† Corresponding author. E-mail:
Project supported by the National Basic Research Program of China (Grant No. 2013CB328902) and the National Natural Science Foundation of China (Grant No. 61501311).
A microwave power-combining system composed of two Panasonic 2M244-M1 magnetrons based on master–slave injection-locking is demonstrated in this paper. The principle of master–slave injection-locking and the locking condition are theoretical analyzed. Experimental results are consistent with the theoretical analysis and the experimental combined efficiency is higher than 96%. Compared with the external-injection-locked system, the power-combining based on the master–slave injection-locking magnetron is superior by taking out the external solid-state driver and the real-time phase control system. Thus, this power-combining system has great potential for obtaining a high efficiency, high stability, low cost, and high power microwave source.
High power microwave source is urgently needed in a variety of areas such as environmental engineering,[1,2] nanostructures pyrolysis,[3] plasma heating,[4,5] and material processing.[6,7] In particular, the solar power satellite (SPS) is hotly discussed as a result of transferring solar energy to Earth using microwaves.[8] Magnetron whose efficiency routinely exceeds 80% and unit cost less than 7 $ is very suitable for these applications.[9,10] However, magnetron has some drawbacks such as the power capacity limit for one magnetron, wide-band output, unstable frequency and uncontrolled phase which make it difficult to directly apply in large-scale industrial applications.[11] To solve these problems, an alternative way is power-combining. Dutch physicist Christiaan Huygens observed the synchronization behavior of two closely hung pendulum wall clocks in 1665 which inspired people to study locking phenomena,[12] Adler found the locking condition of phase locking oscillators in 1940s.[13] Benford and Woo used a short waveguide to connect two magnetrons and obtained phase locking in their peer-to-peer locking system in 1988.[14] Peer-to-peer phase locking of magnetrons provides a new method which uses the coupling between the magnetrons instead of external signals. However, a large amount of couplings are required in a multiple-magnetron system with the peer-to-peer locking method, so the system is difficult to be applied for large-scale power combining.[15] Power combining based on the external-injection-locked magnetron has been proposed. The system is very complex and expensive because every magnetron needs an external solid-state driver and a central control system should be provided to adjust the phase difference of the magnetrons.
In this work, we propose a power-combining system based on the master–slave injection-locking magnetron. Compared with the previous systems, this system does not need an external solid-state driver or a real-time phase adjustment system, and the combined efficiency reaches as higher as 96%. This method provides a solution for a high power, low cost microwave source.
Figure
![](cpb_25_7_078402/cpb160251ieqn1.gif)
Circuit model of a locked magnetron.
When the master magnetron and the slave magnetron satisfy Eq. (
Figure
The practical configuration of this power-combining system is depicted in Fig.
The master magnetron oscillates at around 2.4512 GHz. With the anode current altering from 240 mA to 280 mA, the injection power changes from 0 W to 50 W. Meanwhile the power-combining source power from the master magnetron varies from 903 W to 765 W. The slave magnetron oscillates at its free-running frequency with the anode current altering from 320 mA to 280 mA so that the two sources can stay at the same power level. At the beginning of the experiment, we manually adjust the phase shifter to 135° (with which this system can obtain the highest efficiency) and keep the phase steady till the end of the experiment. As shown in Fig.
In order to confirm the relationship between the phase and the power-combining efficiency, we first adjust the attenuator and the anode current to the state with which the injecting power is around 53 W (the slave magnetron can be locked with the master magnetron) and the source power from the master magnetron is around 780 W. The slave magnetron output is around 800 W in Fig.
![]() | Table 1. Combined efficiency with different phase difference. . |
Noting that the master magnetron output and the injection power are 830 W and 50 W respectively, we measure the power-combining output power with different power of the slave magnetron to analyze how the sources power difference affects the combined efficiency. The anode current of the slave magnetron is adjusted from 160 mA to 340 mA in Fig.
Microwave power-combining of two Panasonic 2M244-M1 magnetrons based on a master–slave injection-locking system has been developed and studied in this paper. Experimental results show that the slaver magnetron output can completely follow the master magnetron output. The combined efficiency increases with the decrease of the phase difference and the sources power difference, and the combined efficiency is as high as 96.2%. This power-combining system is simple and less cost without the external solid-state driver and the real-time phase adjustment system. This method has great potential in developing a high power source which is cheaper and more convenient. In addition, this method provides a foundation for the power-combining based on one master and multiple slave magnetrons which will be studied in the future.
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