Theoretical and Experimental Characterization of a Near-Field Scanning Microwave (NSMM)

An important aspect to understanding near-field optics and imaging involves the electromagnetic scattering characteristics of objects illuminated by the near field of a sub-wavelength-sized aperture. This paper addresses one particular application of near-field optics: a transmission-mode near-field scanning microscope (NSM). Specifically, some peculiar phenomena are investigated including a near-field focusing effect, as well as an impedance-based image-shape effect. To this end, we first describe the physical attributes of an NSM and then present two computational models we use to characterize this instrument. Both moment-method and f inite-difference t ime-domain models are discussed. These two models are applied to the analysis of the NSM for various configurations and compared to other theoretical and experimental results . Finally, the construction of an X-band NSM is described-which we label a near-field scanning microwave microscope-and the experimental near-field imaging measurements are compared with our numerical predictions.