Detection of Metal Edge orientation in Near-Field Imaging Using Higher-Order Mode Coupling

A planar metallic pattern, such as one of a circuit board, is imaged contactless by two-dimensionally scanning the pattern plane with a probe-to-probe transmission measurement system. The distance between the probe tips is about a quarter wavelength, allowing for the use of higher-order mode evanescent fields for the transmission. Coupling of linearly polarized field modes to the circularly-symmetrical higher-order TM
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mode is dependent on the orientation of the metallic edge at a specific spot of the imaged pattern, allowing for the detection of edge orientation by a single-pixel measurement. The concept is experimentally demonstrated at 31 GHz with subwavelength resolution of metallic features.