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The majority of microwave ovens on the market are powered by magnetrons, which can only produce a narrow-band frequency that has a large peak, resulting in poor uniformity. A method is proposed to improve nonuniform heating based on nonlinear response characteristics of the magnetron to produce multi-frequency. First, a multi-physics model of microwave heating is established to realize the calculation of multi-frequency heating. Second, a multi-frequency heating experimental system based on the characteristics of the magnetron is built and verified with the calculated results. The results show that the calculated results are in good agreement with the experimental results. Finally, based on the multi-physics model, the influences of different parameters, such as frequency intervals, cavity size, location of the object to be heated and material properties, on microwave heating uniformity have also been discussed. The results show that the method adopted in this paper is feasible, and the heating uniformity of microwaves is improved. [ABSTRACT FROM AUTHOR]

The influence of anode voltage ripple on injection locking of a magnetron with frequency pushing effect has been studied systematically. Theoretical analysis shows that, when power supply ripple and injection ratio are constant, frequency pushing effect will increase the magnetron's locking bandwidth. Meanwhile, the locking bandwidth decreases with the increase of power supply ripple. Thus, to achieve injection locking, both power supply ripple and frequency pushing effect must be considered. The experiment results show that at injection ratio μ of 0.003, frequency pushing effect at 0.5, and power supply ripple increases from 0% to 1% and 2.5%, the locking bandwidth of magnetron decreases by 0.32 MHz, 2.12 MHz. With the amplitude of ripple increasing, the spectrum after injection locking deteriorates, and output amplitude reduces, which verifies the theoretical analysis. Considering anode voltage ripple and frequency pushing effect, the research results contribute to the realization of high-quality output of injection locked magnetrons. [ABSTRACT FROM AUTHOR]

Magnetron is an important microwave device because of its advantages of high power, small size, lightweight, and low cost. However, due to the instability of magnetron spectrum, it is difficult to use magnetron when we need high-stability spectrum. In order to improve the output spectrum of the magnetron, many efforts have been made and we find that the ripple of magnetron power supply has a great influence on the spectrum. So this article studies this influence systematically. First, we start from the equivalent circuit of magnetron, from which we can derive the equation of high-voltage power supply ripple and magnetron’s time-domain output. Then we obtain the relationship between power supply ripple and magnetron’s frequency-domain output spectrum by fast Fourier transform. Through theoretical derivation, numerical simulation analysis and experiment, we find that with the increase of ripple, the spectrum is gradually disordered, noise frequency point appears, center frequency point remains unchanged, and output energy reduces. The research results of this article provide theoretical guidance for the realization of high-stability spectrum magnetron. [ABSTRACT FROM AUTHOR]

A microwave power-combining technique based on magnetrons has been widely researched to solve the urgent demands for high-power, low-cost microwave sources in microwave industrial applications. To achieve high resultant efficiency, conventionally, injection locking with static frequency is utilized to drag the output frequency of each magnetron source to the exact same frequency, and a phase shifter is required to adjust the output phase of each combining source. In this article, we propose a novel phase shifterless microwave power system with two magnetrons utilizing a frequency-searching injection-locking technique. Coaxial cables with different physical lengths are used to realize phase adjustment under different injection frequencies. By sweeping the injection frequency in a small band, the phase difference between combining signals can be adjusted. Thus, high resultant efficiency can be obtained. When the injection frequency is swept, the phase difference between the output and injection signals has been analyzed theoretically, the phase difference between the different-length coaxial injection cables has also been analyzed. Furthermore, the relationship between the sweeping frequency bandwidth and requirements of the minimum length difference of the coaxial injection cables has been derived and analyzed. Experimental results show that a high resultant efficiency of 94.6% can be obtained with the proposed phase shifterless system. The system could maintain high resultant efficiency even when the free-running frequency and power of one magnetron are changed by adjusting its anode current. The experiments reveal that the proposed method works for different combining sources. [ABSTRACT FROM AUTHOR]

Jamming signals are usually generated by solid-state microwave sources that are high in cost, low in efficiency, and fragile. In this article, we present a novel approach in which a high-power jamming signal is generated from a continuous-wave magnetron in a low-cost and highly efficient way. The remote-control communication signal of an unmanned aerial vehicle (UAV) is successfully jammed by a magnetron jamming transmitter working around 5.8 GHz. The UAV uses the frequency-hopping binary phase shift keying (FH-BPSK) technique for communication. The magnetron jamming transmitter can adjust its output power and spectrum (which have a strong relation to the jamming results) by changing its anode current. The calculation of the bit error ratio (BER) of FH-BPSK communication under the jamming signal from the magnetron is derived theoretically. Then, the variation of BER under different anode currents of the magnetron and different distances between the UAV and its remote controller are analyzed. The comparison of experimental results and theoretical analysis show that the UAV is successfully jammed when the BER is higher than 6%. Because the distance between the UAV and its remote controller is fixed at 26 m, jamming succeeds when the anode current of the magnetron is between 70 and 120 mA. If the anode current of the magnetron is fixed, jamming could also succeed with a greater distance between the UAV and its remote controller. [ABSTRACT FROM AUTHOR]

Currently, microwave energy is utilized for many diverse industrial applications because of its various advantages including its eco-friendliness. Low-cost, high-efficiency, and high-power industrial microwave sources are in urgent demand. In this paper, we propose a low-cost quasi-coherent power-combining system based on a combination of two magnetrons. We have analyzed and built a low-loss waveguide-based applicator combined with specific phase. This system utilizes the coupling of the combiner to quasi-lock the slave magnetron. A waveguide phase shifter lies in the slave magnetron branch to adjust the phase difference between the master and slave magnetrons’ signals to achieve high resultant efficiency. Based on theory, the phase difference between the master and the injected slave magnetrons has been numerically calculated and analyzed. The phase difference changes periodically when the slave magnetron is quasi-locked to the master magnetron and the periodicity increases with the injection ratio. Experimental results show the resultant efficiency of the proposed system can reach as high as 92% when using several suitable waveguide components. The investigation also provides guidelines for further microwave power combination systems with multiple sources. [ABSTRACT FROM PUBLISHER]