Millimeter-wave interferometric sensor for surface profiling

Interferometry is an attractive technique for characterizing surface profiles due to its high measurement accuracy and fast operation. Particularly, it can resolve a range within a half-wavelength of the operating frequency. Optical interferometers (Sommargren, 1981) have been developed to map optical components, such as lens, with very high sensitivity in the order of 1 Å. Fast and accurate surface-profiling systems are needed for the evaluation of quality of surfaces in various engineering applications. We report, for the first time, a millimeter-wave interferometric surface-profiling sensor prototype operating at 35 GHz for one-dimensional surface mapping. The system was fabricated using both microwave integrated circuits (MIC) and microwave monolithic integrated circuits (MMIC). It is capable of measuring accurately the surface topography of metal contours with sub-millimeter resolution and accuracy.