共查询到19条相似文献,搜索用时 140 毫秒
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根据表面波在非磁化等离子体柱中的色散关系,理论计算得到存在电子-中性原子碰撞、径向与轴向等离子体密度非均匀分布条件下m=0角向模表面波波矢实部与虚部随信号频率、等离子体密度的变化关系.然后利用波矢的实部与虚部、等离子体柱天线表面指数分布电流模型、等离子体阻抗,推导得到等离子体柱天线的辐射方向图随信号频率、等离子体密度的变化关系;最大增益、天线辐射阻抗随信号频率的变化关系;天线径向能量辐射随等离子体密度的变化关系.理论计算结果表明等离子体柱天线辐射方向图随信号频率、等离子体密度的改变而变化非常明显,信号频率对最大增益、天线辐射阻抗的影响显著;同时,这些理论计算结果与他人实验实测结果吻合,这对于设计高精度要求的等离子体天线提供了重要的理论参考价值. 相似文献
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研究了太赫兹波通过均匀磁化等离子体的传播特性,给出了太赫兹波衰减和相移随等离子体密度、碰撞频率、太赫兹波频率和磁感应强度的变化规律。等离子体电子密度越大,衰减和相移越大;随着碰撞频率的增大,电磁波的衰减先增加到峰值后逐渐减小,且随着磁感应强度的增加,衰减的峰值变大,峰值向碰撞频率减小的方向移动;当电子碰撞频率接近电磁波频率时等离子体对右旋极化波的衰减达到极大值。太赫兹波频率增大,衰减逐渐减小,而相移先增加后逐渐减小。 相似文献
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The radiated power of an electric dipole antenna in a thin, dissipative, infinite conical plasma sheath is analyzed. The electromagnetic fields are represented by contour integrals, and the radiated power is calculated according to the method of Baños et al. The sheath is characterized by a single parameter, which is proportional to the integrated electron density and depends inversely on the electron collision frequency. The radiation pattern is distorted from the form of the free-space dipole pattern because of the interaction between the primary dipole fields and the fields induced on the surface of the plasma sheath. In most cases it is found that for small electron densities, electron collisions attenuate the induced surface fields so that the patterns approach their free-space form. For larger electron densities, the pattern has a characteristic heart shape for zero collision frequency. The pattern increases in magnitude, while retaining the same form, as the collision frequency increases from zero. As the collision frequency is further increased, the pattern approaches the free-space pattern in magnitude and form. 相似文献
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The problems of a gap-excited finite-sized prolate spheroidal antenna, with and without a confocal prolate spheroidal vacuum sheath, operated in a uniform cold and in a uniform warm lossy plasma medium, have been considered by applying boundary value problem techniques. The dependence of the input admittance, the current distribution, and the radiation pattern, upon the collision frequency, the electron temperature, the length of the antenna, the length-to-radius ratio for the antenna, the ratio of the plasma frequency to the operating frequency, and the thickness of a vacuum sheath have been investigated. Admittance curves are given from which the input admittance of a finite linear antenna can be estimated for a wide range of operating conditions and length-to-radius ratios. Conductance and susceptance maxima, dependent upon the vacuum sheath thickness, have been observed when using the cold plasma model foromega < omega_{p} . When using the warm plasma model in conjunction with the boundary condition that the normal component of the fluid velocity is zero at the antenna surface and at the vacuum sheath surface, the radiation resistance of the antenna is increased significantly for the parameters considered. 相似文献
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A quantitative laboratory experimental investigation has been conducted on the distortion of the main far-field radiation pattern of a horn antenna situated behind a layer of isotropic plasma. The power radiation pattern and phase for orthogonal components of the radiation transmitted through the plasma were investigated for various plasma properties. The experimental results were compared to theory based on the reciprocity theorem and good agreement was obtained. The major features are a gradual attenuation and distortion of the radiation pattern for plasma electron densities below the critical density and a rapid change in the radiation pattern with severe attenuation in the region of the critical electron density followed by "cut-off" at still larger electron densities. No appreciable polarization change of the energy radiated by the antenna is introduced by the plasma. 相似文献
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C. S. Yeh N. Urimindi Jin Liu G. A. Evans J. K. Butler 《Journal of Infrared, Millimeter and Terahertz Waves》1993,14(4):885-892
This paper concerns the experimental characteristics of metal coated dielectric waveguides with a rectangular surface corrugation. Waveguide are designed to operate at a second Bragg frequency of 90 GHz. The period, height and the duty cycle of a rectangular grating were calculated using the chosen frequency. A metallic layer of aluminum is sputtered on one side of the slab waveguide. The purpose of the metallic layer is to simulate a layer of high density plasma on the surface of the waveguide similar to that obtained by optical excitation of semiconductor structures. Experiments were performed to examine the far field radiation pattern, attenuation constant and the dispersion relation. Due to the presence of the plasma layer there will be an angular shift in the far field radiation pattern. We have observed angular shifts of about 20? in the radiation pattern of the waveguide before and after coating. Measurements are made in the frequency range of 88–95 GHz. This waveguide structure can be used to design an electronically steerable antenna and an electronic phase shifter operating in the millimeter-wave frequency band. 相似文献
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等离子体天线具有隐身、动态重构等不同于金属天线的独特的物理性质,在卫星遥感、通信、导航领域具有潜在的应用前景。为了研究等离子体频率对天线特性的影响,采用三维电磁仿真软件建立了柱形等离子体天线模型,在此基础上,针对等离子体频率对等离子体天线的S11曲线、方向图、增益等性能的影响进行了仿真分析,并给出了相关结论。 相似文献
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An experimental study of the input impedance of a short cylindrical antenna immersed in a laboratory magnetoplasma is reported. The antenna is fixed in length and is aligned with its axis parallel to the dc magnetic field. Of particular interest is its impedance behavior in the vicinity of the resonance and cut-off conditions of the magnetoionic medium. Independent measurements are made to determine the electron density from the ion-current characteristics of a spherical Langmuir probe and the strength of the applied magnetic field with a Hall-effect probe. Measured impedances are compared with Balmain's theory. Essential features observed experimentally are a peak in the antenna input resistance near the upper hybrid resonance frequency and a peak in the antenna conductance near the cyclotron frequency. An additional small increase in the input resistance is observed near the plasma frequency when the plasma frequency is not close to either the upper hybrid resonance frequency or the cyclotron frequency. These results suggest the possibility of using a short cylindrical antenna as a diagnostic probe for measuring properties of a magnetoplasma such as the electron density and collision frequency. 相似文献
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The development of antenna theory for nonsinusoidal electromagnetic waves has been based on the idealized rectangular pulse. In practice, an antenna that is designed to operate in the mode of an electric hertzian dipole would radiate a pulse that best approximates a Gaussian one when the driving current consists of a linear transient. The principle of radiation of nonsinusoidal electromagnetic waves with the time variation of Gaussian pulses is discussed. The properties of the Gaussian pulse are presented, i.e., the autocorrelation function, energy spectral density, and spectrum. Antenna patterns, such as peak-amplitude pattern, peak-power pattern, energy pattern, and slope pattern are derived for a Gaussian pulse received (or radiated) by a linear array antenna. Computer plots of the derived antenna patterns are presented that show a considerable improvement in the angular resolution capability over that of the antenna patterns that have been derived for a rectangular pulse 相似文献
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The development of a multiturn loop antenna for a police officer's personal radio set is described. The antenna is small, low profile, lightweight, with dimensions of2.7 times 2.7 times 0.7 in high (1.06 times 1.06 times 0.28 cm), and is tunable over the 150- to 170-MHz band. VSWR and radiation patterns are presented with the antenna mounted on a man's shoulder. The shoulder-mounted antenna characteristics are described with conditions where the man is in standing, stooping, and prone positions, with various head and arm movements, and with light and heavy clothing. Radiation patterns are referenced to a 6-in helical whip commonly used by police officers. Radiation patterns also indicate body absorption loss for loop and whip antennas mounted at waist level as compared with shoulder levels. The instantaneous bandwidth is 1.4 MHz for a VSWRleq 3:1 . A dual-frequency model for use in a two-frequency push-to-talk mode, is also shown to be practical. 相似文献