Coherence Reduction of the Measurement Matrix in Microwave Computational Imaging by Introducing Polarization Diversity

Abstract

For microwave computational imaging (MCI), the reduction of measurement matrix's coherences permits better reconstruction performance. Therefore, frequency diverse apertures (FDAs) have become a major option of antennas for MCI due to thier frequency-varying radiation patterns. The frequency diversity in the patterns reduces coherences; however, the losses in practical materials and the finite sizes of apertures impose upper limits on frequency diversity. For further coherence reduction, the polarization diversity (PD) of aperture elements is as a new approach introduced in this paper. We present an electromagnetic formulation of scattering aperture elements' PD. In the formulation, the PD brings an additional degree of freedom in the generation of the measurement matrix, given the apertures being illuminated with varying polarizations. This new degree of freedom enables a potential of reducing the coherences. Two complementary electric-field-coupled (cELC) scattering apertures, which differentiate in the polarizations of elements, are fabricated for validation. A set of comparisons yielded by the near-field scanning data of these apertures shows that the PD effectively reduces coherences and improves reconstruction performance.