Security screening FDTD simulations of the human body and enclosures in polarimetric radar and comparison with measurements

Finite-difference time-domain simulations have been made of a security screening polarimetric radar over the band 18 GHz to 26 GHz, comparing the results with a proof-of-concept system operating over the same band. The proof-of-concept radar is presented together with its calibration and measurement set-up. Measurements indicate the cross-polarisation returns from a human subject are approximately 10 % to 25 % of the co-polarisation returns. A simulation model has been built using the openEMS software to simulate the body of a human, using realistic primitive shapes and electrical properties appropriate for these frequencies, indicating cross-polar returns are in the region of 15 % of the co-polar responses, with the duration of the reflections lasting around 2 ns. The comparisons between the measurements and simulations are good and provide a qualitative understanding of what happens when security screening radar radiation impinges on the human body. The simulation is extended to two simple enclosures, a cubic box and a short cylinder having dimensions of 300 mm and wall thicknesses of 5 mm, which could be made of wood, cardboard, paper or plastic. Results indicate the cross-polar reflection ranges from 3% to 75 % of the co-polar and bursts of reflections are commensurate with reflections from the front and back surfaces, these being separated in time by 2 ns.