High-Resolution Microwave Near-Field Surface Imaging Using Resonance Probes

A novel microwave high-resolution near-field imaging technique is proposed and experimentally evaluated in reflectometry imaging scenarios involving planar metal-dielectric structures. Two types of resonance near field probes-a small helix antenna and a loaded subwavelength slot aperture are studied in this paper. These probes enable very tight spatial field localization with the full width at half maximum around one tenth of a wavelength, λ, at λ/100-λ/10 standoff distance. Importantly, the proposed probes permit resonance electromagnetic coupling to dielectric or printed conductive patterns, which leads to the possibility of very high raw image resolution with imaged feature-to-background contrast greater than 10-dB amplitude and 50° phase. In addition, high-resolution characterization of target geometries based on the cross correlation image processing technique is proposed and assessed using experimental data. It is shown that printed elements features with subwavelength size ~λ/15 or smaller can be characterized with at least 10-dB resolution contrast.