A 0.28 THz Super-Harmonic Self-Injection-Locked Radar for Vibration Sensing and Phase Imaging

This letter presents a continuous-wave (CW) radar for micrometer-level phase and vibration detection based on super-harmonic self-injection locking in a free-running oscillator. The radar system consists of an oscillator that radiates a signal which gets reflected off a target. The reflected signal is re-injected into the oscillator. Due to super-harmoinc self-injection-locked (SSIL), this causes a frequency shift dependent on the target distance, enabling precise ranging. The proposed radar is implemented using a 140 GHz oscillator followed by an efficient medium-breakdown HBT-based doubler and on-chip antenna. The doubler achieves a peak EIRP of +25.3 and −0.1 dBm radiated power at 281 GHz and consumes 144 mW dc power (dc-to-THz efficiency of 0.68%). In SSIL radar operation, a frequency shift of 250 MHz is observed. Using the proposed radar, we demonstrate: 1) detection of sub- $30~\mu $ m vibrations and 2) reflection-based phase imaging.