Near-field millimeter-wave imaging with 77-GHz-band monostatic-radar module

For near-field millimeter-wave (MMW) imaging with high spatial resolution to detect invisible surface cracks with a width of less than 0.2 mm in concrete structures covered with material, we have developed a 77-GHz-band monostatic-radar module containing hybrid integrated radio frequency circuit, direct current and intermediate frequency one, and a guided tapered slot antenna with beam focused in near-field region. An imaging experiment with the module using near-field MMW imaging system based on a raster scanning provides an image with high spatial resolution enough to identify an invisible surface crack with a width of 0.1-mm in a concrete sample even though an image reconstruction technique has not been employed.