHz. The low frequency range is chosen to reduce the influence and clutter of clothes to a minimum. This is important for the screening in public places because the scanner needs to identify threats even under thick and heavy jackets with a low false alarm rate. Furthermore, the effect of motion blurring in the reconstructed radar images is enormously reduced. To further improve the detection of threats a fully polarimetric radar frontend was chosen for the imaging system. Radar polarimetry is a well-established technique in remote sensing to characterize di erent scattering mechanisms like single and double bounce or volumetric scattering. This offers the opportunity to classify different terrain properties or manmade objects in remote sensing. The investigated antenna arrangement is a roof-like geometry which can be installed on ceilings or archways in public areas. This approach doesn't disturb the flow of walking persons and even could enable a hidden installation of the screening device. Furthermore, this arrangement reduces shadowing risks, i.e. that a terrorist hides himself between closely walking neighbors. The paper discusses the applied signal processing and the polarimetric evaluation. Results are demonstrated for static and dynamic scenarios.
KEYWORDS: Imaging systems, Antennas, Scanners, Extremely high frequency, Ray tracing, Explosives, Ceramics, 3D metrology, Photography, Information security
Active imaging systems for security screening at the airport or other checkpoints have proven to offer good results. Present
systems require a specific position and posture,13 or a specific movement2 of the passenger in front of the imaging system.
Walk Through Systems (WTS) which screen the passenger while passing the imaging system or a screening hallway would
be more pleasant for the passenger and would result in a great improvement in the throughput. Furthermore the detection
performance could be enhanced since possible threats are visible from different perspectives and could be tracked within
different frames. The combination of all frames is equivalent to a full illumination of the passenger.
This paper presents the concept of a WTS basing on a multistatic imaging system in the mmW range. The benefit is that the
technology of existing portals can we reused and updated to a WTS. First results are demonstrated with an experimental
system.
Active imaging systems in the millimeter wave region have proven to offer good results for security applications. Especially
a coherent signal detection results in a high dynamic range. Several techniques and systems were published in the last
years. The drawback of an active illumination of the measurement object is the effect of shading and poor illuminated
areas due to specular reflections from smooth surfaces. The visibility of an object depends on its surface roughness and
its relative positioning to the imaging sensor. Especially in personnel screening, the human skin behaves as a smooth
mirror for millimeter waves. This paper describes the incorporation of multipath signals in the imaging process to enhance
the illumination properties of active imaging systems. The proposed multipath concept is demonstrated with an active
multistatic imaging system working from 70 to 80 GHz for security applications.
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