共查询到17条相似文献,搜索用时 62 毫秒
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高超声速飞行器再入地面的过程中,其周围等离子体的电子密度是非均匀且随时间变化的.对于不同的再入高度,飞行器周围的温度和压强也会发生改变.因此,研究电磁波在时空非均匀等离子体鞘套中的传播特性意义重大.首先建立了时变非均匀的等离子体鞘套模型,然后通过经验公式得到温度、压强与碰撞频率三者的关系.采用时域有限差分方法计算了太赫兹波段中不同电子密度弛豫时间、温度、压强时的反射系数、透射系数和吸收率.研究结果表明:在太赫兹波段中,电子密度的弛豫时间越长,温度越高,压强越大,电磁波越容易穿透等离子体;弛豫时间越短,温度越低,压强越小,等离子体对电磁波吸收率的变化越明显.这些结果为解决"黑障"问题提供了理论依据. 相似文献
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针对临近空间飞行器的黑障问题,根据模拟的RAM C-III飞行器周围的流场分布结果,计算了等离子体电子密度和碰撞频率,并根据其分布建立了非均匀的等离子体模型。在此基础上,利用散射矩阵方法分析了太赫兹波在等离子体中的传输特性随着等离子体密度、等离子体厚度、等离子体碰撞频率的变化以及外加磁场对传输特性的影响。结果表明,太赫兹波的传输损耗随着等离子体电子密度和等离子体厚度的增加而增加,而碰撞频率的增加会使得透射率先减小后增加。在外加磁场的作用下,左旋太赫兹波的传输特性会得到改善;而对于右旋太赫兹波,磁场的施加会引入吸收峰,并且随着磁感应强度的增加向高频方向移动。 相似文献
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较大的传输路径损耗限制了太赫兹无线通信在大气中的传输距离,要想实现地面与卫星之间太赫兹波的长程传输,必须先找到低衰减的大气透明窗口。本文结合我国大气分布特点,通过大气辐射传输模型工具am(atmospheric model)对大气吸收衰减建模进行分析,从中选定适合我国地面与卫星太赫兹通信的理想地基站点;利用真实大气数据和分层传输理论,计算了地面与卫星之间太赫兹通信的总路径损耗,结合信号发射功率、天线增益、信噪比、噪声功率值和相应的路径衰减阈值,给出了天线增益分别为0~100 dBi时10~15 THz频段内的总可用带宽和大气窗口;通过将高海拔平台作为地面与卫星之间太赫兹通信的中继链路,给出了1~15 THz频段内的可用大气窗口,为我国地面与卫星通信链路的建立、地基站点和通信频段的选取提供了理论和数值参考。 相似文献
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在已有大气传输模型的基础上,发展了新的太赫兹波大气传输衰减与色散模型,对宽频太赫兹波在真实大气中传输的衰减和色散特性进行了数值模拟研究.改进太赫兹时域光谱技术,对0.3—2.0 THz频段太赫兹波的大气传输特性进行了透射光谱测量,并得到了一组连续吸收参数.比对发现实验窗口区强度和吸收峰的位置都与计算结果符合得很好.据此选取了三个可行的信道:340,410和667 GHz窗口区,利用线性色散理论和无线通信原理分别从物理上精确地计算了这些信道的群速色散参数和信道容量,并分析了影响最大传输数据率的因素-天线增益.研究结果表明:太赫兹波大气传输1 km时,这三个信道群速色散很小,信号不易被展宽;最大传输速率达十几Gbps,高于单模光纤,但需要更高的天线增益. 相似文献
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针对黑障区高速飞行器测控通信研究需求,在激波管设备上开展了Ka波段毫米波与太赫兹波在等离子体中传输特性的实验研究,获得了不同电子密度和碰撞频率的等离子体中传输衰减特性实验数据。采用辅助差分方程的时域有限差分(ADE-FDTD)方法对实验进行了数值模拟,数值模拟结果和实验结果有很好的一致性。实验结果和数值模拟结果均表明:太赫兹波信号在相同的实验等离子体中传输衰减比毫米波信号小得多,具有更强的穿透等离子体能力;毫米波与太赫兹波信号在等离子体中传输衰减量随着等离子体电子密度的增加而增加,二者的差值也增加;太赫兹波能够作为解决高密度等离子体中电磁波传输的有效技术手段。 相似文献
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P. F. Miller H. A. Gebbie 《International Journal of Infrared and Millimeter Waves》1996,17(10):1573-1591
Measurements made in an untuned resonator by Fourier Transform Spectroscopy of atmospheric aerosols are explained by a pumped phonon model due to Fröhlich. 相似文献
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Shunkang Liu 《International Journal of Infrared and Millimeter Waves》1996,17(1):121-126
The equivalent circuit and design method for a RF window in millimeter wave band are presented. Computation and experiment show that matching band of the RF window is wider. It can be used as output window for broadband millimeter wave tubes. 相似文献
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Liu Shunkang 《International Journal of Infrared and Millimeter Waves》1994,15(5):857-860
RF Window of millimeter wave tubes becomes very thin because of extreme high frequency, so that power capacity of the window is limited, manufacturing is difficult and it easy leaks. The equivalent circuit and computation are given for a type of ceramic block RF window with compensating irises. This RF window has higher power capacity, compact mechanical strength, easy manufacturing and airtight welding. The testing results show that the design method is fast and useful accuracy. 相似文献
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S. Saitoh H. Tanaka A. Ono Y. Furuhama T. Manabe T. Ihara 《International Journal of Infrared and Millimeter Waves》1986,7(6):795-812
The attenuation of 245.52 GHz millimeter wave was measured through a near ground horizontal path in order to study the anomalous water vapor absorption at the window region. The result demonstrates that the attenuation coefficient includes the quadratic dependence on the water vapor density. The quadratic component of the water vapor density in the expression of the attenuation was assumed to arises from the contribution of water dimers alone, then the concentration of water dimers was estimated adopting the published theoretical water dimers absorption coefficient. The obtained concentration was 0.062% of monomers in number when the water vapor density is 7.5 g/m3. This concentration is in agreement with the published result obtained by way of another method. 相似文献
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Monte Carlo simulation for millimeter wave propagation and scattering in rain medium 总被引:3,自引:0,他引:3
Wu Zhensen Yan Yi Chen Lihong 《International Journal of Infrared and Millimeter Waves》1992,13(7):981-994
As the operating frequencies of communications systems more higher into the millimeter wave range, the effects of multiple scattering in precipitation media become more significant. This paper treats the problems of electromagnetic multiple scattering in rain medium by the Monte Carlo method. The em wave is regarded as a Markov chain of photon collisions in a medium in which it is scattered and absorbed. For the sake of simplicity, the polarization is not taken into account, the above mentioned problems are described by the scale integro-diffierential equation of transfer. When the plane wave through a random medium with particle size distribution, the technique of weighted average is used to characterize the radiation intensity, including average scattering, absorption coefficients and phase function. The Monte Carlo simulation algorithms are done for the rain attenuation and reflectance at millimeter wavelength region. Our computational results are in good agreement with experimental data of rain attenuation. 相似文献