Research On Key Technologies Of Compact High Efficiency Millimeter Wave Extended Interaction Devices

Millimeter wave is electromagnetic wave in the range of 30GHz to 300GHz.Vacuum electronic devices have important application value in the field of civil and national defense in millimeter wave band,especially the millimeter wave vacuum electronic devices with high working frequency,high efficiency,high power,high reliability,low voltage and miniaturization have become the research hotspot of this kind of devices in recent years.The extended interaction device combines the characteristics of klystron and traveling wave tube technology.It has the advantages of small size,light weight,low working voltage,wide bandwidth and high power.It is a compact vacuum electronic device and has great development potential in millimeter wave band.It has become the research focus of high frequency millimeter wave source.However,when the frequency of the extended interaction device increases in the millimeter band,the size of the device decreases?to the order of submillimeter?,which brings a series of technical problems,such as:the traditional circular electron beam channel is very small?far less than the millimeter wave length?,and the allowable current decreases;the size of the interaction gap is reduced,which is easy to cause RF breakdown;and the high frequency loss of the circuit.These problems lead to the decrease of electronic efficiency and power,even no power output.In order to solve the problem of device efficiency reduction caused by the increase of millimeter wave band frequency,this dissertation proposes to use higher-order mode working mechanism to make the single beam device have larger size than the basic mode mechanism at the same frequency,so that the device still has a certain power output after the frequency is increased;the idea of power synthesis is proposed to enhance the device power and verify its feasibility;for the basic mode and higher-order mode millimeter wave device,the device has a certain size The mechanism of beam wave interaction for improving efficiency is studied.The main work and innovation of this dissertation are as follows:1.In this dissertation,the fundamental theory,simulation and experiment of millimeter-wave extended interaction oscillator are studied,and the mode distribution optimization technology to avoid mode competition is proposed,and the working mechanism of fundamental mode is studied.The cold test and hot test are carried out for the basic mode device.The probe excitation method and waveguide feeding method are used to obtain the basic mode 2?mode frequency of 35.8GHz.The hot test results show that the device can work stably in 2?mode,and the test frequency is consistent with the cold test,which verifies the correctness of the design,and lays a foundation for the improvement of efficiency and power in the follow-up.2.In order to solve the problem of power reduction caused by frequency increase,a power combining method is proposed to form an extended interaction power combining circuit by cascading multiple small size devices in an angular direction,and an output circuit which is conducive to power synthesis is proposed.This synthesis method has the following three characteristics:?1?after cascading,several single cavity circuits are distributed on the same circumference to form a distributed hollow electron beam,which can share the same magnetic focusing system;?2?the introduction of multiple electron beams improves the total conductivity of the electron gun;?3?it can increase the transverse circumference diameter to form a larger scale power synthesis in the angular direction To further improve the power.The distributed hollow beam interacts with the field uniformly distributed in the new circuit,which makes the device generate10kW power and 103GHz frequency under the condition of 27kV beam voltage and4.2A current.This kind of circuit provides an effective method to improve the power of millimeter wave extended interaction device.3.Aiming at the problem that the device can not work normally due to the decrease of power capacity and the increase of high-frequency loss after the frequency increases,a high-order mode operation mechanism suitable for this kind of device is proposed,which aims to make the device still have a certain power output after the frequency is increased.Based on the analysis of fundamental mode operation mechanism,the transverse distribution transformation of fundamental mode and higher-order mode field is carried out,and a Ka band TM₃₁1 mode extended interaction oscillator is designed.The conversion study shows that the TM₃₁1 mode mechanism can support the extended interaction circuit with the transverse size twice the working wavelength at the same frequency as the fundamental mode,and increase the power capacity.The results of particle simulation show that the TM₃₁1 mode oscillator can generate 26.3kW power with an efficiency of 14.4%at 61kV and 3A current.When the frequency is further increased to W-band,a design method is proposed to make the extended interaction circuit work stably in TM₃₁1 mode mechanism by using the distribution characteristics of transverse standing wave half wavelength field,so as to avoid mode competition.Under the condition of 20.5kV electron beam voltage and 8A current,the designed W-band device achieves a power output of more than 10kW with an efficiency of 6.5%.4.When the frequency is further increased to the upper limit of 300GHz in millimeter band,the circular electron beam is not enough to support the current required for power enhancement due to the further reduction of device size.Therefore,a combination of high-order mode mechanism and sheet beam technology is proposed to improve the efficiency and power of the device at high frequency requirements.A300GHz high-order mode sheet beam extended interaction circuit is designed.A high-order mode design method matching with the critical cut-off operating conditions of the sheet beam device is proposed.The effectiveness of the design method is verified by analyzing the three-dimensional electromagnetic characteristics of the circuit.With the same level of processing technology and the same material,the surface current distribution of this high-order mode sheet beam circuit can effectively reduce the high-frequency loss under certain energy storage conditions,which is conducive to the improvement of device efficiency.5.Based on the space charge wave theory,the mechanism of beam wave interaction is studied to improve the efficiency.The equilibrium relationship between electron coherence and depolymerization effect is mainly studied between electron beam current density and filling factor.The results show that when the beam diameter of the fundamental mode oscillator decreases from?/8 to?/40??is the working wavelength?,the efficiency increases by 10.5%,and continues to decrease to?/80.When the filling factor of the high-order mode oscillator decreases from 100%to 0.36%,the efficiency increases by 6.8%.When the filling factor continues to decrease,the efficiency decreases.The results show that:at the same electron beam current,decreasing the beam filling ratio?i.e.increasing the current density?can enhance the electron coherence and improve the device efficiency when the electron beam is weak;if the electron beam filling ratio continues to be reduced,the depolarization effect will be enhanced,the coherence will be poor,and the efficiency will be reduced.In addition,the electron clustering characteristics after beam wave interaction are analyzed,and the phase velocity resynchronization technology is used to improve the electron clustering quality after energy delivery.According to the electron energy distribution after beam wave interaction and the multi cavity klystron management concept,the non-uniform periodic structure is designed,which increases the efficiency of the fundamental mode device by 2%.