Broadband Microwave Near-Field Imaging by Localized Field Perturbations

Inverted scanning microwave microscopy (iSMM), as a novel near-field characterization tool, demonstrates unique advantages in research fields such as biomedicine and the dielectric properties of two-dimensional materials. This paper proposes a dual-port inverted scanning imaging method based on the perturbation of the spatial microwave field in microstrip lines by an uncoated silicon tip. Combining microwave vector network analysis techniques, a non-invasive silicon tip scans the surface of samples above the microstrip line to obtain local S₁₁ and S₂₁ scattering parameters. Theoretical modeling and experiments validate the broadband resonant characteristics of the microstrip structure across the 1-10 GHz frequency range. Near-field images of dried mouse fibroblasts were successfully acquired at selected frequencies (3, 5, and 8 GHz), revealing their distinct electromagnetic responses at different frequencies. Comparison of the signal-to-noise ratios (SNR) for S₁₁ and S₂₁ parameters indicates that the S₂₁ SNR exhibits more stable fluctuations (30-60 dB) across the 1-10 GHz range. This testing method possesses broadband microwave imaging capabilities, providing a reliable technical foundation for structural characterization studies in fields such as microelectronic devices, biological tissues, and functional materials.