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 λ/2 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 μm -1 . 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 compare to transient simulations.