| It has become clear that conventional magnetrons do not operate effectively in the millimeter-wave band because of some main limitations,which are inherent in their design.First,the dimension of cavity becomes too small to fabricate with the increasing of frequency since they scale as ?(the wavelength).Second,the DC magnetic field grows as 1/?.Third,with the scale of cathode decreasing,the necessary current density and back bombarding are so intense that the lifetime of thermionic cathodes is too short from the practical applications.Last,the method of achieving ? mode voltage separation by the use of straps has approach its technological limit.Therefore,several solutions have been proposed to overcome these problems and to develop effective M-type devices in the millimeter-wave band,such as,coaxial magnetron,inverted coaxial magnetron,low magnetic field conventional magnetron and spatial harmonic magnetron(SHM).SHMs can be considered as the most successful alternative to conventional magnetrons.Compared to the conventional magnetron utilizing principal harmonic of ? mode,the main advantages of the SHM come from the following: First,the application of the ?/2 mode or its adjacent mode with a backward working harmonic helps decrease the DC magnetic field and increase the magnetron cavity dimensions by about two times.Second,this operating mode has much better mode separation in both frequency and phase velocity domains.Until now,the SHM is still in infancy in domestic research.Based on this,the SHM's mechanism and operating characteristics of W-band of non-? mode spatial harmonics of the magnetron have be analyzed and researched,this will be fill with the vacancy.Firstly,multimode transient property,non-? mode and space harmonic theory in unstrapped resonator are systematically analyzed.The limitation of convention magnetron not operating at the high frequency and the advantages of W-band magnetron operating with non-? mode and synchronizing with backward harmonic are found.The transient behaviors of multimode self-excitation in the unstrapped resonant system are discussed and the influence of mode selection on cavity dimension,mode separation and Q factor is described.Then,the operation curve and load curve of the magnetron synchronizing with space harmonic are deduced.Secondly,based on the references and theoretical analysis,the efficiency performance of W-band harmonic magnetron is discussed on the behavior of beam-wave interaction and loss at high frequency.The main reasons of high efficiency of the conventional magnetron and low efficiency resulted by the angular velocity,high-order space harmonic and RF loss in SHM are presented.Baseing on this theory,some methods of improving efficiency are suggested.Thirdly,on account of theoretical analysis,the simulation model of W-band SHM is built and many simulation results about the characteristics in cold test and hot test condition are given.The simulation analysis could give the direction of improving experimental process and it is the significant foundation of experiment.Then,with the theoretical calculation of simulation analysis,a W-band SHM which operates with adjacent mode of ?/2 mode is firstly fabricated successfully at domestic.The electron in the interaction space synchronizes with the first backward space harmonic and the power of this SHM is more than 2kW.Therefore,the theoretical calculation and simulation analysis are proved correctly.Finally,basing on the experimental of W-band SHM,the cold cathode technology is developed.The theory of cold cathode magnetron is analyzed.According to the experimental result,the feasibility of millimeter magnetron with auto-emission cold cathode and cold cathode with auxiliary thermionic cathode is proved. |
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