A 0.55-THz Self-Injection-Locked Resonant Tunneling Diode Radar for Micrometer Ranging

This work presents self injection-locked (SIL) continuous-wave (cw) radar sensors based on resonant tunneling diode (RTD) oscillators. The free-running RTD oscillators show micrometer resolution in sampling the movement of a reflective target. The SIL device utilized a sawtooth-like frequency modulation with <tex-math notation="LaTeX">λ /2 </tex-math> periodicity induced by time-delayed feedback, which is used for unambiguous ranging. The maximum frequency shift achieved herein is 5.5 GHz, whereby a frequency shift of about 1 GHz is used in operation. The achieved sensitivity of the SIL radar during operation is 9.2 MHz <tex-math notation="LaTeX">μ </tex-math>m <tex-math notation="LaTeX">^-1 </tex-math>. We also propose a method for determining the absolute distance to the target based on the SIL frequency modulation mechanism as a proof of concept. Using a simplified circuit model for the RTD SIL radar, we convert the corresponding delay-differential equation to an approximate dynamic amplitude-phase system, to give an envelope description for the SIL radar of reduced stiffness compared to transient simulations.