Analysis of self-injection locked oscillators for motion sensing applications

Self-injection locked oscillators have been recently proposed for motion sensing applications demonstrating a good experimental performance. Here a detailed investigation of the system dynamics is presented using a realistic model of the oscillator circuit under the injection of the reflected signal, which is phase modulated due to the target motion. The instability effects observed for some distance values are studied by means of a perturbation method and the results are validated through comparison with full circuit-level simulations and with measurements. The regular operation ranges are efficiently determined through a bifurcation analysis in terms of the distance to the target and the antenna gain. The modulation effect is analyzed with a reduced-order envelope transient formulation that copes with the accuracy problems associated with the small values of the modulation frequency. Very good agreement has been obtained with the experimental results.