Comparative research on three types of coaxial slow wave structures

This paper studies three types of coaxial slow wave structures （SWSs）： （1） with ripples on both the inner and outer conductors; （2） with ripples on the outer conductor and smooth on the inner one; and （3） with ripples on the inner conductor and smooth on the outer one. The frequencies, coupling impedances, time growth rates and beam-wave interaction efficiencies of the three types of coaxial SWSs are obtained by theoretical analysis. Moreover, the relativistic Ccrenkov generators （RCGs） with the three types of coaxial SWSs are simulated with a fully electromagnetic particle- in-cell code, and the results verify the theoretical analysis. It is proved that the RCG with double-rippled coaxial SWS has the highest conversion efficiency and the shortest starting time.

Variational analysis of the disc-loaded waveguide slow-wave structures

The variational method is applied to calculate the dispersion characteristics of disc-loaded waveguide slow-wave structures. The parameters describing the waveguide discontinuities in disc-loaded waveguide are calculated by the variational method. Then the dispersion characteristics of slow-wave structures are obtained using lossless microwave quadrupole theory. Good agreement was observed between results of the Variational method and those of field matching method and high frequency structure simulator. In the case of broad band, results of the variational method are better than those of field matching method.

A novel slotted helix slow-wave structure for high power Ka-band traveling-wave tubes

A novel slotted helix slow-wave structure （SWS） is proposed to develop a high power, wide-bandwidth, and high reliability millimeter-wave traveling-wave tube （TWT）. This novel structure, which has higher heat capacity than a conven- tional helix SWS, evolves from conventional helix SWS with three parallel rows of rectangular slots made in the outside of the helix tape. In this paper, the electromagnetic characteristics and the beam-wave interaction of this novel structure operating in the Ka-band are investigated. From our calculations, when the designed beam voltage and beam current are set to be 18.45 kV and 0.2 A, respectively, this novel circuit can produce over 700-W average output power in a frequency range from 27.5 GHz to 32.5 GHz, and the corresponding conversion efficiency values vary from 19% to 21.3%, and the maximum output power is 787 W at 30 GHz.

Research of sine waveguide slow-wave structure for a 220-GHz backward wave oscillator

A watt-class backward wave oscillator is proposed, using the concise sine waveguide slow-wave structure combined with a pencil electron beam to operate at 220 GHz. Firstly, the dispersion curve of the sine waveguide is calculated, then, the oscillation frequency and operating voltage of the device are predicted and the circuit transmission loss is calculated. Finally, the particle-in-cell simulation method is used to forecast its radiation performance. The results show that this novel backward wave oscillator can produce over 1-W continuous wave power output in a frequency range from 210 GHz to 230 GHz. Therefore, it will be considered as a very promising high-power millimeter-wave to terahertz-wave radiation source.

A novel multi-pin rectangular waveguide slow-wave structure based backward wave amplifier at 340 GHz

A backward wave amplifier（BWA） in a terahertz regime with a novel slow-wave structure（SWS） composed of multi parallel grating pins inside a rectangular waveguide is analyzed. The multi-pin rectangular waveguide SWS possesses good performance and is compatible with micro-fabrication technologies. The dispersion and interaction impedance of the multipin SWS are presented. The stopbands of the modes cling together in a Brillouim zone. The SWS has a high interaction impedance that is suitable for the interaction of multi cylindrical beams. The design, which is based on three parallel pins supporting the wave–beam interaction with four cylindrical beams, is verified by three-dimensional particle-in-cell simulations. A BWA with the central frequency at 340 GHz is demonstrated, and the output power is more than 100 mW.A tuning frequency range of 15 GHz（333–348 GHz） is obtained with a gain of more than 20 dB.

Dispersion characteristics of a slow wave structure with a modified photonic band gap

This paper studies the dispersion characteristics of a modified photonic band-gap slow-wave structure with an open boundary by simulation and experiment. A mode launcher with a wheel radiator and a coupling probe is presented to excite a pure TM01-like mode. The cold test and simulation results show that the TM01-like mode is effectively excited and no parasitic modes appear. The dispersion characteristics obtained from the cold test are in good agreement with the calculated results.

THE COUPLING IMPEDANCE OF VANE-LOADED TAPE HELIX SLOW-WAVE STRUCTURE

Based on the actual vane-loaded tape helix slow wave structure, a new theoretical analytic model for calculating coupling impedance is proposed by Chen Qingyou, et al.(1999)with calculated values of dispersion in good agreement with measured ones. In this paper, it is continued to use this model to calculate the coupling impedance of such a structure, and analyze the effects of the propagation power within vane gaps and the helix gap on the coupling impedance.As a result, the theoretical values are found to be in good agreement with the measured ones,with the maximum difference less than ±18%.

A Comparative Study of Dispersion Characteristics Determination of a Trapezoidally Corrugated Slow Wave Structure Using Different Techniques

The linear dispersion relation of a trapezoidally corrugated slow wave structure （TCSWS） is analyzed and presented. The size parameters of the TCSWS are chosen in such a way that they operate in the x-band frequency range. The dispersion relation is solved by utilizing the Rayleigh-Fourier method by expressing the radial function in terms of the Fourier series. A highly accurate synthetic technique is also applied to determine the complete dispersion characteristics from experimentally measured resonances （cold test）. Periodic structures resonate at specific frequencies when the terminals are shorted numerical calculation, synthetic technique and cold appropriately. The dispersion characteristics obtained from test are compared, and an excellent agreement is achieved.

Three-dimensional simulation of a Ka-band relativistic Cherenkov source with metal photonic-band-gap structures

This paper presents a three-dimensional particle-in-cell （PIC） simulation of a Ka-band relativistic Cherenkov source with a slow wave structure （SWS） consisting of metal photonic band gap （PBG） structures. In the simulation, a perfect match layer boundary is employed to absorb passing band modes supported by the PBG lattice with an artificial metal boundary. The simulated axial field distributions in the cross section and surface of the SWS demonstrate that the device operates in the vicinity of the π point of a TM01-1ike mode. The Fourier transformation spectra of the axial fields as functions of time and space show that only a single frequency appears at 36.27 GHz, which is in good agreement with that of the intersection of the dispersion curve with the slow space charge wave generated on the beam. The simulation results demonstrate that the SWS has good mode selectivity.

Investigation of a wideband folded double-ridged waveguide slow-wave system

The folded double-ridged waveguide structure is presented and its properties used for wide-band traveling-wave tube are investigated. Expressions of dispersion characteristics, normalized phase velocity and interaction impedance of this structure are derived and numerically calculated. The calculated results using our theory agree well with those obtained by using the 3D electromagnetic simulation software HFSS. Influences of the ridge-loaded area and broad-wall dimensions on the high frequency characteristics of the novel slow-wave structure are discussed. It is shown that the folded double-ridged waveguide structure has a much wider relative passband than the folded waveguide slow-wave structure and a relative passband of 67% could be obtained, indicating that this structure can operate in broad-band frequency ranges of beam-wave interaction. The small signal gain property is investigated for ensuring the improvement of bandwidth. Meanwhile, with comparable dispersion characteristics, the transverse section dimension of this novel structure is much smaller than that of conventional one, which indicates an available way to reduce the weight of traveling-wave tube.

Small-signal analysis of a rectangular helix structure traveling-wave-tube

This paper investigates the properties of traveling wave-beam interaction in a rectangular helix traveling-wave-tube （TWT） for a solid sheet electron beam. The ＂hot＂ dispersion equation is obtained by means of the self-consistent field theory. The small signal analysis,which includes the effects of the beam parameters and slow-wave structure （SWS） parameters,is carried out by theoretical computation. The numerical results show that the bandwidth and the small-signal gain of the rectangular helix TWT increase as the beam current increases;and the beam voltage not obviously influences the small signal gain. Among different rectangular helix structures,the small-signal gain increases as the width of the rectangular helix SWS increases,however,the bandwidth decreases whether structure parameters a and L or ψ and L are fixed or not.In addition,a comparison of the small-signal gain of this structure with a conventional round helix is made.The presented analysis will be useful for the design of the TWT with a rectangular helix circuit.

Frequency Tunability and Slow-Wave Characteristics of a High-Efficiency Ridged MILO

A high-efficiency ridged magnetically insulated transmission line oscillator (RMILO) is proposed and investigated theoretically and numerically in this paper. In the RMILO, ridge-disk vanes are introduced to enhance the power efficiency. Theoretical investigation shows that the ridge-disk can enhance the coupling impedance of the slow-wave structure (SWS), and so enhance the power efficiency. Moreover, the ridge has a weak influence on frequency, so, it influences little on the tunability of the MILO. In simulation, when the applied voltage is increased to 807 kV, the RMILO can get the 3 dB tunable frequency range with 7.6 - 13.9 GHz and the 3 dB tuning bandwidth with 58.6% which has an increase of 27.6% compared with the conventional MILO. So, the tuning performance of the RMILO is more superior. Besides, the RMILO gets the maximum output power of 7.1 GW, the corresponding power efficiency is 22.6% and the frequency is 1.400 GHz. Furthermore, when the applied voltage is increased to 807 kV, high-power microwave with a power of 13.5 GW, frequency of 1.400 GHz, and ef?ciency of 24.5% is generated, which has an increase of 20.2% compared with the conventional MILO. The simulation results con?rm the ones predicted by theoretical analysis.

耳型折叠波导慢波结构W波段行波管

毫米波行波管具有大功率、宽频带、高增益等特点,广泛用于雷达、高速通信、电子对抗等现代军事装备中。为提高折叠波导耦合阻抗并考虑工程应用性,提出一种耳型折叠波导新型慢波结构。与常规矩形波导相比,工作频带内耦合阻抗提高30%以上,损耗降低10%。研制的耳型折叠波导W波段行波管,在工作电压21.9 kV,电流210 mA,占空比为5%时,10.8 GHz带宽内输出功率大于192 W,峰值功率达278 W,电子效率和增益分别达到6.3%和44.6 dB,行波管工作稳定。

一种束半径可调的环形强流电子束产生技术及应用

束半径可调的强流环形电子束在跨波段跳频高功率微波产生器件中有重要应用。提出了一种改变外加引导磁场位形从而改变环形强流电子束半径的技术。该技术的核心部件由环形阴极、阳极、电子束转移通道、电子束传输通道和三段螺线管组成。当三段螺线管的通流的电流大小不一样时,该螺线管系统就能产生不同位形的磁场。在粒子模拟中,当三段螺线管的通流电流大小分别为1025 A、107 A、107 A和300 A、300 A、0 A时,螺线管产生两种不同位形的磁场,实现电子束半径的改变。从单粒子运动理论出发,本文推导出电子束在梯度磁场引导下的运动轨迹表达式,解释了电子束半径在梯度磁场下变化的原理,还研究了梯度磁场的斜率和极差对电子束轨迹的影响。在跨波段器件仿真中,X波段输出功率为1.6 GW,频率为8.2 GHz,效率为40%;Ku波段输出功率为1.5 GW,频率为14.4 GHz,效率为38%。

基于T形四周期谐振慢波结构的X波段高功率微波产生技术的理论与仿真

优化设计了T形四周期谐振慢波结构,并进行了高频理论分析.利用镜像法将T形波导单元进行脊波导化等效设计,并通过等效电路分析了等效脊波导的高频特性,由此进行T形波导的谐振频率与结构解析理论分析.在此基础上构造了T形四周期谐振慢波结构,对该结构进行色散特性分析,确定谐振模式和频率,得到了模式同步电压范围.最后基于提出的T形周期谐振慢波结构进行对应的相对论扩展互作用辐射源的仿真验证.通过三维粒子仿真模拟分析及优化设计,在448 kV注电压、400 A注电流和0.4 T的均匀轴向磁场条件下,得到了频率为9.8 GHz、平均输出功率71.4 MW的高功率微波,对应电子效率为39.8%.本文提出的以T形波导为单元的新型谐振慢波结构有效地利用较少周期实现高效率、高功率微波产生,为高功率微波科学提供了有效的高频结构的紧凑化方案.

基于新型超宽带慢波微带传输线的设计

效率高、体积小、质量轻的微波无源器件是5G频段移动通信覆盖的必备设备。文中在研究传统微带型曲折线慢波结构和开路枝节加载基础上,提出基于超宽带慢波微带传输线的设计并进行研究,利用电磁场仿真软件HFSS对该慢波微带传输线进行模拟仿真,仿真结果表明,超宽带慢波结构与普通微带线相比,频带宽,尺寸小,损耗低,成本低,满足5G通信系统的需求。最后通过对加载了所提出的新型慢波微带传输线的小型化U型移相器的实验数据分析表明,该新型慢波微带传输线在基站天线系统中有着广阔的市场应用前景。

W波段平面集成行波管高频系统设计及验证

针对W波段平面一维阵列集成行波管设计,采用非半圆弯曲变形折叠波导慢波结构和聚焦极调制皮尔斯电子枪,基于CST、MTSS和Opera软件优化设计了集成行波管高频系统和电子光学系统,实现了W波段低电压小电流工作的低功率行波管设计,通过周期永磁(PPM)聚焦系统制管验证了高频系统和电子枪设计的合理性。测试结果表明,行波管在工作电压12.62 kV,工作电流31.6 mA条件下,输出功率大于10 W的带宽达到5 GHz,增益优于28 dB,总效率优于10%,测试结果与设计结果具有较好一致性,为W波段行波管实现阵列集成提供技术支撑。

A staggered double vane circuit for a W-band traveling-wave tube amplifier

Based on the combination of a staggered double vane slow wave structure （SWS） and round electron beam, a 200-W W-band traveling-wave tube （TWT） amplifier is studied in this paper. The main advantages of round beam operation over the sheet beam is that the round beam can be formed more easily and the focus requirement can be dramatically reduced. It operates in the fundamental mode at the first spatial harmonic. The geometric parameters are optimized and a transition structure for the slow wave circuit is designed which can well match the signal that enters into and goes out from the tube. Then a TWT model is established and the particle-in-cell （PIC） simulation results show that the tube can provide over 200-W output power in a frequency range of 88 GHz-103 GHz with a maximum power of 289 W at 95 GHz, on the assumption that the input power is 0.1 W and the beam power is 5.155 kW. The corresponding conversion efficiency and gain at 95 GHz are expected to be 5.6% and 34.6 dB, respectively. Such amplifiers can potentially be used in high power microwave-power-modules （MPM） and for other portable applications.

Linear theory of beam–wave interaction in double-slot coupled cavity travelling wave tube

A three-dimensional model of the double-slot coupled cavity slow-wave structure （CCSWS） with a solid round elec- tron beam for the beam-wave interaction is presented. Based on the ＂cold＂ dispersion, the ＂hot＂ dispersion equation is derived with the Maxwell equations by using the variable separation method and the field-matching method. Through numerical calculations, the effects of the electron beam parameters and the staggered angle between adjacent walls on the linear gain are analyzed.