Sensitivity analysis of TWT's small signal gain based on the effectof rod shape and dimensions

An extensive study aiming at analyzing the effect of rod shapes and dimensions on the gain of helix traveling wave tubes (TWTs) is performed. The evaluation of tube small-signal gain is obtained by making use of a rigorous field analysis which takes into account the helix tape model and the dielectric inhomogeneous loading conditions. Computing time to perform the analysis is extremely low compared with the time required in the case of a full wave, three-dimensional (3-D) electromagnetic simulator. The accuracy of the simulation approach has been extensively verified in a previous paper. A novel expression for the attenuation constant has been introduced in the model to improve the quality of results. The proposed study allows a better understanding of tube behavior before fabrication highlighting the contribution of the shape, the mechanical tolerances and the ϵ_r variation of the rods to the small-signal gain     

Polarization dependent loss induced gain ripple statistics inerbium-doped fiber amplifiers

A Monte-Carlo model is used to simulate the wavelength-dependent polarization dependent loss (PDL) statistics and PDL induced gain-ripple statistics for a chain of concatenated optical elements in an erbium-doped fiber amplifier (EDFA). Simulations indicate that unlike polarization-mode dispersion (PMD), the quadrature sum of PDL overestimates the mean of the PDL distribution. We show that EDFA total PDL variance scales linearly with the individual component PDL variance. Moreover, the relative impact of PDL on the gain ripple is reduced in the presence of the PDL independent gain ripple in the EDFA     

Calculating the Raman pump distribution to achieve minimum gain ripple

A procedure is presented for calculating the optimum Raman pump wavelengths and powers for a discrete set of lasers and for a pump continuum. Theoretical results in the continuum case shown that broad-band gain with extremely low ripple can be obtained.     

Semianalytical approach to the gain ripple minimization in multiple pump fiber Raman amplifiers

A simplified approach to the search of Raman pump powers and wavelengths minimizing the gain ripple in a Raman multiple-pump amplifier is presented. The first step is to evaluate the pump path average powers and the wavelengths through a minimization algorithm. Then, an approximated analytical derivation of the initial pump powers, that yields an approximated path average power, is given. The results of the algorithm are in excellent agreement with the full numerical calculations.     

Quasi-three-dimensional perturbation technique, includingdielectrics for TWT's

A perturbation technique is described for finding phase velocities and coupling impedances in a traveling wave tube for an arbitrary distribution of dielectric material. A model of the sheath helix is presented. Tape helix results will be presented in a separate paper. In all cases presented, without adjusting the dielectric constant, the calculated perturbed phase velocity provided a better answer than the homogeneous dielectric solution, or Naval Research Laboratories' Small Signal Gain Program. Deviation from theory versus experiment is reported by stating the average sum of the squares difference between theoretical calculations and a second order least squares fit of the measured data. Phase velocities can be calculated for uniform dielectric support rods where the average sum of the squares ⩽1.19×10^-5. For cases with notched dielectric support rods phase velocities can be calculated where the average sum of the squares ⩽1.94×10^-5. For NRL's SSG program the average sum of the squares was ⩽1.01×10^-4 by comparison. For uniform dielectric support rods the perturbation does not significantly alter the basic shape of the predicted dispersion curve. For notched dielectric support rods applying the perturbation does alter and flatten the shape of the predicted dispersion curve in agreement with experiment     

Use of a simple external nonreciprocal attenuator in coupled-cavity TWT's

It is well known that use of a nonreciprocal sever in traveling-wave tube (TWT) design offers several advantages. Previous attempts to obtain these advantages involved incorporation of ferrite material within the envelope of helix TWT's. These attempts have encountered serious difficulties, and have had no apparent effect on TWT design practice. A different approach to realization of a nonreciprocal sever for a coupled cavity TWT is described. This approach involves readily available wave guide components external to the tube, and does not appear to require the solution of significant research and development problems. A computer simulation performed on the CTS 200 W TWT design indicates that a substantial improvement in efficiency could be obtained through use of this technique.     

Comments on measuring the overall and the depressed collector efficiency in TWT's and Klystron amplifiers

Evaluation procedures for multistage depressed collectors are discussed and sources of possible errors are pointed out. The errors may inflate the computed collector efficiences by as much as 10 percentage points.     

螺旋线行波管慢波结构热特性计算专用软件开发

针对行波管慢波结构热分析的必要性,介绍了螺旋线慢波结构的热产生机理,结合ANSYS软件设计了可对不同翼片加载和不同形状夹持杆的螺旋线慢波结构进行热特性分析的专用仿真环境。利用该仿真环境,用户可以在不掌握ANSYS软件的情况下对螺旋线行波管慢波结构的热特性进行模拟计算。     

Computation of matching characteristics between rectangular coupled cavity and waveguide for millimeter wave TWT's

A rectangular coupled cavity slow wave structure is a new type of circuit for high power millimeter wave TWTs in recent years. Matching characteristics of trasition between rectangular coupled cavity and waveguide are calculated by equivalent circuit method. The results obtained by this method are compared with experiments and it is shown that useful accuracy can be obtained.     

Minimization of torque ripple in SRM drives

The torque pulsations in switched reluctance motors (SRMs) are relatively higher compared to sinusoidal machines due to the doubly salient structure of the motor. The magnetization pattern of the individual phases together with the T-i-&thetas; characteristics of the motor dictate the amount of torque ripple during operation. Both machine design and electronic control approaches have been used to minimize the torque ripple in SRMs. This paper presents an extensive review of the origin of torque ripple and the approaches adopted over the past decade to minimize the torque ripple. A hybrid torque-ripple-minimizing controller that incorporates the attractive features of some of the techniques developed in the past decade is presented along with simulation and experimental results     

Metrics for dispersion ripple in optical systems

An analysis of the relationship between group delay ripple and eye closure penalty is used to develop two metrics that parameterise signal degradation due to optical filter group delay ripple. These metrics, which are based upon the standard deviation of the group delay ripple, correlate very well with the signal eye closure penalty. The metrics provide an upper and lower limit to the eye closure penalty applicable over a wide range of group delay ripple amplitudes and pitches as well as bit rates.     

基于纹波注入滤波方案的超小纹波开关电源设计

各种电子设备的正常运行都离不开电源,电源的主要技术指标的优劣直接决定着整个电子设备的性能。例如,对于智能电能表电源来说,输出纹波就是一个尤为重要的指标。本文采用纹波注入滤波方案,设计了一款性价比高的超小纹波开关电源。     

电源纹波的测量和抑制

本文介绍了电源电压纹波和纹波系数的概念.提出四种抑制电源纹波的方法:RLC滤波法、共模滤波法、铁氧体磁环滤波法以及组合滤波法.通过实验得到四种方法的滤波效果,并总结了它们的优缺点.通过比较得出,使用组合滤波方法可以有效降低电源纹波.     

离子波纹场纵向电场分量对离子波纹激光的影响

通过非线性数值模拟，研究了离子波纹激光（ＩＲＬ）中离子波纹场的纵向电场分量对束－波互作用的影响。结果表明，离子波纹场的纵向分量对ＩＲＬ的工作状况具有较大的影响。其中互作用长度的选择是非常重要的     

COCA: a novel 3-D FE simulator for the design of TWT's multistagecollectors

In this paper, the simulator COCA, a novel fully three-dimensional (3-D) finite-element (FE) tool for the design of multistage depressed TWTs collectors is illustrated. COCA has been developed at the University of Catania under an ESA/ESTEC project. The complete simulator consists of three main modules: a fully 3-D deterministic/neural FE mesh generator, an FE Vlasov solver coupled with an electron trajectory tracer taking into account also external magnetic fields, and a postprocessing module for result restitution, including secondary electron emission effects. All the functions are interactively managed and executed by means of an especially developed user-friendly graphical user interface which controls all the various aspects of a simulation session. The results of a simulation test performed on an asymmetric collector are also reported showing excellent agreement with available measured data. The COCA simulator provides the user with flexible and effective tools to design, test, optimize, and verify innovative asymmetrical geometries for TWT collectors     

A solution to the problem of spontaneous deflection of the beam in TWT's with low helix voltage

The spontaneous deflection of the beam in low voltage, typically low noise, traveling-wave tubes has been studied and attributed to the accumulation of stray charges on the glazed helix rods. A means of measuring the tendency of the helix to show these charging effects will be described. A method of processing of the complete helix which prevents the accumulation of charges but does not seriously affect its cold loss or other microwave properties will be reviewed. Traveling-wave tubes that have been made with helices processed by this technique cannot be made to show charging effects or beam deflections. Six tubes have accumulated 22,000 tube hours with no failures.     

Gain ripple minimisation and higher-order modes in semiconductor optical amplifiers

Theoretical results are presented about the gain ripple performance of various structures proposed to obtain true travelling-wave operation in optical semiconductor laser amplifiers. Higher-order transverse modes are shown to limit the efficiency of antireflection mechanisms, especially in the case of misaligned stripes.<>     

开槽深度和坡度对高频高阶模带宽和中心频移的影响

为对构建太赫兹频率下高阶单模工作的同轴布喇格谐振腔提供理论依据,基于模式耦合理论,比较研究了不同开槽深度和不同开槽坡度形状及坡度角对工作在太赫兹频率高频高阶耦合模式下工作模式和竞争模式带宽、中心频率偏移特性的影响. 结果表明:工作模式和竞争模式的带宽随着开槽深度的加深都变宽,但中心谐振频率点几乎没有偏移,槽深加深,带隙重叠现象会恶化,不利于模式选择;正圆锥形坡度方式时随着坡度角的增加,工作模式的中心频率点没有发生偏移,竞争模式中心频率点靠近工作模式中心频率点,不利于带隙重叠现象的抑制;倒圆锥形坡度方式时,随着坡度角的增大,竞争模式的中心频率点远离工作模式中心频率点,很好地抑制了带隙重叠;正圆锥形坡度和倒圆锥形坡度对带宽的影响都不大. 这些特性有利于拓展同轴布喇格结构作为反射器和滤波器的性能.