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。     

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％.     

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.     

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.     

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.     

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.     

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     

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.     

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     

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.     

电源纹波对常规相参雷达改善因子的影响

分析电源纹波对TWT级联发射机放大链引起非线性失真的原因,通过对非非线性失真公式进行变换,导出发射电源纹波与相参雷达MTI改善因子的关系式,给出衡量电源纹波的参数,为雷达系统设计选择TWT和确定电源纹波参数指标提供了定量理论依据。     

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.     

发射机非线性放大失真对脉压雷达改善因子的限制

分析了电源纹波对行波管（ＴＷＴ）级联发射机放大链引起非线性失真对线性调频脉冲压缩雷达的影响,通过对非线性失真公式进行变换,导出了发射电源纹波与线性调频脉压雷达ＭＴＩ改善因子的关系式,为雷达系统设计选择ＴＷＴ和确定电源纹波参数指标提供了定量理论依据。     

Frequency-Independent and Frequency-Dependent Nonlinear Models of TWT Amplifiers

Simple two-parameter formulas are presented for the functions involved in the amplitude-phase and the quadrature nonlinear models of a TWT amplifier, and are shown to fit measured data very well. Also, a closed-form expression is derived for the output signal of a TWT amplifier excited by two phase-modulated carriers, and an expression containing a single integral is given when more than two such earriers are involved. Finally, a frequencydependent quadrature model is proposed whose parameters are obtainable from single-tone measurements.     

Use of auger spectroscopy in the evaluation of thermionic cathodes

The ability of Auger spectroscopy to identify chemical species existing on a surface has been used to evaluate the properties of "good" and "poor" impregnated tungsten cathodes used in high-power microwave wave tubes. The surfaces of "good" and "poor" cathodes were studied by means of Auger spectroscopy and work function measurements and the results interpreted to analyze failure modes in cathodes removed from TWT's because of poor emission characteristics. Most of the poor cathodes evaluated in this program were obtained from fabricated electron guns that had been employed and discarded from the 200-W TWT tubes developed for the Communication Technology Satellite (CTS) program. The results of these measurements have shown there are at least two types of failure modes that one observes with poor cathodes. They are 1) chemical contamination of the cathode surface and 2) low partial layer barium coverage of the cathode surface.     

Spacecraft Technology for Broadcasting Satellites--An Update

This paper surveys the special technologies for presently conceived direct broadcast satellite (DBS) projects using high RF power in the band 12.2-12.7 GHz, allocated to the broadcasting-satellite service in the western hemisphere. The technologies include launch vehicles, shapedbeam antennas, traveling wave tubes (TWT's), electronic power conditioners (EPC's) for TWT's, lightweight high-power solar arrays, heat-pipe radiators, and output multiplexers. It is concluded that the technology is available, and only detailed engineering development and testing is required for construction.     

Study on Ka-Band Sheet Beam Traveling Wave Tube Focused by Closed PCM

This paper reports a Ka-band sheet beam traveling wave tube (TWT) focused by a 0.2 T closed periodic cusped magnet (PCM) system. The TWT with one section of staggered double-vane slow-wave structure (SWS) is driven by a 0.8-A sheet beam with rectangular cross-sectional area of 3.2 mm?×?0.6 mm. This sheet beam TWT can produce 100 W output power, and the 3 dB band is 33–38.5 GHz. In order to improve the output power, an optimized sheet beam TWT with two sections of SWSs focused by a novel closed PCM system is proposed. The new closed PCM system is with annular magnetic blocks and can be fabricated and adjusted easily. The simulation shows that the optimized sheet beam TWT can produce 2000 W output power and the 3 dB band ranging from 33 to 40 GHz.     

A theoretical description for the multiple-signal operation of a TWT

A multiple-large-signal theory for traveling-wave tubes (TWT's) is developed. The equations associated with the growth of the signal waves along the length of the tube are integrated by means of digital computation methods. The assumptions made during the theoretical formulation are more restrictive than those made by El-Shandwily in his multiple-large-signal theory, however, by restricting the generality of the theory judiciously, the computer time normally required to make calculations of this type is substantially reduced, Calculations have been presented for only a few special cases. Computed results are presented here for the growth of up to 12 input signals and some of the more imporant intermodulation products. Agreement between theoretical predictions and experimental results are shown for the case of two input signals. In addition some important empirical relations are developed which can be used to approximately predict the large signal performance of a TWT and to further reduce the computer time.     

Improvement of the output power in TWTs by harmonic injection

The possibility of improving the fundamental output power of a traveling wave tube (TWT) using second harmonic injection is presented in this paper with theoretical, numerical, and experimental approaches. A calculus of the energy extracted from an electron beam subjected to a bi-harmonic field is presented in the low-gain regime, and it shows how the shape of the field can increase the fundamental extracted power. The phase difference between the fundamental and harmonic waves appears to be a key parameter for harmonic injection. The large signal code TUBH from Thales Electron Devices is used to simulate a TWT where both the fundamental and harmonic waves travel with the same velocity and the same growth rate. Harmonic injection simulations show that the fundamental output power is optimized when the total energy extracted from the beam is maximized, and the fundamental wave is favored to the detriment of the harmonic wave. A three-dimensional version of the code, called MVTRAD, is used to simulate an industrial TWT manufactured at Thales. Experimental measurements on this TWT completed this paper, showing a significant increase of fundamental output power with harmonic injection with up to 86% of additional power at 5 GHz.     

遗传算法在螺旋线行波管优化中的应用

遗传算法是一种可以对包含多个连续变量的目标函数进行全局优化的算法。本文在一维频域理论互作用程序的基础上,采用遗传算法对螺旋线行波管的慢波结构进行了全局优化设计,提高了行波管的互作用效率。在单频点优化过程中,螺旋线分成三段的情况下,利用遗传算法优化了输出功率最大的最佳螺旋线长度,然后利用遗传算法对多段螺旋线问题进行了优化。为了满足带宽的要求,本文又利用高低端优化的方法对螺旋线行波管进行了带宽优化,得出了一组高效的满足带宽条件的螺旋线行波管慢波结构的制管参数。