Sensitivity and Distortion Analysis of a 125-GHz Interferometry Radar for Submicrometer Motion Sensing Applications

In all quadrature direct-conversion receivers, signal deterioration due to $I/Q$ mismatch may happen, causing a mirrored signal to appear superimposed onto the desired signal, thereby destroying the orthogonality of the demodulated signal. This effect strongly affects radar systems over 100 GHz, since they are sensitive to small fabrication errors. In addition, when slow movements are measured with ac-coupled interferometric radars, coupling distortions are observed. In this article, these distortions were analyzed for interferometric radars and then resolved using a novel phase imbalance correction method for a 125-GHz radar. The effectiveness of the proposed solution was verified experimentally for speech information sensing and for small motion detection applications. By successfully measuring a 95-nm sinusoidal movement, the high sensitivity of millimeter-wave (mm-wave) radars was demonstrated. Moreover, noise analyses for small-motion interferometry radars have been presented and a model for sensitivity estimation was proposed.

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