共查询到20条相似文献,搜索用时 109 毫秒
1.
Shunkang Liu 《Journal of Infrared, Millimeter and Terahertz Waves》1997,18(6):1317-1321
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. 相似文献
2.
Shunkang Liu 《Journal of Infrared, Millimeter and Terahertz Waves》2000,21(6):915-920
The characteristics of two kinds of bifilar helix circuit are discussed in this paper. One is alike wound bifilar helix and another is contrawound bifilar helix. Alike wound bifilar helix is often used in O-type backward wave tube (BWO). Owing to wider operating bandwidth, higher interaction impedance and large dimensions, the contrawound helix is suitable for broadband millimeter wave traveling wave tube (MMW TWT). 相似文献
3.
Shunkang Liu 《Journal of Infrared, Millimeter and Terahertz Waves》2002,23(6):899-906
The efficiency enhancement methods for helix and coupled cavity traveling wave tube (TWT) in millimeter wave (MMW) are described. The interaction efficiency has been reached 14.56% by dynamic velocity taper in Ka-band TWT. Efficiency improvement has been carried out by used copper helix for broadband MMW TWT. Owing to a ferruleless coupled cavity TWT used phase-adjusted taper, the interaction efficiency has been increased from 9.6 to 22.6%. Finally, enhancing collector efficiency used multistage depressed collectors is discussed in the paper. These concept and technology of the approach are very useful for tube designer. 相似文献
4.
Shunkang Liu 《Journal of Infrared, Millimeter and Terahertz Waves》2000,21(5):745-750
In millimeter wave band, interaction impedance and efficiency of the ring-bar circuit are higher than helix. Ring-bar traveling wave tubes (TWTs) do not easy yield backward wave oscillation at high operating voltages. Thus ring-bar TWTs can reach higher power lever. On basic of computation of dispersion and interaction impedance, a fast estimation models of RF parameters for MMW ring-bar TWTs are given in this paper. It is available in designing tube to reduce developing period. 相似文献
5.
Shunkang Liu 《Journal of Infrared, Millimeter and Terahertz Waves》1999,20(10):1749-1755
A computation technique for gain, efficiency and output power in broadband millimeter wave helix TWTs from their dimensions is described. The computed results by modeling are good agreement with experimental measurements. It is shown that the method is fast and useful accuracy. It can be used as engineering design for MMW TWTs. 相似文献
6.
《Electron Devices, IEEE Transactions on》1963,10(6):389-393
Coupled-mode theory is employed to describe the interaction between nonuniform electron beams and circuits. It is then applied to determine the start-oscillation conditions of a tapered backward-wave oscillator. It is shown that under high space-charge operating conditions where the coupling to the fast space-charge wave is negligible and for weak circuit tapers, an approximate closed form solution of the coupled-mode equations can be obtained through a Wentzel-Kramers-Brillouin-Jeffreys approximation. The start-oscillation conditions are then determined approximately from such a solution. 相似文献
7.
S. K. Datta Lalit Kumar B. N. Basu 《Journal of Infrared, Millimeter and Terahertz Waves》2008,29(6):608-616
An accurate and simple closed-form formula, for backward-wave start-oscillation condition for a millimeter-wave helix traveling-wave tube amplifier was developed, using an artificial neural network (ANN) algorithm. The analysis considers the effects of circuit loss and also the variation of electron beam diameter corresponding to beam filling. The formula is simple and amenable to easy computation, even using a scientific calculator, and without resorting to exhaustive numerical iterative search followed in conventional analyses and, at the same time, without sacrificing the accuracy in results. The formula was validated against published results, and excellent accuracy was observed. The analysis has been further used for inferring some physical interpretations on the effects of beam-filling factor and circuit loss on the start-oscillation condition of a typical millimeter-wave helix traveling-wave tube. 相似文献
8.
Qingcheng Liu Xingguo Li Dahang Cheng 《Journal of Infrared, Millimeter and Terahertz Waves》2009,30(8):868-876
Building on a mathematical model of a single beam millimeter wave (MMW) radiometer on a hi-tech bomb, system parameters are
proposed and simulated for a three beam MMW radiometer. Scanning rate, falling rate and other parameters are put forward in
the context of a novel conical scan MMW detector. The demodulated signals of detecting a target are simulated. With this approach
the target radial center positioning accuracy can be improved. The simulation results indicate that the radiometer has favorable
performances, such as a wide range of detection, high radial positioning accuracy and reacquisition target ability in the
most adverse condition that the target’s radial movement is outwards. 相似文献
9.
Shunkang Liu 《Journal of Infrared, Millimeter and Terahertz Waves》2003,24(3):335-347
In millimeter wave range, high-power traveling wave tube (TWT) is a key device with broadband and high-power amplification. Basis of comparing traditional and new type slow wave circuits for high-power TWT in MMW, analysis and computation of propagating and RF performance for folded wave circuit are carried out. Theoretic calculation and experimental test show that folded wave circuit is an ideal slow wave structure for broadband and high-power TWT in MMW. There is extreme wide application for the circuit in high-power TWT. This development possesses important consult value to designer for MMW power amplifiers. 相似文献
10.
In this paper, the frequency selective reflection characteristics of dielectric periodic structures with arbitrary groove profiles are analyzed by a method which combines the multimode network theory with the rigorous mode matching procedure. Emphasis is placed on the discussion about the effect of the different groove profiles, such as rectangle, trapezoid, increasing cosine and triangle, on the reflection characteristics of the millimeter wave (MMW) frequency selective surface (FSS). Some useful guidelines for the design of the MMW dielectric FSS are thus suggested. Moreover, the physical explanation of the related wave phenomenon is given. 相似文献
11.
12.
Jim-Wein Lin Jhih-Min Wun Jin-Wei Shi Ci-Ling Pan 《Journal of Infrared, Millimeter and Terahertz Waves》2014,35(10):813-822
We conducted a comparative study of two schemes of photonic generation and switching of few-cycle sub-THz or millimeter wave (MMW) pulses by use of a photonic-transmitter-mixer (PTM) module with a broadband and high-power near-ballistic uni-traveling carrier photodiode (NBUTC-PD). In the first scheme, we performed all-optical ultra-fast switching (bias modulation) of the PTM injected with a 93 GHz optical local-oscillator signal. Sub-2-cycle short MMW pulses with central frequency at 93 GHz were generated. To compare, in scheme 2, we employed femtosecond optical short pulses to directly excite the PTM under a DC bias (optical modulation). The former approach is shown to be capable of providing much less signal distortion and much shorter pulse duration than the latter. 相似文献
13.
The current distribution, the near field, and the far field of helical antennas are examined. It is found that the application of the helix as an endfire radiator is dependent on two higher Order modes of the helix wave functions. This differs from the application of the helix as a slow wave structure in a traveling wave tube where the lowest order mode of the helix wave functions is utilized. 相似文献
14.
Shunkang Liu 《Journal of Infrared, Millimeter and Terahertz Waves》2003,24(5):629-638
The pill-box and block RF windows for millimeter wave (MMW) tubes are presented. The pill-box window is suitable for broadband MMW tubes. And the block window can be used for high power tubes in short MMW. The equivalent circuits for two windows are given. To reach better match characteristics in wider operating bandwidth, the optimum design methods for pill-box and block window in MMW tubes are described in this paper. The testing results show that the theoretic computation is fast and useful accuracy. The design methods possess references value to designer for MMW tubes. 相似文献
15.
通过收集大量的毫米波图像并建立相应的人体数据集进行检测,提出基于Faster R-CNN深度学习的方法检测隐藏于人体上的危险物品。该方法将区域建议网络和VGG19训练卷积神经网络模型相结合,构建了面向毫米波图像目标检测的深度卷积神经网络。为了提高毫米波图像的处理能力,采用Caffe深度学习框架在图形处理单元上进行训练和测试。实验结果证明了基于Faster R-CNN深度卷积神经网络的目标检测方法能有效检测毫米波图像中的危险物品,并且目标检测的平均准确率约94%,检测速度约为6 frame/s,对毫米波安检系统的智能化发展有着极其重要的参考价值。 相似文献
16.
17.
Sezginer A. Shun-Lien Chuang Jin Kong 《Antennas and Propagation, IEEE Transactions on》1983,31(5):732-739
Electromagnetic wave scattering by a tape helix of infinite extent is studied by using Floquet wave expansions for the guided modes and scattered fields. The solution reduces to earlier results as a special limiting case for normal incidence on a sheath helix. The current induced on an infinite helix computed by the presented technique bears close resemblance to the current induced on a long but finite helix as computed by Galerkin's method. The spatial frequency spectrum of the induced current is plotted to show the dominance of the spatial harmonics that are phase matched with the guided modes of the helix. Azimuthal patterns of the scattered field are included to illustrate that interference increases as the diameter of the helix is increased. 相似文献
18.
装甲目标毫米波辐射温度的建模与计算 总被引:5,自引:0,他引:5
在被动毫米波探测原理的研究基础上,建立了辐射计天线温度模型与输出信号模型,对装甲目标进行了实战条件下的毫米波辐射温度计算与分析.指出在进行雷达隐身的同时,必须进行针对被动探测的毫米波被动隐身技术研究,即毫米波辐射特性的控制. 相似文献
19.
《Electron Devices, IEEE Transactions on》1964,11(1):31-37
The effects of nonuniformities in the circuit phase velocity and the beam potential on the start-oscillation conditions of an O-type backward-wave oscillator (BWO) are investigated. The nonuniformities include linear, quadratic, and exponential circuit phase velocity tapers and beam potential gradients. It is shown that for weak circuit phase velocity tapers or voltage gradients the start-oscillation current may be lower than that of a uniform tube; however, when the taper or gradient is made stronger than a particular value which depends on the operating parameters, a no-oscillation region results. The latter result indicates that such nonuniformities may be utilized to suppress backward-wave oscillations in forward-wave amplifiers. 相似文献