An in-depth investigation of the global behavior of wireless injection-locked oscillator circuits is presented. This kind of operation has been proposed for motion-sensing applications, in which each oscillator is also self-injection locked by the signal reflected by the target, with the overall system behaving in an autonomous manner. The analysis is based on a realistic description of the effect of the self-injection and mutual-injection signals, and the oscillator behavior, described with a reduced-order model, extracted from harmonic balance. As will be shown, sinusoidal dependences on the oscillation frequency, associated with the signal propagation, may give rise to turning points in the solution curves, whereas the mutual synchronization of the oscillator circuits inherently gives rise to a coexistence of solutions with different phase shifts. The investigation includes fundamental aspects such as the bifurcation phenomena and phase-noise variation with the distance and antenna gain. The aim is to develop a useful methodology for the efficient analysis and reliable prediction of the behavior of these promising systems. All the results obtained with the new formulation, for easy application, have been carefully validated with costly circuit-level simulations of the whole system. For experimental validation, a prototype operating at 2.45 GHz has been manufactured and measured.

This work was supported by the Spanish Ministry of Economy and Competitiveness under the research project TEC2014-60283-C3-1-R and Juan de la Cierva Research Program IJCI-2014-19141 and by the Parliament of Cantabria under the project Cantabria Explora 12.JP02.64069.