Circularly polarized imaging for passive millimeter-wave security screening

Passive millimeter-wave imaging has been demonstrated to detect a wide variety of hidden objects. Polarimetric imaging can obtain much more information about observing scenes. Some works have reported polarimetric imaging simulations and multiple linear polarization imaging experiments. However, there is no work reporting the independently circular polarization imaging experiments of indoor body security inspection scenes. In this paper, we have constructed an imaging system, which can generate circular polarization images. The imaging system mainly contains two circular polarization antennas, a W-band radiometer, a focal plane lens, an arcshaped orbit for horizontal pixel, a plane reflector for vertical pixel, and a control computer. The radiometer is placed on the base of the arc-shaped orbit. By putting a left-hand or right-hand circularly polarized antenna on the flange of the radiometer, we can acquire the corresponding left-hand or right-hand circular polarization image. Circular polarization imaging experiments of several human security screening scenarios have been conducted and polarization characteristics have been analyzed. The experimental results indicate that circular polarization imaging can obtain different information from linear polarization imaging and can be helpful to improve image quality.