Dynamic defocusing of electron beams in high-power helical traveling-wave tubes with length-dependent dispersion

Dynamic defocusing in a wideband helical traveling-wave tube (TWT) with an output power of 1.5–2.0 kW in the continuous-operation mode is analyzed. The TWT contains fragments with normal and anomalous dispersion of the phase velocity. It is demonstrated that the TWT output characteristics can be improved and the TWT stability against self-excitation on the backward wave can be increased with the use of appropriate values of parameters of the electron-optical system that forms a converging axially symmetric beam focused by a periodic permanent-magnet focusing system.     

Analysis of the methods to increase the output power and frequency of the broadband TWTs

The limitations on the output power and operating frequency of the broadband TWTs resulting from a relatively low thermal stability of helix and the self-excitation at the backward wave at a operating voltage of greater than 10 kV are considered. The analysis yields the methods to overcome limitations: the application of a bifilar helix with the azimuthally conducting rings and the application of combined metal-dielectric supports that allow a simultaneous improvement of the heat removal from the helix and an increase in the TWT band. It is demonstrated that a decrease in the slowing caused by the rings and a smaller period of the bifilar helix make it possible to shift the threshold of the self-excitation at the backward wave to 30–40 kV.     

Suppression of self-excitation of a backward-wave traveling-wave tube by decreasing the diameter and the pitch of the slow-wave structure toward the energy output

Mathematical expressions showing that the optimum way of suppressing the self-excitation of a backward-wave traveling-wave tube is to decrease the diameter and pitch of the slow-wave structure toward the energy output are obtained. The conditions for the values of the diameter and pitch before and after the decrease are found under which the phase velocities of the minus first spatial harmonic (backward wave) are maximally different, which ensures the maximum suppression of self-excitation, and phase velocities of the zero harmonic are optimal for obtaining the maximum efficiency.     

Design of a tapered helix for suppressing backward wave oscillations in MMW TWT’s

Backward wave oscillations are easy occurred in high power helix millimeter wave traveling wave tubes (MMW TWT’s), owing to larger ka value and higher operating voltage. The start current of backward wave is calculated for helix TWT in Ka band. It is shown that start current will increase by used a tapered helix. Backward wave oscillations can be suppressed in tube. The design method of the tapered helix is given in this paper.     

A Fast Computation of the Start-Oscillation Current of Backward Wave in MMW HTWT's

Backward wave oscillation can be troublesome in high power helix TWT, especially millimeter wave helix traveling wave tubes (MMW HTWT's). To suppress these oscillations, start-oscillation current of backward wave has to know when MMW HTWT's are designed. A fast computation of the start-oscillation current for MMW HTWT's is presented. It is shown that the computed values are agreed with the experimental results in Ka band.     

Calculation of the Parameters for Ring-loop Traveling Wave Tube in MMW

The feature of the ring-loop slow wave structure is high coupling impedance and low harmonic wave components. Therefore ring-loop traveling wave tube (TWT) has advantages of high gain, small dimension, higher operating voltage and less danger of the backward wave oscillation. But calculation of the ring-loop is rather difficult. Here on basis of calculation of dispersion and impedance, a fast estimation of interaction efficiency, output power and saturated gain for Ka-band ring-loop TWT are given.     

Design and fabrication of a sub-millimeter multi-beam folded waveguide structure

A novel multi-beam folded waveguide (MBFW) circuit, which can enhance the output power and interaction efficiency of sub-terahertz (THz) traveling wave tube (TWT), is presented in the paper. Operating with fundamental mode and multiple electron beams means that a larger beam current can be used for a higher output power. The characteristics of the MBFW structure are analyzed and optimized. Compared with the single-beam folded waveguide (SBFW) TWT, the output power of the MBFW TWT increases from 3.64 W to 25.45 W at 140 GHz and its electronic efficiency increases from 1.06% to 7.4% under the conditions of an input peak power of 10 mW, a beam voltage of 9.55 kV and a current of 12 mA. The optimized MBFW structure can be successfully fabricated by micro milling, with dimension errors below expectation, and the measured transmission characteristics are in good agreement with the design.     

Study of Propagating Characteristics for Folded Waveguide TWT in Millimeter Wave

Folded waveguide circuit (FWC) is an ideal slow wave structure for broadband power traveling wave tube (TWT) in millimeter wave. But owing to changes of propagating character by reflecting of waveguide bend and electron beam hole, stopband can be formed. On the basis of computation of the stopband, effects of the dimension of FWC on stopband width are analyzed. It is available for design in FWC TWT.     

多注行波管慢波结构的色散特性分析

多注行波管是一种具有工作电压低、瞬时工作带宽宽、容易实现大功率等优点的新型微波器件;本文主要利用CST Microwave Studio软件对多注行波管慢波结构的色散特性进行设计计算,并将计算结果和实验值进行比较分析。结果表明,计算值和实验值基本吻合。     

倍频程螺旋线行波管2.5维大信号分析和设计

本文利用2.5维大信号分析程序和辅助分析程序,对一只7-18GHz带宽,2-2.5kW脉冲输出功率的螺旋线行波管进行计算机模拟,电子注感应电流基波分量在螺旋线慢波系统高频场中的相位分析和最佳工作点分析。在此基础上,探讨了色散曲线布局,衰减器配置,切断位置,再同步设计等倍频程螺旋线行波管的设计方法。     

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.     

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.     

E波段连续波空间行波管研制进展

针对高波段空间行波管的卫星通信应用需求,介绍了E波段连续波空间行波管的研制情况。该行波管通过进一步优化折叠波导慢波结构参数和调整周期跳变方案,实现改善带内增益波动性、提高效率的目的。研制出的样管在14.7 kV、74 mA条件下,实现电子注动态流通率高于98%,在71~76 GHz范围内,输出功率大于85 W,总效率大于37%,增益大于40 dB。     

多注太赫兹折叠波导行波管的设计与模拟

为解决太赫兹(THz)行波管工作电流过小、输出功率低等问题,提出了基模多注工作模式的折叠波导行波管(TWT)。首先,获得了基模多注折叠波导色散特性;然后,对基模多注折叠波导的传输特性进行了模拟计算;最后,完成了0.14 THz基模多注折叠波导行波管的注波互作用特性分析。电子注参数为12 m A,15.75 k V时,获得的3 d B带宽为25 GHz(128 GHz~153 GHz),最大增益为33.61 d B,最大峰值功率为23 W;电子注参数为30 m A,15.75 k V时,在0.14 THz处获得了38 d B增益,最大脉冲输出功率为63.1 W。该方法能够有效增大THz行波管的工作电流,提高互作用增益及效率、3 d B带宽、输出功率;在增益相同时,基模多注行波管可以做得更短、更紧凑。     

Design of Coupling Structure for MMW Folded Waveguide TWTs

A significant advantage of the folded wave traveling wave tube (TWT) is simple coupling structure. In millimeter wave band, owing to higher frequency, linear double taper can be used as impedance transformer. The design method and calculation results for the folded waveguide TWTs in Kα-band are given.     

X波段大功率螺旋线型脉冲行波管的研制

介绍了两种螺旋线型脉冲行波管,通过抑制返波振荡和提高螺旋线散热能力,在X波段获得了8 kW峰值功率和400 W平均功率。同时进行了初步的功率合成试验,并取得了较好的结果。     

Performance study of 16-ary deqam modem for future satellite communication systems

This paper investigates the effects of additive white Gaussian noise (AWGN), adjacent-channel interference (ACI) and co-channel interference (CCI) combined with flat fading on the performance of bandlimited 16-ary differentially encoded quadrature amplitude modulation (16-ary DEQAM) signalling transmitted through a non-linear high-power amplifier (HPA). It is assumed that the HPA exhibits both AM-AM and AM–PM conversion distortions. This situation may be applied to the up-link or down-link of a regenerative satellite system where the HPA is the earth-station travelling-wave tube (TWT) or the on-board TWTA, respectively. The signal-to-noise ratio (SNR) degradations at a specific bit error rate (BER) are evaluated by means of a series of computer simulation tests for various values of channel roll-off factor α (channel bandwidth) and different degrees of output backoff (OBO) of the HPA in the presence of various combinations of the channel impairments. It is shown that by employing a baseband or RF predistortion technique for the HPA and selecting the best arrangement of channel roll-off factor, OBO value of the HPA and channel spacing, a good performance can be achieved regarding the most efficient use of bandwidth together with a minimum SNR degradation due to the presence of channel impairments. Thus, the use of 16-ary DEQAM for satellite communications is feasible in the near future.     

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.     

Influence of variations in the phase velocity and coupling impedance under the absorbing layer on the output characteristics of a wideband traveling-wave tube

The electrodynamic parameters (coupling impedance, slowing factor, and damping factor) of a wideband traveling-wave tube (TWT) are calculated as functions of the surface resistance of the absorbing layer and of the frequency. The data obtained are approximated by quadratic polynomials within a wide range of values of the parameters, and a PC program is developed for computing the coupling impedance and slowing factor in the absorbing layer as functions of the longitudinal distribution of the damping factor and of frequency. The effect of these dependences on the output and statistical characteristics of a wideband TWT is analyzed. It is shown that the maximum effect is produced at the long-wavelength edge of the operating frequency range.     

通信行波管转移特性测试方法

行波管一般作为微波放大器的末级,其性能好坏直接影响到通信整机系统的性能。在测试过程中,由于受到矢量网络分析仪的信号源输出功率和行波管增益限制,多采用固态放大器作为前级放大器推动行波管达到所需功率要求,因此不能直接精确得到行波管自身的特性。采用本测试方法可以去除固态放大器的影响,提高测试行波管的转移特性曲线的准确度。