The Mechanism And Realization Of A Coaxial Relativistic Backward-wave Oscillator With Frequency-tuning Across Both X-and Ku-bands

The relativistic backward-wave oscillator(RBWO)is one of the most promising high-power microwave(HPM)sources and has wide potential for industrial and military applications due to its essential characters such as high power,high efficiency and high repetitive rate.Frequency-tunable is one of the most directions of RBWO.However,the frequency-tunning method can't be easily performed and its frequency-tunning range is limited to a narrow band.In view of these limitations,a coaxial RBWO with frequency-tuning across both X-and Ku-bands is proposed.The central features contains,the operation frequency of the RBWO can jump across different bands;the operation frequency is tunable within each band;the tunning method can be easily achieved by merely altering the length of the inner conductor.The main content and innovative work are listed as follows.Firstly,the mechanism of the coaxial slow-wave structures(SWSs)with freque ncy-tuning across bands is investigated systematically.The dispersion curves of both the coaxial and hollow SWSs are obtained by numerical calculation and electroma gnetic-code simulation.The mechanism of the coaxial SWSs with frequency-tuning across bands can be achieved through mode selections and parameter optimizations of electron beam and SWSs.The cold cavities with frequency-tuning across C-,Xand Ku-bands are designed,which validates the mechanism of the SWSs with freq uency-tuning across bands.Considering practical application,the cold cavity with fr equency-tuning across X-and Ku-bands is analyzed intensively.The operation mode s of coaxial TM01 mode and hollow TM01 mode are chosen through the transversal mode selection.Moreover,the coaxial SWSs with a well-designed coaxial extractor can realize the longitudinal mode selection and enhance the beam-wave efficiency.Secondly,the mechanism of HPM generation from the device is investigated thoroughly by the 2.5-dimensional full electromagnetic particle-in-cell(PIC)code,and related physical images are presented.The dependences of the output microwave frequency,power and efficiency on structural parameters,beam parameters and guiding-magnetic field are analyzed in detail.It is shown that the frequency is lowered from10.64 GHz to 10.55 GHz when the inner-conductor length increases from 0 to 8.4cm.And the frequency is lowered from12.62 GHz to 12.51 GHz when the inner-conductor length increases from 8.5cm to 11.7cm,the frequency tuning bandwidth of both the X-and Ku-bands is about 1% at 3dB level.By merely altering the inner-conductor length under the condition of diode voltage at 680 kV,beam current at 12.8k A and guiding-magnetic field at 4T,the typical results are listed: a microwave with frequency of 12.58 GHz,power of 2.25 GW and efficiency of 25.9% is obtained in the coaxial structure;a microwave with frequency of 10.61 GHz,power of 2.20 GW and efficiency of 25.3% is obtained in the hollow structure.To enhance the beam-wave interaction efficiency,the other parameters besides the inner-conductor length are optimized.The optimization results are as follows: a microwave with frequency of 12.086 GHz,power of 2.67 GW and efficiency of 41.5% is obtained in the coaxial structure;a microwave with frequency of 9.92 GHz,power of 3.02 GW and efficiency of 34.5% is obtained in the hollow structure.In addition,the feasibility of the device operating under the low magnetic field is explored.Finally,the radiating system across both X-and Ku-bands is designed using high-frequency-field numerical software.The power transmission coefficients of 10.61 GHz and 12.58 GHz are both higher than 0.810,when 24 studdles are divided equally in two ranks.In addition,the mode converter and the hoghorn antenna are optimized,which achieves the mode conversion from TEM mode to TM01 mode.The efficiency of the radiation is 99.2%(10.61GHz)and 99.9%(12.58GHz),respectively.