2.4-GHz-Band High-Power and High-Efficiency Solid-State Injection-Locked Oscillator

There is increasing research interest in the development of solid-state devices to provide intelligent uniform heating, spot heating, and so on. However, the use of the solid-state devices to realize the same 1-kW output power as a conventional microwave oven requires configuration complexity that, for the moment, prevents its wider adoption. Although there is a demand for microwave generators with average output power of several tens to several hundreds of watts, existing solid-state solutions cannot produce this level of power. These problems prompted us to investigate, both by analysis and prototyping, small injection-locked oscillators that use high-efficiency microwave generators to provide several hundred watts of output power. Using an imbalanced coupling resonator in the feedback circuit, we were able to achieve an output power of 210 W and an efficiency of 51% at 2.45 GHz, when injecting a reference signal at a level of less than 1/10 000 of the output power. The high-power and high-efficiency solid-state injection-locked oscillators described in this paper have the advantages of long life, tunable frequency and phase, and low-voltage operation. These characteristics are potentially useful for realizing precise temperature control in chemical reactions, as well as spot and uniform heating by microwave ovens.