Simulation Research On Ka-band Nano-Cold Cathode Coupled Cavity Traveling Wave Tube

As a broadband millimeter wave and terahertz radiation source amplifier,traveling wave tubes have been extensively studied.In the study of traveling wave tubes,both the cathode and the slow wave structure play an important role.Field emission cold cathode has many superiority over hot cathode.For example,it starts fast,can operate at room temperature,has a small size and low cost.Aiming at the development needs of the miniaturization of millimeter wave devices,a new type of nano-cold cathode coupled cavity traveling wave tube is theoretically researched in the paper.The main work includes:1.A new type of cold cathode electron gun is simulated and researched.Combining the working characteristics of the nano-cold cathode electron gun,a new type of cold cathode electron gun structure is emphatically studied in the paper.Through the relationship between the different structural dimensions of the electron gun and the emission performance to obtain their degree of influence.The crucial size of the electron gun is continuously improved.Finally,the electron gun structure and electron beam trajectory that meet the needs are acquired.The optimization results show that the ring electron beam is acquired,the outer radius is 1.2mm,the inner radius is 1.0mm and the emission current can reach 146 m A.2.The high-frequency interaction system with a porous coupled cavity slow-wave structure is designed and researched.The main work includes the design of slow wave structure and the input and output structure.In the first step,by studying the performance of the slow-wave structure with different coupling hole distributions,the structure is determined.The slow wave structure is a symmetrical structure with uniformly distributed three-coupled holes.The electron beam channel has a large radius.Based on research of high frequency characteristics,the effect of different structure sizes is analyzed and optimized in CST.The control variable method is used to scan the key structure size to get the best size.In the second step,based on the design of the porous coupling cavity type slow wave structure,the input and output structure adopts a stepped transition waveguide structure.They can achieve a better match.In the operating frequency range of 33-34.4GHz,the S11 parameters of the high-frequency system are basically below-20 d B.Around the operating frequency,the value of the S11 parameter is less than-25 d B.3.The wave beam interaction of cold cathode traveling wave tube is studied.Combining the cold cathode electron gun,high frequency system and collector to establish the entire tube model.The thermal cavity simulation of the traveling wave tube is launched.The simulation results show that when the emission voltage is 28 k V and the emission current is 146 m A,the output power can reach 153 W at 33.4GHz,the gain can reach 25 d B,and the 3d B bandwidth is about 0.6GHz.The design of cold cathode traveling wave tube can meet the requirements.