Power Combining And Array Design Of Millimeter Wave Magnetrons

For directed energy weapons and other domains,the output power of a single millimeter wave source always has a limit and therefore cannot satisfy the demand for higher power in these domains.Therefore,the task of finding a millimeter wave source with sufficient output power and high efficiency becomes more urgent.One technical solution is to couple millimeter-wave sources together to form a power-combining magnetron array.Among the many millimeter-wave sources,a millimeter-wave magnetron is a vacuum electronic device with high efficiency,small size,light weight,compact structure,etc.Therefore,multiple millimeter wave magnetrons coupled together through a coupling bridge to form a power combining array is an effective technical solution to break the output power limit of a single millimeter wave source.Although this technical solution faces problems such as increasing system complexity,such an array has important research value and broad application prospects given the high efficiency and compactness of the millimeter-wave magnetron itself and the advantages of the equivalent omnidirectional radiated power of the coherent signal output,which increases with the number of magnetrons n~2.This dissertation addresses the power combining of millimeter-wave magnetrons and their array design,this dissertation analyzes and explores the preliminary theory and various key technologies for the power combining and array design of millimeter-wave magnetrons.Firstly,for the first time,the high-efficiency phase-locking mechanism was revealed by theoretical studies.Utilizing simulation methods,the feasibility of this mechanism was verified:(1)The reasons for two types of energy losses during the phase-locking process,namely impedance mismatch losses and frequency mismatch losses,were analyzed and investigated.The property that no energy is lost during phase locking under the ideal conditions of perfectly matched impedance and perfectly matched frequency was found and analyzed,thus revealing the high-efficiency phase-locking mechanism;(2)A circuit model for phase-locking magnetrons with zero energy loss was established using an approximate equivalent circuit approach.A frequency equation of the two modes of high-efficiency mutual coupling phase-locking circuit was derived,and the competition mechanism between these two modes was analyzed based on the frequency equation,which pointed out the direction of the optimization of the coupling bridges;(3)Eigenmode,time-domain,and PIC simulations were performed on a phase-locking circuit composed of two rising-sun magnetrons.Firstly,the competition mechanism between the0 phase-difference mode and theπphase-difference mode was verified by the eigenmode and time domain simulations.Secondly,the optimization of the coupled bridge structure was completed.The optimized coupling bridge structure increased the frequency difference between the 0 phase-difference mode and theπphase-difference mode,and the competition between the two modes was weakened.Finally,the circuit was verified to operate in the highly efficient phase-locking regime by the PIC simulations:the phase-locking efficiencies of the circuit reached up to 99.9%for both the 0 phase-difference mode and theπphase-difference mode.Furthermore,this dissertation investigated the impact of the magnitude of frequency mismatch on the phase-locking efficiency under the premise of the optimized coupling bridge structure was investigated.The revelation of the high-efficiency phase-locking mechanism laid a theoretical foundation for the subsequent power combining experiments as well as the multi-magnetron arraying technology.Subsequently,building upon the research foundation of high-efficiency phase-locking mechanism,the design of a modular millimeter-wave coaxial magnetron and the simulation and experimental verification of high-efficiency phase-locked dual-magnetron were completed.Preliminary validation of the high-efficiency phase-locking mechanism was conducted in the millimeter-wave frequency range for the first time:(1)A modular coaxial magnetron was designed then simulations were performed in both eigenmode and PIC simulations of free-running magnetrons(coupling port connected to the shorting plate)and phase-locked magnetrons.The simulations yielded phase-locking efficiencies of up to 98.9%for the 0 phase-difference mode and 99.5%for theπphase-difference mode,respectively.These simulations proved that the circuit operated in the high-efficiency phase-locking regime;(2)Cold tests were performed on the modular coaxial magnetron,including calibration of the cold test system,cold tests on the single-module coaxial magnetron,cold tests on the phase-locking magnetrons,and calibration of the power combining system;(3)Finally,experiments of modular coaxial magnetrons A and B in free-running oscillation,along with the analysis and comparison of their results were performed.In addition,the experiments of power combining after phase locking of coaxial magnetron A and B were conducted:phase-locking efficiency was approximately93.4%for the 0 phase-difference mode,and 95.6%for theπphase-difference mode.The results reached the international advanced level in the millimeter-wave band.With the continuous optimization and improvement of the design and experiment,it is very promising that the measured phase-locking efficiency will become close to the simulation results.Finally,preliminary research on arraying technology was conducted,expanding the application scope of the high-efficiency phase-locking mechanism:(1)PIC simulations were performed on high-efficiency phase-locking magnetrons with unsynchronized high-voltage pulses,proving the effectiveness of the high-efficiency phase-locking mechanism when unsynchronized high-voltage pulses were applied:The simulation and analysis of a phase-locked circuit composed of two rising-sun magnetrons operating under two unsynchronized high-voltage pulses were conducted.The results revealed that the envelope of the output signals from magnetrons A and B exhibited a two-level staircase shape.The phase-locking of the two magnetrons occurred within the second stage of the staircase;(2)The preliminary study of this mechanism in multi-magnetron scenarios demonstrated the potential of applying the high-efficiency phase-locking mechanism to small-sized and medium-sized arrays:Analyses of a(1×3)magnetron array with different combinations of coupling bridge lengths.PIC simulations were performed for these different combinations of coupling bridge lengths.The PIC simulation results indicated that all of them operated in the high-efficiency phase-locking regime.In addition,designs and analyses were performed for(2×2),(2×3),(2×4),and(3×3-1)magnetron arrays with all coupling bridge lengths equal to one guide wavelength.The PIC simulation results showed that the operating modes of adjacent magnetrons in these arrays were all the 0-phase difference mode and the above four types of magnetron arrays operated in the high-efficiency phase-locking regime.This work extended the applicability of the high-efficiency phase-locking mechanism of two magnetrons to magnetron arrays with three tubes and up to eight tubes.