Research On The Theory And Key Technologies Of Extended Interaction Devices

As a miniaturised vacuum electronic device with the advantages of wide tuning,high power and small size,the extended interaction device is an important microwave source,which is widely used in military and civil fields.With the vigorous development of modern high-frequency technology,new requirements have been put forward for extended interaction devices,prompting their rapid development towards higher frequency,higher power and wider tuning.The high frequency extended interaction device has a small cavity size and limited power capacity,and its tuning bandwidth is limited due to its own working mechanism.When the operating frequency rises to a higher frequency band,the traditional extended interaction device will also have problems such as reduced power capacity and increased processing difficulty,so that the output power of the device will be reduced.In order to solve the series of technical problems in the development of extended interaction devices and explore the huge development potential of extended interaction devices in high frequency band,this dissertation focuses on the theme of extended interaction devices,and starts with technical difficulties such as high frequency,wide tuning and high power,and carries out theoretical analysis,circuit design and experimental measurement.The dissertation provides solutions to the key technical problems in the development of extended interaction devices.The main work and innovations of the dissertation are as follows:1.In this dissertation,the circuit of extended interaction device is firstly analysed and studied in basic theory,and a millimetre-wave high-power extended interaction oscillator operating at 95 GHz in the fundamental mode is developed based on the theoretical study for the miniaturised and high-power application requirements of the extended interaction device.The extended interaction oscillator adopts a band electron injection with a large aspect ratio to enhance the energy density input,and a multi-gap periodic structure as the interaction substrate to increase the power capacity.Focusing on solving the technical problems related to the stable transmission of the ribbon injection,the high-frequency structure was cold tested and the entire extended interaction oscillator was thermally tested,finally obtaining a high-power signal output of 2.1 k W at 20%duty cycle.The experiment verifies the feasibility of the designed circuit,and the device can work stably in single mode and output a signal power of 95GHz stably.This experiment is of great significance in guiding the generation of high power signal source by high frequency band extended interaction devices.2.A multimode electrically tuned broadband circuit structure is proposed to address the problem of the conventional millimetre-wave extended interaction device with its electronically tuned range limited when it operates in single mode(TM₁₁-2πmode).Based on the analysis of the cavity equivalent circuit theory and waveguide discontinuity theory,the relative sizes of the coupling cavity width and the coupling gap width,as well as the effects of different positions of the coupling holes on the extended interaction cavity characteristics are investigated,i.e.,when the width of the coupling cavity is smaller than the width of the coupling gap,multiple successive peaks will be stirred up on the S11 pattern of the extended interaction circuit,whereas the modes can be further reduced by offsetting the coupling holes gap,and ultimately the tuning between multiple modes and continuous output can be achieved.Based on this relational property,a coupled-aperture-biased multimode electrically tuned broadband circuit structure is designed to achieve continuously tuned output over 1 GHz in the electrically tuned band.The continuous tuning operation between the standing wave mode and other modes with large characteristic impedance near this mode can increase the frequency tuning range of the extended interaction device,which is of great significance in expanding the applications of the extended interaction device.3.In order to achieve ultra-wideband tuning of extended interaction devices,a novel mechanically tuned multimode hopping extended interaction circuit is proposed based on the study of the strong and weak coupling characteristics of the extended interaction cavity.By analysing the phenomenon of large jumps in the resonant frequency of the cavity caused by small changes in the width of the coupling cavity under the weak coupling characteristics,it is proposed to mechanically tune the width of the coupling cavity under the weak coupling characteristics in order to achieve the ultra-wideband tuning of the extended interaction circuits.By analysing the mode hopping and mode coupling matching during the mechanical tuning process,it is established that the circuit structure achieves ultra-wideband tuning of nearly 10 GHz under the mechanical tuning of the coupling cavity width of 0.8 mm.The novel tuning method is an effective combination of mechanical and electronic tuning,and provides a new approach to expanding the tuning bandwidth of extended interaction devices.4.In response to the problem of reduced power capacity brought about by the weakly coupled characteristic structure of electrically and mechanically tuned broadband tuned circuits,a new type of dual-coupling hole extended interaction circuit structure（X-EIO）is proposed.Two extended interaction circuit structures are cross-cascaded and share the same coupling gap cavity,thus forming a new circuit structure with four coupling cavities centre-symmetric.The electric field of this circuit structure is uniformly distributed at the centre.The four-side coupling cavity structure increases the energy coupling capacity in the cavity,and can be connected to the output structure in the adjacent coupling cavity to achieve dual-hole coupling dual signal output at the same frequency.The new dual coupling hole extended interaction circuit not only retains a certain tuning bandwidth,but also solves the problem of reduced energy output due to the narrowing of the coupling cavity width in the process of multimode electrical and mechanical tuning,and makes up for the shortcomings brought about by the weak coupling characteristics of the structure.5.Based on the problem that the output power of the extended interaction device in fundamental mode operation is limited by the size effect when the operating frequency rises to the terahertz band,a multi-gap wide-tuned terahertz extended interaction circuit based on TM₃₁mode operation and a low-injection terahertz extended interaction circuit based on TM₅₁mode operation are proposed.By comparing the characteristics of the cavity base mode and the higher-order mode and calculating the cut-off frequency of the cavity,the higher-order mode circuit structure suitable for multi-gap broadband tuning and the UHF extended interaction circuit structure suitable for single-mode operation in TM₅₁mode are designed,respectively.The broadband circuit based on the TM₃₁mode optimises the bandwidth limitation of the single-mode operation of the traditional high-power EID,and improves the output efficiency on the basis of certain broadband tuning.The circuit structure based on TM₅₁mode operation supports only TM₅₁-2πmode operation in the operating range,which can effectively inhibit mode competition,and the use of higher-order modes increases the cavity size and reduces the processing difficulty under the same frequency requirement,thus permitting terahertz energy signal output at low voltage-current injection.