PNNL

Abstract

This paper describes a study performed at the Pacific Northwest National Laboratory investigating the use of active millimeter-wave radar imaging to perform threat detection in non-divested shoes. The purpose of this study was to determine the optimal imaging system configuration for performing this type of task. While active millimeter-wave imaging systems have proven to be effective for personnel screening, the phenomenology associated with imaging within a heterogeneous medium, such as a shoe, dictates limits for imaging system parameters. Scattering, defocusing, and multipath artifacts are significantly exaggerated due to the high contrast index of refraction associated with the boundary at the air and shoe interface. Where higher center-frequency and bandwidth result in much improved lateral and range resolution in the body scanning application, smaller wavelengths are significantly defocused after penetrating the sole of the shoe. Increased bandwidth, however, is essential for the shoe scanning application as well. Obtaining fine enough depth resolution is critical in separating the scattering contribution of each layer of the shoes in range to isolate possible threats embedded within the sole. In this paper the results of this study covering the optimization of the following imaging system parameters is presented: antenna illumination beamwidth, antenna polarization, transceiver bandwidth, and physical scanning geometry.