Magnetrons are widely used in microwave-based industrial applications, which are rapidly developing. However, the coupling between their output frequency and power as well as their wideband spectra restricts their further application. In this work, the output frequency and power of a magnetron are decoupled by self-injection. Moreover, the spectral bandwidth is narrowed, and the phase noise is reduced for most loop phase values. In order to predict the frequency variation with loop phase and injection ratio, a theoretical model based on a circuit equivalent to the magnetron is developed. Furthermore,the developed model also shows that the self-injection magnetron is stabler than the free-running magnetron and that the magnetron’s phase noise can be reduced significantly for most loop phase values. Experimental results confirm the conclusions obtained using the proposed model. However, the coupling between their output frequency and power as well as their wideband spectra restricts their further application. In this work, the output frequency and power of a magnetron are decoupled by self-injection. Furthermore, the spectral bandwidth is narrowed, and the phase noise is reduced for most loop phase values. a frequency model with a loop phase and injection ratio, a theoretical model based on a circuit equivalent to the The developed model also shows that the self-injection magnetron is stabler than the free-running magnetron and that the the magnetron’s phase noise can be reduced significantly for most loop phase values. Experimental results confirm the conclusions obtained using the proposed model.