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A Two-Dimensional Continuous-Wave Imaging System for Scanning of Dielectric Substrates at Millimeter-Wave Frequencies

This paper presents an RF imaging system capable of performing two-dimensional imaging of planar dielectric substrates at 120 GHz. The proposed system is built around a commercially available radar on chip solution and uses an unmodulated carrier, which greatly simplifies baseband sampling. Image reconstruction is performed by means of an FFT-based backward-wave reconstruction algorithm. We present exemplary imagery of an FR4 sample featuring a copper logo as well as a glass substrate sample featuring a laser-structured ITO coating. The images captured for the two samples allow clear identification of all relevant structures. In addition, we demonstrate that images of satisfying quality can be captured if the system's VCO is operated in free-running mode without an external PLL circuit.