Research On Electronic Optics System And Backward Wave Oscillator Based On Carbon Nanotube Cold Cathode

The high-power terahertz wave system is composed of a power source,a transmission system,and a transmission system,and has a wide range of applications in the fields of communication,radar,imaging,and medicine.Transmission systems include input-output coupling systems,mode converters and low-loss transmission systems,etc.,which are the key to the effective application of high-power terahertz waves.The main content of this paper is to design a waveguide transmission system,the output mode is TE₀₃ mode,the terahertz signal output by the cyclotron oscillator with the working frequency of 220 GHz is transmitted to the input port of the cyclotron amplifier.The mainly proposes solutions to key issues such as transmission efficiency,conversion efficiency,bandwidth,and ease of fabrication in transmission devices in high-power,terahertz wave-band circular waveguide mode converters,circular waveguide bends,and input systems.And verified by theoretical calculations and experiments.The research content of this dissertation is as follows:1.A cascaded TE_0n mode converter with linearly tapered radius for 220 GHz gyrotron is proposed.It can effectively reduce the difficulty of implementing the high-frequency mode converter.A numerical calculation program based on coupled wave theory was written,and TE₀₂-TE₀₁mode converters of different lengths were optimized.A mode converter with a length of 136 mm(8 segments)and a conversion efficiency of95%-98.78%in the frequency band between 215 GHz and 225 GHz is obtained.Under the same design scheme,a length of 92 mm(8 segments)TE₀₃-TE₀₂ mode converter with a conversion efficiency higher than 95%and in the working frequency band is obtained.And it has a conversion efficiency of 98.44%at the operating frequency of220 GHz.The simulation results of the above-mentioned mode converters are in good agreement with the theoretical calculation results,with only varying degrees of frequency deviation.A near-field scanning system was built using the loss network analyzer.By scanning the field components of the input and output ports of the tested device,the purity and transmission loss of the input and output modes of the device can be obtained.This paper selects TE₀₃-TE₀₁ composed of 65.43 mm(4 segments)TE₀₂-TE₀₁ mode converter and 92 mm(8 segments)TE₀₃-TE₀₂ mode converter TE₀₃-TE₀₁ for experimental verification.In the frequency band 215-225 GHz,the output TE₀₃ mode The purity of the model is 82%,and has low transmission loss.2.A cascaded TE₀₁-TE₁₁ mode converter with a fold line circular-waveguide is proposed,and the coupled wave equation and coupling wave coefficients in the tortuous waveguide are derived from the coupled wave theory.Through the optimization of the calculation program,the conversion efficiency of TE₀₁-TE₁₁ tortuous circular waveguide mode converter reaches 96.8%.In the simulation verification,the maximum conversion efficiency of the mode converter is 98.8%(218.3 GHz),and the conversion efficiency within 215.3?221.6 GHz is greater than 90%.The mode converter has been processed and tested.The test results show that the input mode purity of TE₁₁ mode is 90%in the211.5-214 GHz band,the mode purity of the output port TE₀₁ mode is close to 90%,the mode conversion efficiency reaches 95%,and the average transmission loss is-1 d B.3.In this chapter,the right-angle steering transmission of TE₀₁ mode in circular waveguide is studied.Successfully designed the grooved TE₀₁ mode waveguide elbow and TE₀₁ mode square waveguide elbow through simulation.The simulation results show that the transmission of the grooved waveguide elbow in the 216-224 GHz frequency band is close to-0.5 d B,and the reflection is less than-15 d B;the square waveguide elbow in the 210-230 GHz frequency band,its transmission loss is less than-0.1 d B,and the reflection is less than-30 d B.The square elbow has been experimentally verified,and the result is that the average purity of the TE₀₁ mode of the output port in the 216-228 GHz frequency band is 80%.This paper also conducts theoretical and experimental research on the over-mode beveled elbow.The mode purity of the TE₀₁ mode output in the 210-230 GHz frequency band of the beveled elbow with a radius of 5 mm is 85%-90%,and the average value of the transmission loss is-1 d B.The purity of the TE₀₁ mode output by the bevel elbow with a radius of 10 mm in the frequency band of 216-230 GHz is 60%-80%,and the average value of the transmission loss is-1.5 d B.4.A pill-box window for 220 GHz amplifier was studied,and the design,production and testing of the window were completed.The design,production and testing of the window have been completed.The experimental results show that in the215-225 GHz frequency band,the box-shaped window has a transmission loss of about-0.5 d B and a reflection of-11 d B.