A Complementary Self-Injection-Locked Radar for Low-Power Micrometer-Level THz Sensing and Imaging

This article presents a novel complementary self-injection-locked (CSIL) radar architecture for low-power, high-accuracy THz phase sensing. Unlike conventional phase-sensing radars, the CSIL technique does not require frequency synthesis, enabling a compact architecture with low power consumption. It consists of a coupled oscillator pair with envelope detectors for sensing the oscillation amplitude. The oscillator is connected to a novel on-chip hybrid-mode dual-polarized slot antenna for radiation. The CSIL radar employs the self-injection locking (SIL) technique, where a portion of the transmitted signal reflects off the target and is reinjected into the radar. Due to the coupled nature of the system, this self-injection process induces an amplitude imbalance between the oscillators as a function of the target distance. By measuring this amplitude imbalance using the envelope detectors, the system can estimate relative displacements within an unambiguous range of$\lambda $/4. The CSIL architecture is inherently immune to self-interference. It also features an autodyne design, with a single-phase center, allowing easy integration with external optics such as lenses or mirrors. The proposed radar is fabricated using the TSMC 65-nm process. Operating at 232 GHz, it achieves a static range accuracy of$20~\mu $m while consuming only 4.6 mW of dc power. The architecture also supports 3-D imaging, demonstrated through preliminary imaging experiments. These results establish CSIL as a promising solution for compact, energy-efficient mm-wave and THz sensors in precision sensing and imaging applications.