Study On Sheet-beam Folded Waveguide Based On UV-LIGA Technology

With the development of terahertz technology,it has played an important role in electronic information,environmental monitoring as well as telecommunication and radar technology.The transmission of terahertz wave is an important part of high-frequency telecommunication system.It is very hard to guide and control the transmission of terahertz wave in a way.To overcome this difficulty,it is badly in need of the waveguide which can transmit terahertz wave.Folded waveguide slow wave structure is an important kind of THz passive waveguide device which is often used as the core part for beam-wave interaction in travelling wave tube.Folded waveguide is an all-metal periodic structure.In the plan of High Frequency Integrated Vacuum Electronic device(HiFIVE)by DARPA,it has reported a 220 GHz travelling wave tube with high power and big gain which is used for radar exploring and imaging since 2009.In nowadays,the plan is a cutting-edge representation of THz technology.This essay is based on folded waveguide.Starting with novelty and practicability,the essay focuses on series simulation and fabrication about folded waveguide.The essay content mainly includes:Starting from transmission line theory,the high frequency transmission characters of the folded waveguide including none-ridge and double-ridge were analyzed by using equivalent circuit theory and cascade matrix method.By using MATLAB,the dispersion and interaction impedance were calculated.By using 3D EM simulation software CST,the dispersion and interaction impedance were also simulated.In simulation process,parameter modeling and structure dimensional errors were adopted.Simulation results showed the dispersion of none-ridge folded waveguide was flat at 140 GHz and the phase velocity was near 0.22 c.The interaction impedance was about 5 ohm.The dispersion of double-ridge sheet-beam folded waveguide was close to none-ridge structure,but the interaction impedance was increased to 6.2 ohm.The error analysis of main structure parameters provided reference for practical fabrication.The beam-wave interaction in the folded waveguide was simulated by using Particle Studio in CST software.Simulation results showed the power gain of double-ridge sheet-beam folded waveguide at 140 GHz reached 24.6 dB and the gain per unit length reached 0.401 dB/mm.Simulation results also showed the output power gain had a big change under different emission voltage,input frequency and input power.The simulation results provided guidance for debugging and testing.The fabrication accuracy and integration of UV-LIGA were better than conventional machining method.In this essay,the none-ridge and double-ridge sheet-beam folded waveguide sample were fabricated by using SU-8 UV-LIGA process.The essay studied the feasibility of sheet-beam folded waveguide by using UV-LIGA process.This essay explored the basic UV-LIGA process for folded waveguide fabrication,including mask design,substrate,exposure and developing parameters,electroplating and removing photoresist and so on.Finally,the essay formed a performance evaluation scheme for the sample fabrication of folded waveguide by using UV-LIGA process.Finally,the transmission parameters of sheet-beam folded waveguide were tested.The test showed the return loss of none-ridge folded waveguide was about-27 dB and the insertion loss was near-3 dB;the insertion loss and return loss of double-ridge sheet-beam folded waveguide were-25 dB and-5 dB respectively.At last,the output power of none-ridge folded waveguide reached 28 W at 139.5 GHz.At the same time,the power and gain were 26 W and 21 dB at 140 GHz.The output power of double-ridge sheet-beam folded waveguide was from 29 to 32.5 W when the frequency was from 139 to 141.5 GHz.The max output power reached 32.5 W when the frequency was 140.5 GHz and the power gain was close to 23 dB.The results showed UV-LIGA process achieved the high fabrication accuracy of folded waveguide.