CST MWS软件模拟三维螺旋线慢波结构

本文介绍了用CST MWS软件的周期边界条件计算行波管螺旋线慢波结构的色散和耦合阻抗等冷测特性的方法,用采取螺旋带模型的理论分析计算结果和实验测试值加以验证,取得了比较一致的结果;并应用这种MWS的模拟方法和螺旋带模型的计算方法分析了具有扇形和T形夹持杆慢波结构的冷测特性,结果表明,相速和耦合阻抗都随着扇形角度的增大而减小,随着T形窄端宽度的增加而减小,随着T形窄端高度的增加而增大.     

Tape Analysis of an Inhomogeneously-Loaded Helical Slow-Wave Structure for Broad-Band Traveling-Wave Tubes

Theoretical simulation of the dispersion and interaction impedance characteristics of an inhomogeneously-loaded helical slow-wave structure is validated. The structure is supported by double-curve-shaped rods which are smoothed out into a number of dielectric tubes with their respective effective permittivity values. The effects of the helix thickness are taken into account by considering a free-space gap equal to the difference between the mean helix radius and the outer helix radius. Moreover, the helix tape model is used instead of the simpler sheath-helix model. The theoretical predictions are compared with those of MAFIA simulation. The dispersion error is found to be within 3–6 percent and the impedance characteristic is in great agreement with that of MAFIA simulation. At last, for the sake of comparison, the cold-test characteristics under sheath-helix model are also provided.     

一种有限厚度翼片加载螺旋线色散特性及耦合阻抗研究

翼片加载螺旋线慢波结构广泛应用于大功率、宽频带行波管中.一般的计算未考虑翼片加载所引起的角向空间谐波,本文考虑空间谐波,建立了有限厚度翼片加载螺旋线慢波结构的模型,推导出实用的色散方程和耦合阻抗表达式.利用导出的方程对实际行波管的螺旋慢波结构进行计算,并与测量结果和简单翼片模型进行了比较.首次通过分析的方法得到加载翼片有最佳中心夹角(θ)存在.     

Analysis of a Chiral Dielectric Supported Broadband Helix Slow-Wave Structure for Millimeter-Wave TWTs

A novel technique of broadbanding a helical slow-wave structure through negative dispersion shaping is proposed. The model considers a simple continuous chiral dielectric support for the helix inside a metallic barrel, unlike conventional helix slow-wave structures with three discrete dielectric supports at 120⁰ apart. The dispersion relation of the slow-wave structure was derived following sheath-helix abstraction, suitably benchmarked for special cases, and was used for analyzing the dispersion behavior of a typical slow-wave structure. Chiral dielectric loading could easily provide negative dispersion characteristics (required for broadband operation) by merely controlling the chirality parameter alone. The scheme with its simple geometric configuration is expected to be useful for millimeter-wave devices providing better thermal management.     

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。     

Analysis of an azimuthally periodic vane-loaded cylindrical waveguide for a gyro-travelling-wave tube

A cylindrical waveguide, provided with wedge-shaped metal vanes projecting radially inward from the wall of the guide, excited in the transverse electric (TE) mode, was analysed. The analysis was carried out considering the angular harmonics generated by the angular positioning of the vanes. A set of equations was generated in the Fourier amplitudes of field constants. The condition for nontrivial solutions for the field constants gave the dispersion relation of the structure. From the expression of power flow down the structure, its interaction impedance was also estimated. The shape of the dispersion characteristics and the value of the cutoff frequency as well as the interaction impedance characteristics of the waveguide were found to depend on the vane parameters their number as well as their radial and angular dimensions. The optimum vane parameters were obtained corresponding to the minimum variation of the slope of the ω-β dispersion plot, such parameters being useful from the standpoint of the bandwidth of a gyro-travelling-wave tube (gyro-TWT) using a vane-loaded cylindrical waveguide as the interaction structure. The dispersion and impedance characteristics, which were found typically for the TE₀₁ mode as defined for the structure, taking four vanes, were more sensitive to the number and angular width of the vanes than to their radial depth. The value of the interaction impedance, calculated at the potential beam position, was found to be higher for a loaded waveguide than for an unloaded one, and it depended on the frequency of operation relative to the cutoff. The interaction impedance also depended on the position of the beam relative to the waveguide wall where it was estimated, and hence the optimum beam position corresponding to the maximum interaction impedance was found. The theory was validated against the dispersion characteristics reported elsewhere typically for four-vane magnetron-like structures excited in the 2π mode. Although the present study was restricted to ‘cold’ analysis of the structure in the absence of the electron beam, it could provide important feedback for analysing a gyro-TWT, using a vane-loaded cylindrical waveguide, and hence for predicting the structure parameters for the wide-band performance of the device.     

Analysis of Helix Slow Wave Structure for High Efficiency Space TWT

This paper describes the analysis of helix slow-wave structure (SWS) for a high efficiency space traveling wave tube that is carried out using Ansoft HFSS and CST microwave studio, which is a 3D electromagnetic field simulators. Two approaches of simulating the dispersion and impedance characteristics of the helix slow wave structure have been discussed and compared with measured results. The dispersion characteristic gives the information about axial propagation constant (Beta). Which in turn yields the phase velocity at a particular frequency. The dispersion and impedance characteristics can be used in finding the pertinent design parameters of the helix slow-wave structure. Therefore a new trend has been initiated at CEERI to use Ansoft HFSS code to analysis of the helix slow wave structure in its real environment. The analysis of the helix SWS for Ku-band 140W space TWT has been carried out and compared with experimental results, and found is close agreement.     

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.     

Equivalent Circuit Analysis of Serpentine Folded-waveguide Slow-wave Structures for Millimeter-wave Traveling-wave Tubes

A simple equivalent circuit model for the analysis of dispersion and interaction impedance characteristics of serpentine folded-waveguide slow-wave structure was developed by considering the straight and curved portions of structure supporting the dominant TE ₁₀-mode of the rectangular waveguide. Expressions for the lumped capacitance and inductance per period of the slow-wave structure were derived in terms of the physical dimensions of the structure, incorporating the effects of the beam-hole in the lumped parameters. The lumped parameters were subsequently interpreted for obtaining the dispersion and interaction impedance characteristics of the structure. The analysis was simple yet accurate in predicting the dispersion and interaction impedance behaviour at millimeter-wave frequencies. The analysis was benchmarked against measurement as well as with 3D electromagnetic modeling using MAFIA for two typical slow-wave structures (one at the Ka-band and the other at the W-band) and close agreement observed.     

A simple equivalent circuit analysis of rectangular folded-waveguide slow-wave structure

A simple yet accurate equivalent circuit model was developed for the analysis of slow-wave properties (dispersion and interaction impedance characteristics) of a rectangular folded-waveguide slow-wave structure. Present formulation includes the effects of the presence of beam-hole in the circuit, which were ignored in existing approaches. The analysis was benchmarked against measurement as well as with 3D electromagnetic modeling using MAFIA for two typical slow-wave structures operating in Ka- and Q-bands, and close agreements were observed. The analysis was extended for demonstrating the effect of the variation of beam-hole radius on the RF interaction efficiency of the device.     

苜蓿叶形耦合腔慢波结构的模拟和验证

苜蓿叶形耦合腔慢波结构是一种高耦合阻抗的慢波线。由于结构复杂,其数学分析及工程设计都非常困难。该文利用三维电磁计算软件Isfel3d,Mafia,HFSS对这种结构的色散特性、耦合阻抗进行数值模拟,在分析模拟结果的基础上,对这种结构做了初步的优化。结果表明,数值模拟与实验结果有很好的一致性,这对改进这种慢波线的工程设计具有重要意义。     

A Simple and Accurate Analysis of Conductivity Loss in Millimeter-Wave Helical Slow-Wave Structures

Electromagnetic field analysis of a helix slow-wave structure was carried out and a closed form expression was derived for the inductance per unit length of the transmission-line equivalent circuit of the structure, taking into account the actual helix tape dimensions and surface current on the helix over the actual metallic area of the tape. The expression of the inductance per unit length, thus obtained, was used for estimating the increment in the inductance per unit length caused due to penetration of the magnetic flux into the conducting surfaces following Wheeler’s incremental inductance rule, which was subsequently interpreted for the attenuation constant of the propagating structure. The analysis was computationally simple and accurate, and accrues the accuracy of 3D electromagnetic analysis by allowing the use of dispersion characteristics obtainable from any standard electromagnetic modeling. The approach was benchmarked against measurement for two practical structures, and excellent agreement was observed. The analysis was subsequently applied to demonstrate the effects of conductivity on the attenuation constant of a typical broadband millimeter-wave helical slow-wave structure with respect to helix materials and copper plating on the helix, surface finish of the helix, dielectric loading effect and effect of high temperature operation – a comparative study of various such aspects are covered.     

Study on the Characteristics of the Rib-Loaded Disk-Loaded Waveguide

The disk-loaded waveguide with bandwidth of only 2%-8% is a kind of narrow band structure. A new rib-loaded disk-loaded waveguide with wider bandwidth than the general one is suggested in the paper. The author develops the method of calculating the axial periodic waveguide by expanding the slow-wave structure's boundary function in Fourier series, so that it can be adopted in rib-loaded disk-loaded waveguide. By the method, the dispersion characteristics and interaction impedance of a Ka band rib-loaded disk-loaded waveguide are analyzed.     

Diamond-studded helical traveling wave tube

A novel method of millimeter-wave traveling wave tube (TWT) slow-wave circuit fabrication, employing laser micromachining and the in situ growth of diamond studs as an insulating dielectric, has been developed, which would enable a new class of very wideband, low distortion, high-efficiency amplifiers. Because the slow-wave circuit is supported by an array of diamond studs, rather than the conventional dielectric rods, we have named this novel device the diamond-studded TWT. Diamond strips have been successfully grown on a molybdenum tube and a diamond-studded helix has been produced using laser micromachining. Computer analysis of the slow-wave structure indicate that this fabrication technique leads naturally to a circuit with nearly flat dispersion over a frequency range, in some configurations, of more than four octaves. Typically, wide bandwidth can only be achieved by reducing efficiency; however, this fabrication technique increases the interaction impedance of the circuit, enabling high efficiency operation without sacrificing bandwidth. The very low dispersion also results in a coupling impedance that is relatively insensitive to frequency that may enable low reflection coupling over a wide frequency band. The resulting slow-wave circuit is essentially a brazed structure and, therefore, inherently robust thermally and mechanically. The manufacturing technology being pursued is applicable to any millimeter-wave helical or helix-derived TWT.     

Parametric Simulation and Optimization of Cold-test Properties for a 220 GHz Broadband Folded Waveguide Traveling-wave Tube

Characterized with full-metal structure, high output power and broad bandwidth, microfabricated folded waveguide is considered as a robust slow-wave structure for millimeter wave traveling-wave tubes. In this paper, cold-test (without considering the real electron beam) properties were studied and optimized by 3D simulation on slow-wave structure, for designing a 220 GHz folded waveguide traveling-wave tube. The parametric analysis on cold-test properties, i.e., phase velocity, beam-wave interaction impedance and cold circuit attenuation, were conducted in half-period circuit with high frequency structure simulator, assisted by analytical model and equivalent circuit model. Through detailed parametric analyses, interference between specified structural parameters is found on determining beam-wave interaction impedance. A discretized matrix optimization for interaction impedance was effectively carried out to overcome the interference. A range of structural parameters with optimized interaction impedance distributions were obtained. Based on the optimized results, a broadband folded waveguide with cold pass-band of about 80 GHz, flat phase velocity dispersion and fairly high interaction impedance was designed for a 220 GHz central frequency traveling-wave tube. A three-dB bandwidth of 20.5 GHz and a maximum gain of 21.2 dB were predicted by small signal analysis for a 28 mm-long lossy circuit.     

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.     

Nonresonant perturbation measurements on dispersion and interactionimpedance characteristics of helical slow-wave structures

A nonresonant perturbation (NRP) theory is developed from first principles for the measurement of dispersion and interaction impedance characteristics of a helical slow-wave structure (SWS). The phase of the reflected signal from a test helical structure varies when a perturber, also in the form of a helix, is moved along the axis of the test structure. The variation of phase with perturber position is interpreted to find the phase velocity of the structure under test. The interaction impedance of the structure is found by measuring the change in the axial phase-propagation constant of the structure as a dielectric rod is placed along the axis of the structure. Measurements are carried out with the help of an automated setup using an HP 8510 vector network analyzer (VNA) and a PC to collect the phase informations for the various precisely controlled positions of the perturber using a stepper motor, which is also interfaced with the PC. The experimental and theoretical values of the phase velocity and the interaction impedance of a typical “cold” experimental helical structure for a wide-band TWT are found to be close within 0.5% and 5%, respectively, in an octave band of 8-16 GHz     

螺旋线慢波结构的参数变化对其冷测特性的影响

本文介绍了用MAFIA软件的准周期边界条件计算螺旋线行波管慢波结构的色散和耦合阻抗等冷测特性的方法,并重点对慢波结构中各参数,特别是矩形螺旋线截面的宽度和厚度对其冷测特性的影响进行了分析.这是目前理论上没有解决的难题.分析结果表明,螺旋线的宽度和厚度对其色散影响不大,而对耦合阻抗有一定影响.对耦合阻抗而言,螺旋带宽度和厚度都存在一个最佳值.     

Study of Corrugated Elliptical Waveguides for Slow-Wave Structures

The slow-wave characteristics taking account of space harmonics for confocal corrugated elliptical waveguides are presented. By using the field-matching method, the dispersion equation, and the mean interaction impedance for odd hybrid modes of this structure are derived. Based on our results, changing the waveguide eccentricity can improve the dispersion characteristics and the interaction impedance for _oEH₀₁ mode