Slow-Wave Characteristics of a Frame–Rod Structure Based on Micro-Fabricated Technology for THz Vacuum Electron Devices

A simple equivalent circuit analysis of the frame–rod slow-wave structure (SWS) on dielectric substrates of a traveling-wave tube (TWT) is developed, using the quasi-TEM approximation approach for the dispersion and coupling impedance characteristics of the structure. Moreover, the obtained complex dispersion equation and coupling impedance are numerically calculated. The calculation results by our theory method agree well with the results obtained by the 3D EM simulation software HFSS. It is shown that the dispersion of the frame–rod circuit is decreased; the phase velocity is reduced and the bandwidth becomes greater, while the coupling impedance decreases after filling the dielectric materials in the frame–rod SWS. In addition, a comparison of slow-wave characteristics of this structure with a rectangular helix counterpart is made. As a planar slow-wave structure, this structure has potential applications in compact TWTs based on the micro-fabrication technology, which could be scaled to millimeter wave, even to THz frequency.     

Investigation of Double-groove Loaded Folded-Waveguide Slow-wave Structure for Millimeter Traveling-wave Tubes

To enhance the strength of beam-wave interaction and improve the performance of gain, the double-groove loaded folded-waveguide slow-wave structure (SWS) is proposed for millimeter traveling-wave tubes (TWTs). In the first part, the expressions for the dispersion and the interaction impedance of this novel structure are obtained by using matching conditions of the RF fields. Ansoft HFSS is also used to calculate the high frequency characteristics. The simulation results from HFSS agree with the theoretical results. Numerical calculation for different combinations of the groove width and depth is carried out to study the influence of groove loading on the properties of this novel circuit. In the second part, a linear theory of a double-groove loaded folded-waveguide TWT is developed and calculated for analyzing the effect of groove dimensions on the property of small signal gain. The investigation results indicate that the interaction impedance is obviously raised up and the small signal gain are enhanced by loading groove in the FWSWS.     

Design of Tip Loss Profile on Support Rod for a Helix TWT

This paper describes the design of tip loss profile on support rod for a high gain, high efficiency helix TWT. The tip loss profile at sever ends for the input and the output section of the helix slow wave structure has been designed for return loss at severs ends better than -20 dB. The experimental results have been carried out in the input and the output section of the helix assemblies for the high gain helix TWT to find the return loss in the region of carbon coated tip loss on the support rods. The experimental result has been compared with the simulated performance for the return loss at the sever ends. The design of tip loss profile on the support rod for helix TWT has been carried out in real situation using Ansoft HFSS. A good agreement has been found in the simulated and experimental results.     

Design of Coaxial Couplers for High Efficiency Helix TWT

The main objective of the paper is to make an efficient design of the input and output coaxial coupler for a helix TWTs. An approach has been developed for the efficient design and analysis of the coaxial couplers in the practical situation. Normally multi-section impedance transformer approach is used for any wide band coupler. For a space helix TWT, coupler should be wide bandwidth and small size. In this case coupler is matched with helix slow wave structure and the standard 50-ohm connectors. The simulated return loss (dB) profile for different type of couplers is obtained by using Ansoft HFSS, CST microwave studio and compares those with experimental results. The tip loss design at sever ends for the input and the output section has been also optimized.     

一种具有新型分立介质支撑的翼片加载螺旋带慢 波结构的研究

本文研究了一种具有新型分立介质支撑的翼片加载螺旋带慢波系统,该种慢波系统具有较高的功率容量和较宽的带宽.通过用切比雪夫多项式来展开螺旋带上的面电流,用真空层来模拟螺旋带的厚度,用均匀分层介质来等效新型分立介质支撑,考虑到过渡连接金属块的影响,用场论的方法得到了非常实用的色散方程和耦合阻抗的表达式,同时进行了HFSS模拟,发现用场论的方法所得出的结果与用HFSS模拟的结果吻合良好.本文的结果对这种新型慢波结构的设计具有指导意义.     

Analysis of the Dispersion Characteristic and Interaction Impedance of a Tape Helix Slow Wave Structure with Novel Supporting Mode

In order to enhance the power capability of the helix travelling wave tube, a novel tape helix slow wave structure (SWS), which is supported by helically arrayed radial dielectric-support posts, is developed. Each dielectric post can be easily brazed with the tape helix and the metal envelope by means of a special soldering. This kind of supporting mode can protect the dielectric supporting posts from being broken by the thermal stress in the case of high temperature. A hybrid model is set up in consideration of the influences of both the radial thickness of the tape helix and these discrete dielectric-support posts. The dispersion equation and interaction impedance of the helical SWS are obtained. The calculated results using this hybrid model presented in the paper show good agreements with the HFSS simulation results. All the results presented here can provide a good basis for designing the novel tape helix SWS.     

大直径波纹内导体同轴慢波结构特性的研究

提出了易以加工的大直径波纹内导体相对论返波振荡器慢波结构,推导了这种慢波结构的冷色散方程和耦合阻抗计算公式,数值计算并详细分析了相关结构参数对TM_0n模式色散曲线分离度以及TM₀₂模式的高频场耦合阻抗的影响.结果表明:慢波结构周期、波纹深度以及电子注平均半径都对高频场耦合阻抗有影响;这种慢波结构在抑制模式竞争、以及在低引导磁场下工作等方面都有较大的优势.     

Wave Properties of A Free Elliptical Helix Slow-Wave Structure with Arbitrary Eccentricity

This paper gives the investigations of the fundamental wave of a free elliptical helix slow-wave structure (SWS) with arbitrary eccentricity. The wave properties including the phase velocity characteristics, interaction impedance and the longitudinal electric field distribution of this mode has been fully studied. It is found that, when the eccentricity increases, the interaction impedance and the operating frequency of such SWS will be improved, which allows to have a higher gain and operating in a higher frequency band. Furthermore, the field configuration is different from that of a round helix; the azimuthal distribution of the E-field follows with the angular Mathieu function of the first kind, even with mode of zero. In radial, E-field is elliptical surface wave. When the eccentricity tends to zero, all the characteristics will be smoothly degenerates to the case of round helix correspondingly.     

矩形波导加载光栅结构的太赫兹振荡器

本文采用矩形波导加载光栅的慢波结构作为太赫兹返波管的高频结构,通过理论分析和电磁仿真研究了该慢波结构的色散特性和互作用阻抗,理论分析结果和仿真结果能很好地吻合。在理论分析的基础上,设计了一个中心频率为340GHz的返波管,经粒子模拟软件计算,在较低电流密度的情况下该返波管输出功率达100mW且可调带宽约30GHz。     

螺旋线慢波结构冷特性自动测量系统

介绍了一种用于螺旋线慢波结构模型色散特性和耦合阻抗的自动测量系统,它以非谐振微扰法为理论基础,硬件系统包括矢量网络分析仪、PC机、电移台、机械结构、光学监测装置等,并研制了专用的测量控制和数据处理软件。该系统实现了螺旋线慢波结构测量的自动化控制,人机界面友好,测量进程控制灵活,可以直接给出2～20 GHz频率范围内的色散特性和耦合阻抗的频响曲线。测量对象为行波管研制中所用螺旋线慢波结构的1∶1模型。