Design And Fabrication Of Terahertz High Power Slow Wave Structure

With the increasing rate of data transmission,the traditional microwave signal has been unable to meet the requirements of high-speed transmission of mass data.Terahertz wave has become a hotspot of wireless communication research in the world because of its long bandwidth,accurate direction and high security.Although terahertz technology has unique advantages and broad application prospects,it is difficult to control its generation and dissemination in some ways.High power vacuum micro-electronic device is one of the effective technologies to realize terahertz radiation source.In particular,the traveling wave tube(TWT)based on folded waveguide slow wave structure is the most promising vacuum micro-electronic device at present.As the core component of TWT,folded waveguide slow wave structure has many advantages,such as high power,wide bandwidth and firm structure,which is the focus of many scholars.Taking the TWT slow wave structure as the research object,aiming at practicability and innovation,the traditional folded waveguide and folded waveguide loaded by new structure are studied theoretically and processed practically.The main tasks are as follows:Based on the transmission line principle,the discontinuous interface of folded waveguide is analyzed by equivalent circuit method.The high frequency characteristics of folded waveguides are studied and their expressions are derived.The dispersion characteristics and coupling impedance of 220 GHz folded waveguides are calculated by using MATLAB software.HFSS software is used to simulate the electromagnetic field.The simulation results have the same trend as the calculated values,with a deviation of less than 2%.This verifies the correctness of the equivalent circuit method and lays a foundation for the design of a new slow wave structure.The characteristics of various new slow wave structures and the feasibility of fabrication are analyzed.H-plane ridge-loaded folded waveguide can not only effectively improve the power gain of terahertz TWT,but also be compatible with UV-LIGA.It is the most promising terahertz slow wave structure.A H-plane ridge-loaded folded waveguide at 340 GHz is designed.The designed structure has good dispersion characteristics near the central frequency,and the interaction impedance value is increased from 5.5? to 9?.The beam-wave interaction simulation with CST software shows that the power gain of folded waveguide TWT is 30.5dB,the gain per unit length is about 1.173dB/mm,the bandwidth of 3dB is from 335 GHz to 345 GHz,the saturated output power is over 50 W,and the maximum electronic efficiency is about 6.0%.These performances have certain advantages and novelty.UV-LIGA technology combined with SU-8 photoresist can not only realize the processing of high aspect ratio structure,but also ensure high surface quality,so this method is used to process H-plane ridge-loaded folded waveguide.The key points and difficulties in the process of UVLIGA are analyzed and discussed,and a complete processing scheme of slow-wave structure is explored.The possibility of using UV-LIGA technology to process other new slow wave structures is attempted.The S-parameters of 340 GHz H-plane ridge-loaded folded waveguide are tested on the test platform.The center frequency of ridge-loaded folded waveguide is around 342 GHz,the echo loss of waveguide is less than-10 dB,the minimum is-37 dB,and the absolute insertion loss is less than 2 dB,the minimum is 0.5 dB.From the test results,it can be seen that the processed slow wave structure has good transmission performance,which proves the correctness of the design and the accuracy of UV-LIGA process.