The 1976 S-MTT National Lectureship

Remarkable progress is being made in improving the performance of microwave solid-state devices used for signal processing and power generation. As a result, microwave solid-state amplifiers and oscillators are replacing low-noise and medium-power traveling-wave tubes (TWT's) and backward-wave oscillators (BWO's), and entirely new applications for microwave technologies are being created.     

Harmonic generation in octave bandwidth traveling-wave tubes

This paper describes the investigation of harmonic generation in traveling-wave tubes (TWT's) via large-signal analysis and digital computer techniques. Efficiency degradation and harmonic power content are shown to be importantly related to such TWT design considerations as circuit dispersion, harmonic coupling impedance ratio, and gain level. Also described is the phenomenon of second harmonic interference in the beam bunching process and how it leads to substantial efficiency reduction in TWT's employing relatively nondispersive structures.     

Accurate Calculation of TWT Intermodulation in the Many-Carrier Case

The formulas derived by Stette [1] permit the calculation of TWT output carrier power and intermod power when the input to the TWT consists of an infinite number of infinitesimal carriers. The formulas for these quantities involve an integration of the TWT singlecarrier characteristic over a semi-infinite range, and for most of the TWT's one considers, a simple approximation of the integration by a summation gives satisfactory answers. However, when one considers special TWT's, e.g., linearized TWT's or the piecewise linear limiter [2], simple approximations are often not good enough. To get accurate results, a multipoint Gaussian quadrature must be used.     

利用CST微波工作室软件改进行波管的性能

计算机辅助设计（CAD）是设计行波管（TWT）的关键一步。本文介绍了利用CST微波工作室软件计算行波管慢波结构的色散和耦合阻抗的原理和方法。并用计算机模拟仿真行波管慢波结构冷特性，结合实际制管，提高了行波管的性能。     

Traveling wave tubes for communication satellites

Traveling wave tubes (TWT's) have contributed markedly to the development of communications satellites. As the prime-power consuming and transmitting device, the major transponder gain element, and the largest contributor to transmission nonlinearities, the TWT has been the focal point for continuous but carefully measured evolutionary improvements. Efficiency improvements continue to be made without compromising desired communications characteristics or tube lifetimes. These improvements have been made primarily in the RF circuit through loss reduction and phase-velocity tapering techniques, and in the spent-beam region through better multielement collector designs. Traveling wave tubes developed for satellites at 4 and 12 GHz are used as examples. Since TWT's ate life-limited devices, emphasis has been placed on techniques ensuring long life in satellite applications. Both oxide- and dispenser-type cathodes are discussed and data on life characteristics are presented. During the past decade, while generally demonstrating excellent space lifetimes, operating TWT's continue to approach their potential cathode wear-out life, which is theoretically of the order of 10⁵h.     

Gain stability of traveling wave tubes

The long-term gain stability of traveling wave tubes (TWT's) with helix slow-wave structures is examined. A major variable in the gain of TWT's is the stability of the attenuator material that is placed in the tube to damp oscillations and improve input-to-output isolation. Thin carbon layers are often used for this purpose in TWT's and are deposited onto the helix support rods by several different techniques that produce a variability in the material structure and properties. The carbon layers are also susceptible to physical damage due to the environment in the tube during conditioning and long-term operation. Modification of the electrical conductivity of the layer by energetic particle bombardment and chemical erosion decreases the net RF loss in the tube and causes the gain to increase with time. The presence of impurity gases and rapid conditioning procedures produce gain increases due to the lattice damage of the attenuator material of up to 10 dB in a TWT in the first several hundred hours of operation. Properly designed attenuator loss-patterns and minimization of the gas evolution in the TWT causes these effects to saturate and the gain to stabilize quickly. Techniques to ensure long-term stability of these layers are discussed     

毫米波折叠波导行波管的研究

采用等效电路方法和电磁场仿真软件Ansoft HFSS分析了折叠波导行波管的结构参数对其高频特性的影响,并在此基础上确定了Ka波段折叠波导行波管的尺寸.利用三维非线性粒子模拟软件MAGIC3D建立了两段式折叠波导行波管的模型,模拟研究了切断区长度和位置对折叠波导行波管的饱和输出功率及第2段电路单位长度增益的影响.最后设计了一个工作于33～36GHz的两段式折叠波导行波管,其输出功率的波动小于1dB,最大连续波输出功率达670W,对应电子效率高达7.55％.     

NLA-QAM: A Method for Generating High-Power QAM Signals Through Nonlinear Amplification

A generalized technique for generating quadrature amplitude modulated (QAM) signals that permits nonlinear amplification is presented. With this technique a high-power2^{2n}-state QAM signal is generated by combiningnunfiltered, nonlinear amplified, QPSK signals,nbeing a positive integer. The specific methods of generating 16- and 64-state signals using this technique are presented. An attractive feature of the technique is that despite significant difference with the conventional method of generating QAM signals, the same straightforward demodulation techniques apply to both, and the PeversusS/Nperformances are essentially identical. In the 16-state version employing traveling wave tubes (TWT's) or GaAsFET amplifiers, the technique is shown to result in a transmitter output power advantage that is on the order of 5 dB compared to the conventional method. This advantage is achieved, however, at the expense of an additional output power amplifier.     

Traveling-wave tubes with ferrite attenuators

In order to determine the efficacy of ferrite isolators used as internal attenuators in traveling-wave tubes, two TWT's incorporating such isolators were developed, one using orthodox magnetic focusing, the other using electrostatic focusing. The results of the experimentation indicate that the ferrite can, in some cases, offer improvement in gain and efficiency over reciprocal attenuators. The limitations of this device are discussed together with some particular advantages it may offer for special applications. Design criteria for such isolators and the effects of the ferrite as a circuit element in TWT's, are also investigated.     

Simulation of cold-test parameters and RF output power for acoupled-cavity traveling-wave tube

Procedures have been developed which enable the accurate computation of the cold-test (absence of an electron beam) parameters and RF output power for the slow-wave circuits of coupled-cavity traveling-wave tubes (TWT's). The cold-test parameters, which consist of RF phase shift per cavity, impedance, and attenuation, are computed with the three-dimensional electromagnetic simulation code MAFIA and compared to experimental data for an existing V-band (59-64 GHz) coupled-cavity TWT. When simulated in cylindrical coordinates, the absolute average differences from experiment are only 0.3% for phase shift and 2.4% for impedance. Using the cold-test parameters calculated with MAFIA as input, the NASA Coupled-Cavity TWT Code is used to simulate the saturated RF output power of the TWT across the V-band frequency range. Taking into account the output window and coupler loss, the agreement with experiment is very good from 60-64 GHz, with the average absolute percentage difference between simulated and measured power only 3.8%. This demonstrates that the saturated RF output power of a coupled cavity TWT can be accurately simulated using cold-test parameters determined with a three dimensional electromagnetic simulation code     

Reflexions and gain ripple in TWT's

The presence of the electron beam in a TWT introduces additional internal reflexions that are not present in the cold tube, at the output, at the input, and at the attenuator. These additional reflexions, that we denote "electronic reflexions,"increase the gain ripple. The electronic reflexions are hard to measure and therefore have to be calculated. In the present paper, equations are derived for them as functions of Pierce's TWT parameters. A conclusion is that the electronic reflexions often exceed the cold reflexions that can be obtained in practice. The electronic reflexions in TWT's with a backward fundamental coupled-cavity structure are almost an order of magnitude larger than those in helix TWT's.     

A two wave theory of traveling-wave tubes and backward-wave oscillations

Starting from Pierce's small-signal TWT equations, a two-wave theory for complicated TWT's and BWO's is developed. Explicit gain expressions for TWT's with severs and velocity tapers are given. A detailed treatment is given of a BWA structure with a single-step velocity taper in the center. The BWO start oscillation current is calculated as a function of the taper strength. The effciency of a step velocity taper as a remedy for backward-wave oscillations in the higher passbands of a TWT is then analyzed. It is shown that a suitable taper can increase the start oscillation current by more than a factor of 10 without adverse effects on the TWT performance if the backward waye coupling impedance is low. A tube with a weak linear taper is analyzed by a perturbation technique and it is found that there is no significant difference between the start oscillation currents for tubes with weak linear or abrupt tapers of comparable strengths.     

TWT Equal Carrier Intermodulation Calculations

When more than one FM carrier is put through a TWT (or SSPA), the output consists of the original carriers plus intermod lines. The procedure for calculating these lines has been studied by several authors in recent years because of the rapid growth of satellite communications in which TWT's (and SSPA's) play a major role. Basically, these intermod calculations are used to design multiple carrier arrangements in a single satellite transponder so that the transponder can be filled to its capacity. Since this optimum point is usually achieved when the carriers are unequal in power, the methods derived so far have focused on this case. However, if an equal carrier case must be evaluated just once, and the number of carriers is moderately high and the intermod order is high (greater than third order), the present known methods are unsuitable. This report will present a method for solving this special case.     

行波管关断方式对应用系统可靠性的影响

行波管在工作一段时间以后其电子枪各极间绝缘电阻可能发生变化,因此针对行波管的特点,设计出可靠的工作电源及行波管关断电路是保证武器装备可靠性的重要因素之一。在行波管电子枪极间绝缘电阻变小时,某应用系统行波管关断电路因不能使行波管完全关断,造成管体温度上升,保护电路动作,从而导致出现了雷达发射机无法及时开启的故障。文中通过对2种行波管关断方式等效电路的讨论,提出了避免应用系统故障的有效关断电路模式。     

用ANSYS软件对行波管收集极进行辐射热分析

着重介绍了ANSYS有限元分析软件在行波管收集极辐射热分析方面的工作，辐射热分析的结论可以为实际中收集极的设计工作提供一些参考和依据。     

High-power linear-beam tubes

High-power klystrons, coupled-cavity traveling-wave tubes (TWT's), and hybrid tubes, all of which utilize the microwave cavity as the basic circuit element, are described. These amplifiers are used in communications, radars, electronic countermeasures, and other applications at power levels from a few hundred watts to megawatts, at frequencies from ultrahigh frequency on up, and are particularly suited for high average powers. High gain, 30 to 60 dB, is normally achieved, and bandwidth usually lies in the 1-30-percent range. Elementary theory of operation is described, together with design considerations and systems interface information. Typical tube designs and data are presented. Recent developments are discussed, including high-efficiency techniques (to 75 percent), improvements in bandwidth, periodic focusing, and beam control electrodes. Most of the basic design techniques are well developed, and emphasis is being shifted to improvements in the detailed performance characteristics such as gain and phase resolution ripples, noise, and the sensitivities to operating voltages and currents.     

周期永磁聚焦系统直流状态下聚焦性能的计算机模拟

本文概略地阐述了作者研制的行波管周期永磁聚焦系统ＣＡＤ软件的原理，计算方法和功能，该软件包含有计算程序和前，后图形处理程序，计算程序的精确满足工程设计要求，是行波管周期永磁聚焦系统的良好辅助设计手段。     

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.     

The effect of helix loss on noise figure in traveling-wave tubes

Helix loss increases the noise figure of a TWT by altering the amplifying properties of the tube, and also by acting as a source of thermal noise which is amplified by interaction with the beam. Noise power originating in the helix propagates as a wave and undergoes amplification in the same manner as the signal. This noise power adds to the noise figure of the tube by an amount proportional to the attenuation of the helix and to its temperature, and inversely proportional to the tube gain per unit length. The effect of refrigerating the helix has been demonstrated by several experiments in which low-noise TWT's were immersed in liquid nitrogen while monitoring the noise figure. The reduction in noise figure varied from a few tenths to nearly one db. One case of particular interest is that of a WJ-226 low-noise TWT, operating in the frequency band 1.4 to 2.3 Gc, which showed a minimum noise figure of 2.6 db when operating in a room temperature environment. On cooling the tube to liquid nitrogen temperature, a minimum noise figure of 1.7 db was obtained, at a frequency of 1.65 Gc.     

人工智能(AI)在电力系统中的应用

简要地介绍了人工智能技术的基本概念,并指出其在电力系统中的应用范围。对专家系统、人工神经网络、模糊理论、遗传算法等人工智能技术的基本概念进行了简单的介绍,并从实用化的观点对他们在电力系统故障诊断中的应用特点、存在问题进行分析,最后指出综合运用多种人工智能技术是电力系统中的人工智能技术应用的最新发展动向,并提出了有针对性的建议。