D波段行波管三级降压收集极的设计

效率是行波管(TWT)的重要技术指标,为提高某一0.22 THz折叠波导行波管的效率,需设计多级降压收集极。对注波互作用后的电子注信息进行分析,估算收集极效率最高时的电压设置。利用电磁仿真软件对三级降压收集极电极结构和电压设置进行仿真优化,得到效率大于87.5%,回流电流小于0.328 9 mA的轴对称三级降压收集极;在第二电极入口采用斜口结构进行仿真优化,得到回流电流小于0.075 mA的非轴对称三级降压收集极。结果表明,采用斜口结构可以有效降低0.22 THz行波管多级降压收集极的回流电流。     

多级降压收集极中次级电子的研究

效率与电子回流率是考核多级降压收集极的重要指标,而多级降压收集极中次级电子的存在对效率和电子回流率有重要影响.因此,对次级电子的研究有重要意义.本文探讨了次级电子发射的物理原型,并根据其编制了相应的CAD程序, 在对多级降压收集极的试算中,取得了较好的效果.     

多级降压收集极行波管高压电源的设计

为了提高真空管雷达发射机的效率、缩小整机的体积和重量,常使用多级降压收集极行波管作为功率射频放大器.为了保证多级降压收集极行波管高增益、高效率和良好线性等性能发挥的更好,就要在行波管每个电极上加合适的电压,确保行波管内建立稳定的电场.因此,根据行波管各电极的特性合理地选择各收集极的电压以及合理的设计高压电源显得尤其重要.文中结合多级降压收集极行波管的工作特性介绍了4种高压电源的设计方法及其特点.     

多级降压收集极CAD中的二次电子发射模型

多级降压收集极被广泛应用于提高微波放大器件效率.多级降压收集极中的二次电子发射对其效率有重要影响.该文探讨了真二次电子、弹性反射电子、非弹性反射电子3种二次电子发射模型,对发射率、发射角度以及能量分布情况进行了深入分析,并对考虑二次电子后的收集极模拟计算收敛条件进行了讨论.上述结果在多级降压收集极CAD软件中得到应用,定量分析了其对多级降压收集极效率的影响.     

多级降压收集极的模拟仿真软件

研制了一个微波管多级降压收集极的二维模拟计算软件MSDC。MSDC软件采用圆柱坐标系，计算静电场分布、注入的原电子的运动轨迹、原电子撞击电极引发的次级电子的发射和运动轨迹、电子运动形成的空间电荷密度等，最后给出多级压收集极的性能。本软件还具备再聚焦区电子注层流性计算功能，以便指导再聚焦区磁场分布的优化。本软件的主要特点，是考虑了次级电子的空间电荷效应，每次迭代计算、原电子轨迹和次级电子轨迹的影响全都包括进去。     

用于倍频程带宽、高性能行波管的小型、81～83.5％效率的2级和4级降压收集极

在美国空军(USAF)——国家航宇局(NASA)共同制定的规划中,Lewis研究中心正在进行电子对抗行波管效率的改进工作,它是通过采用多级降压收集极(MDC)以及在该中心所探索的对耗能电子注的再聚焦技术来实现的。在本规划的分析阶段,计算了整个行波管的三维电子注轨迹。轨迹计算一直到耗能电子注的再聚焦区和降压收集极。对收集极效率、收集极损耗和管子总效率进行了验证和计算。在实验工作方面,首先对不用多级降压收集极的管子性能进行估测,然后对耗能电子注的对称性、圆度和速度离散作了分析。最后,装上了多级降压收集极,使其性能最佳并进行了估测。对于理想的行波管,三维理论表明:具有对称、圆型并有最佳再聚焦电子注的2级多极降压收集极在中心频带有81％的效率(多级降压收集极),而4级多级降压收集极有85％的效率。实验结果所获得的数据表明:一个倍频程带宽——(4.8～9.6)千兆赫、功率为330～550瓦行波管的2级和4级降压收集极的最小多级降压收集极效率分别为81％和83％。     

行波管多级降压收集极CAD软件研究与实现

该文讨论了行波管多级降压收集极CAD理论模型,在二维轴对称条件下,对网格自动划分技术、二次电子发射模型、空间电荷效应计算方法、外加磁场影响、收集极效率计算方法等进行了深入研究,并在现有模型基础上进行了修改,以获得更好的模拟效果。同时在此基础上,开发了行波管多级降压收集极CAD软件UESTC_MDC,并对该软件的使用进行了简单的介绍。最后根据国外研究发展动向,对我国行波管多级降压收集极CAD软件的发展提出了一些可参考的意见和建议。     

多注行波管收集极的设计与模拟

多级降压收集极是提高行波管效率的有效途径,本文在粒子算法的基础上,编写了多注行波管收集极的专用软件,实现了电子收集的三维模拟,计算结果与二维程序进行了比较,并利用该软件设计模拟了一个五注行波管两级降压收集极,对计算结果进行了分析。     

多级降压收集极入口电子速度分布研究与应用

研究了多级降压收集极入口电子速度分布理论,并设计实验获取了入口电子能量分布密度函数。利用能量分布密度函数构造比较真实的收集极仿真初始条件,仿真结果与实测数据有很好的一致性。较旧的仿真初始条件仿真结果有很大改善,为多级降压收集极的设计和优化提供了有效依据,从而提高行波管的效率。     

行波管多级降压收集极的计算和实验研究

采用多级降压收集极是提高行波管效率析有效途径之一。本文在ＳＬＡＣ－２６６程序的基础上对一支带有二级降压收集极的国外行波管进行了计算,并且将计算结果同实验结果进行了比较。同时用电子注分析仪对降压收集极区电子注和纵向速度分布进行了实验研究,获得了该二级降压收集极的部分工作曲线,并对实验结果进行了分析讨论。     

Verification of an improved computational design procedure for TWT-Dynamic refocuser-MDC systems with secondary electron emission losses

A computational procedure for the design of TWT-refocuser-MDC systems was used to design a short "dynamic" refocusing system and highly efficient four-stage depressed collector for a 200-W 8-18-GHz TWT. The computations were carried out with advanced multidimensional computer programs which model the electron beam as a series of disks of charge and follow their trajectories from the RF input of the TWT, through the slow-wave structure and refocusing section, to their points of impact in the depressed collector. Secondary emission losses in the MDC were treated semiquantitatively by injecting a representative beam of secondary electrons into the MDC analysis at the point of impact of each primary beam. A comparison of computed and measured TWT and MDC performance showed very good agreement. The electrodes of the MDC were fabricated from a particular form of isotropic graphite that was selected for its low secondary electron yield, thermal expansion characteristics, ease of machinability, and vacuum properties. This MDC was tested at CW for more than 1000 h with negligible degradation in TWT and MDC performances.     

Experimental verification of a computational procedure for the design of TWT-refocuser-MDC systems

A comparison of analytical and experimental results is presented for a high performance dual-mode helix TWT, equipped with multistage depressed collectors (MDC), and operated over conditions ranging from saturation to the linear regime. The computations are carried out with advanced multidimensional computer programs which model the electron beam as a series of disks or rings of charge and follow their trajectories from the RF input of the TWT, through the slow-wave structure, through the refocusing system, to their points of impact in the depressed collector. Twr performance, collector efficiency, and collector current distribution are computed and compared with measurements. Very good agreement is obtained between computed and measured TWT performance and collector efficiencies. The analytical techniques were subsequently applied to the design of a smaller MDC of nearly equal efficiency.     

Small-size 81- to 83.5-percent efficient 2- and 4-stage depressed collectors for octave-bandwidth high-performance TWT's

In a joint USAF-NASA Program, Lewis Research Center is carrying out an efficiency improvement program on traveling wave tubes (TWT) for use in electronic counter measures (ECM) by applying multistage depressed collector (MDC) and spent beam refocusing techniques developed at Lewis. In the analytic part of the effort, three-dimensional electron trajectories are computed throughout the TWT. Trajectory computation continues through the spent beam refocuser and the depressed collector. Collector efficiency, collector losses, and overall efficiency are identified and computed. On the experimental side, tube performance is evaluated first without the MDC; then, the spent beam is analyzed for symmetry, circularity, and velocity spread. Finally, the MDC is attached and its performance optimized and evaluated. The three-dimensional theory, for ideal tubes, predicts a MDC-efficiency, at mid-band, of 81 percent for a 2-stage MDC with symmetric, circular, and optimally refocused beams and 85.5 percent for a 4-stage MDC. Experimental results to date have yielded MDC efficiencies of a minimum of 81 and 83 percent for a 2- and 4-stage MDC, respectively, across a one-octave bandwidth of a 4.8 to 9.6 GHz 330-to-550-W TWT.     

多级降压收集极效率的优化

围绕着MDC的核心即提高效率问题,分析了MDC的物理模型,阐明了MDC的功率分布图并解释了其来源.利用MDC的入口条件生成的功率分布图,可以快速得到给定降压级数的MDC的最优化效率,以及各电极的最优化电位.在最优化电位附近进行模拟仿真,减小电位选择的盲目性,起到事半功倍的效果.     

具备调焦功能的空间光学载荷支撑结构设计(特邀)

由于空间环境变化,高分辨率空间光学载荷在轨会产生不同程度的离焦从而影响成像质量,因此需要进行在轨调焦。为了适应高分辨率、轻小型空间光学载荷发展需求,设计了一种集支撑功能、调焦功能为一体的结构,通过热控系统对支撑结构温度的精准控制来调整次镜组件在光轴方向的位置,从而使载荷具备调焦功能。首先,根据光学系统参数进行调焦精度分析,确定支撑结构的设计要求;然后,基于连续拓扑优化中的变密度法(SIMP)进行支撑结构的全局优化;最后,开展了热光学试验,验证支撑结构的热控调焦功能并测量热控调焦系数。试验结果表明:该光学载荷支撑结构热控调焦系数为0.071 mm/℃,可实现0.014 mm调焦精度和±0.385 mm调焦范围。基于该调焦方法设计的“吉林一号”高分03星已经完成在轨测试,调焦精度和调焦范围满足设计预期。     

基于DaVinci技术数字对焦重构算法研究与实现

数字对焦光场成像技术是一种新型的计算成像技术,利用光学手段获取四维光场信息,通过重构二维空间信息和一维深度信息,达到先拍摄后对焦的目的。研究光场图像数字对焦重构算法,利用TI公司推出的DaVinci系列处理器DM6467对数字对焦重构算法进行硬件仿真,通过改变对焦系数,得到不同深度的对焦图像。同时,根据C64x+DSP核的特点,通过循环分解、项目级优化等方法对代码进行一定的优化,使代码执行效率提高了18倍左右,对实现光场成像系统的小型化和实时化具有重要的指导意义。     

SAR图像中运动目标重聚焦改进的最小熵方法

合成孔径雷达(Synthetic Aperture Radar,SAR)利用回波多普勒(Doppler)频移生成高分辨率的SAR图像。高速运动的目标产生额外的多普勒频移,在SAR图像上会呈现出带有拖曳尾迹的散焦图像。最小熵方法是一种无参数的优化方法。该文以图像的信息熵为目标函数,对最小熵方法的优化算法进行了改进,加快该方法对于目标重聚焦的实现速度。该文中用模拟的飞行目标散焦图像进行最小熵优化实现重聚焦,为在SAR图像中快速识别模糊散焦的运动目标提供了一种应用方法。     

Analysis of macroscopic diversity combining of MIMO signals in mobile communications

In this paper, the system model and performance analysis of macroscopic diversity combining (MDC) multiple-input multiple-output (MIMO) systems are presented for mobile cellular communication applications. The channel capacity of MIMO systems will deteriorate if the dual antenna array (DAA) spacing is insufficient or the scattering environment does not provide completely uncorrelated channels. In addition, the shadowing component of the directional signal is a common factor among the scattered channels, resulting in significant reductions in obtainable channel capacity. Therefore, in this paper, a macroscopic diversity topology is applied to maximize the spatial multiplexing gain while combating the shadowing phenomena. The channel capacity as well as its upper and lower bounds are derived for MIMO-based MDC systems. Additionally, the outage capacity for the proposed MDC system topology has been analyzed. Compared to a single communicating MIMO system pair, the results show that the macroscopic diversity MIMO communication topology enables a larger number of uncorrelated shadowed and scattered channels to exist, and therefore, improvements of enhanced channel capacity and reduced outage is obtained.