Complex Permittivity Extraction From Synthetic Aperture Radar Images

Abstract

Microwave and millimeter wave synthetic aperture radar (SAR) imaging techniques are commonly used to generate high-resolution qualitative images showing the reflectivity (or complex permittivity) contrast in a sample-under-test (SUT). These techniques have been successfully applied for many diverse applications. However, these images lack quantitative information about the SUT, namely; its complex permittivity distribution. In this article, a novel method to extract the spatial distribution of complex permittivity from SAR images is proposed. The principle of the proposed method is outlined, then verified by a series of electromagnetic simulations, demonstrating that the proposed method can accurately extract the complex permittivity. Additionally, it is shown that the results are robust with respect to most critical parameters of the SAR imaging technique. Subsequently, measurements were performed to verify the efficacy of the proposed method on two SUTs with different complex permittivities, corroborating the utility of the proposed method. Moreover, the measurement results of one of the SUTs showed that the proposed method is capable of detecting local inhomogeneities with a relatively high spatial resolution. Then, an SUT with artificial defect was prepared to investigate this capability. Compared to quantitative methods based on inverse scattering techniques, this proposed method requires much less computational resources and has the potential for becoming an effective material characterization technique in the nondestructive evaluation (NDE) field.