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.

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.

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 method of designing photonic crystal grating slow-wave circuit for Ribbon-Beam microwave travelling wave amplifiers

A method of designing a photonic crystal grating slow-wave circuit in which the cylinders of the 2D photonic crystals dot on a cross-sectional plane is established by calculating the band structures of the 2D photonic crystals, and the eigenfrequency of the equivalent waveguide grating. For calculating the band structures, the eigenvalue equations of the photonic crystals in the system of photonie crystal grating slow-wave circuit are derived in a special polarization mode. Two examples are taken to show the method. The design result is validated by the scattering parameters of the same circuit. The result indicates that there exists no photonic band gap if the metal gratings do not extend into the photonic crystals; the design of the circuit without the metal gratings extending into the photonie crystals is less flexible than that with the metal gratings extending into the photonic crystals.

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.

Automated Synthesis of Wideband Bandpass Filters Based on Slow-Wave EBG Structures

This paper is focused on the automated synthesis of wideband bandpass filters operating at microwave frequencies and based on electromagnetic bandgap(EBG)structures.The classical counterpart of such filter consists of a combination of transmission line sections and shunt-connected grounded stubs placed at equidistant positions.By replacing the transmission line sections with capacitively-loaded lines(a kind of EBG-based lines)exhibiting the same phase shift at the lower cutoff frequency and the same characteristic(actually Bloch)impedance,filter size is reduced and the spurious pass bands can be efficiently suppressed.In practice,the loading capacitances are implemented by means of patches,in order to achieve a fully planar filter implementation.The presence of the patches reduces the effective phase velocity of the capacitively-loaded lines,thus providing a slow-wave effect useful for filter miniaturization.Moreover,due to periodicity,such EBG-based lines exhibit wide stop bands,which are used for spurious suppression.Even though such EBGbased filters were previously reported by some of the authors,a systematic synthesis method was not applied for filter design.In this paper,the main aim is to demonstrate the potential of aggressive space mapping(ASM)for that purpose,and it will be shown that such filters can be automatically synthesized.

A Metamaterial Design Based on Electromagnetic Induction Transparency-Like Effect and Its Slow-Wave Performance

This paper proposes a new metamaterial design that can achieve electromagnetic induction transparency-like (EIT-like) effects in the microwave band. The unit structure of metamaterials consists of square rings and metal wires. The square ring acts as the “bright state” and the metal wire acts as the “dark state”. The destructive interference between the bright state and the dark state produces an EIT-like effect. In the simulation results, a transparent window centered at 4.00 GHz can be observed in the transmission spectrum. By studying the phase change of the transparent window, it is found that the group delay of the metamaterial structure can reach 0.39 ns at 4.00 GHz. This paper also studies the influence of the refractive index of the medium on the EIT-like effect. Numerical simulations show that such metamaterial is very sensitive to the refractive index of the medium, and the sensitivity is 15 mm/RIU. Our design can be extended to other frequency bands and may have potential applications in filtering, sensing, slow-light devices, and nonlinear optics.

1.03THz折叠波导慢波结构及电子光学系统研究

太赫兹真空电子器件成为未来主要的发展方向,本文对1.03 THz折叠波导慢波结构及电子光学系统进行了研究,分析了不同电子注通道形状对于折叠波导特性的影响,包括色散特性、耦合阻抗、衰减特性、功率、增益等,并且利用OPERA 3D软件设计了电子光学系统。仿真结果表明,在中心1.03 THz频率处,与矩形电子注通道折叠波导慢波结构相比,圆形电子注通道的结构色散曲线更为平缓,耦合阻抗提升6.9%,损耗降低6.8%;在10 GHz带宽内功率提升47.4%,增益提升1.2 dB,互作用长度缩短12.3%。在工作电压为17.4 kV时,阴极发射电流大于3 mA,电子注半径为0.012 mm,在均匀区永磁聚焦系统中可稳定传输。

矩形栅慢波系统的高频特性分析

对于矩形栅这一经典的慢波结构,采用场匹配法来分析其慢波特性,进而得到其耦合阻抗。其中对槽区内的场处理,保留其高次项,表示为一无限本征驻波之和的形式。然后通过数值实例具体分析了矩形栅的两种典型结构:浅槽栅和深槽栅。当增大槽深后,色散增强,系统通带变窄,同时耦合阻抗有明显增大,工作点移向前向波区,适合用在放大器的慢波结构上。

曲折圆形槽波导慢波系统的高频特性

对曲折圆形槽波导新型慢波系统的高频特性进行了研究,通过理论分析和数值计算,得到了它的色散曲线和耦合阻抗表达式,并分析了结构参数变化对色散特性和耦合阻抗的影响。研究表明:当周期变小时色散减弱,耦合阻抗增加;而增大直波导长度时色散变弱,但同时耦合阻抗也会下降。因此较小的周期有利于改善曲折圆形槽波导慢波电路的高频特性。鉴于这种电路的耦合阻抗较低,可以适当地减小直波导长度来提高耦合阻抗。曲折槽波导结合了曲折波导散热能力强、色散特性好、容易加工和槽波导单模工作、低损耗、大尺寸等优点,在毫米波及亚毫米波段的行波管中具有较好的发展前景。

矩形栅慢波系统的理论与实验研究

为了克服单模近似法在分析矩形栅慢波系统高频特性时的局限性,采用了一种新的方法,即在表示槽区内的场时,保留其高次项,表为一无限本征驻波之和的形式,利用场匹配法得到其色散特性,进而求得耦合阻抗。然后针对矩形栅慢波系统进行了数值计算,并分析了金属栅的几何尺寸对系统高频特性的影响,以作为器件设计的参考。设计出3cm、8mm波段的矩形栅高频结构模型,进行实验测量,得到的实验值与理论值符合良好。

波在磁化周期等离子体中的传播特性

电磁波与等离子体之间存在极为丰富的相互作用现象,对电磁波的传播构成重大影响。该文研究了在磁场指导下,对电磁波在密度周期变化的磁化等离子体中的传播特性,进行了理论分析并导出色散方程,通过数值计算分析了等离子体密度变化分别对电磁波传播特性的影响。计算结果表明密度n1变化对左、右旋波的截止频率影响不大,而n0的变化对左旋波的截止频率影响大,对右旋波的通带宽度影响大。并发现密度周期变化磁化等离子体构成一周期慢波系统,在该系统中明显出现慢波,这可能对注波互作用产生重大影响。

大功率太赫兹返波管的数值模拟研究

为了提升传统超高频小功率返波管的工作频率和输出功率,提出了一种过模表面波太赫兹返波管的紧凑结构.其中,慢波系统是在一段过模圆柱波导内壁沿圆周方向平行挖去若干个均匀环形槽构成的,相邻槽间距固定不变.该结构较之传统的单模结构能有效地降低管内电场强度、避免场击穿,提高系统在太赫兹频段的功率容量.采用数值模拟的方法对该慢波系统的结构参数进行了筛选,最终选取波导内半径为2 mm、槽深为0.2 mm、槽宽为0.6 mm、单周期长度为1 mm,共采用17个周期.利用2.5维粒子模拟程序对系统进行了热测实验,在电子注电压为550 kV、电子注电流为350 A的条件下,模拟得到了14.4 MW的峰值功率输出,其能量转换效率达到7.5%,振荡频率高于0.14 THz,时域波形及频谱特性良好.

新型反绕双螺旋线慢波系统的分析与设计

基于降低工艺难度的目的,提出了一种新型反绕双螺旋线慢波系统,该系统的正绕反绕螺旋线半径不等。利用3维电磁软件CST MWS仿真分析了结构参数对色散和耦合阻抗的影响。结果表明:耦合阻抗在螺旋带内半径较大时没有明显下降;减小螺旋带宽度有利于降低相速度和提高耦合阻抗;在一定范围内,相速度随螺距的减小而增大。在此基础上,结合工程要求设计了8 mm波段行波管的新型反绕双螺旋线慢波系统,耦合阻抗达到21Ω,工作电压约为20 kV,同时由于电子通道半径较大,降低了对电子光学系统的要求;纵向翼片加载的引进较为有效地展宽了带宽。

脉冲空间行波管的研制

脉冲空间行波管主要用于环境卫星、微波遥感卫星、海洋卫星等军民用卫星系统,本文主要介绍了中国科学院电子学研究所脉冲空间行波管的研制进展,包括栅控电子枪、双渐变慢波系统、高匹配性能输能结构、多级降压收集极的设计方案、样管测试结果及环境试验情况等。

曲折矩形槽波导慢波系统的高频特性

对曲折矩形槽波导新型慢波系统的高频特性进行了研究,通过理论分析和数值计算,得到了它的色散曲线和耦合阻抗,并分析了结构参数变化时对色散特性和耦合阻抗的影响。曲折矩形槽波导结合了曲折波导散热能力强、色散特性好、容易加工和矩形槽波导单模工作、低损耗、大尺寸等优点,因此这种新型的慢波系统有可能在毫米波及亚毫米波段的行波管中具有较好的发展前景。

0.34THz折叠波导行波管设计及流通管实验

以0.34 THz折叠波导行波管为研究对象,分析了慢波结构的色散特性、耦合阻抗、冷损耗特性和工作模式等,并按优化后折叠波导慢波结构的要求设计电子光学系统,进行流通管实验,得到电子注通过率大于80%的实验结果。最后对输入输出结构进行优化设计,满足中心频率为0.345 THz,带宽大于10 GHz,输出功率大于20 mW的0.34 THz折叠波导行波管设计要求。

0.22THz折叠波导行波管部件设计与加工

以理论推导和三维模拟仿真设计为基础,设计优化了0.22THz折叠波导行波管电子枪、慢波结构、永磁聚焦系统、输入/输出结构、收集极等部分,并结合大量的工艺实验,探索和研究了各种精密加工方法和组装焊接工艺,最后完成了符合这些部分设计要求的高精度零件加工和组装焊接样品。