Improving the quality of active millimeter wave standoff imaging by incorporating the cross-polarized scattering wave.

In this paper, we study the feasibility of incorporating the cross-polarized scattered wave in active standoff millimeter-wave imaging in order to improve the edge detection and background suppression for metallic objects. By analyzing the scattering from a perfectly conducting (PEC) patch of a simple geometrical shape we show that the edge diffraction is the major source of cross-polarized scattering. A similar scattering behavior is also observed for a PEC patch placed on a dielectric medium. Hence, the cross-polarized scattered field conveys valuable information about the edges of the object. In addition, the cross-polarized scattering can be utilized to resolve the object from an unstructured reflective background. To put these ideas to the test, a standoff imaging system composed of a continuous-wave (CW) semiconductor source, a focal plane array detector (camera), and collimating and objective lenses at 95 GHz is utilized to image the co- and cross-polarized reflection from metallic patches both in the presence and in the absence of a background medium. In agreement with theory, the experiments reveal that the edges of the object can be enhanced and reflections from a smooth background medium can be suppressed by using the cross-polarized scattering. In this regard, the conducted experiments on the metallic patches placed on the human body also yield promising results.