共查询到20条相似文献,搜索用时 15 毫秒
1.
A study of ocean-like surface thermal emission and reflection using Voronovich's small slope approximation 总被引:2,自引:0,他引:2
Monte Carlo simulations are used to compute average direct surface thermal emission and reflected atmospheric radiation using the "active" small slope approximation of Voronovich. The surfaces considered are realizations of an ocean-like spectrum and contain features ranging from 64 to 0.5 electromagnetic wavelengths. The parallel computing approach of the study is described, and results are compared with predictions from the commonly applied "two-scale" theory of sea emission. Results show a reasonable level of agreement in a small height surface case, which degrades as the surface height is increased. 相似文献
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基于小斜率近似方法推导了极坐标系下介质粗糙面的双站散射系数和后向散射系数计算公式.为验证小斜率近似方法的准确性,针对二维高斯介质粗糙面,计算了双站散射系数并将得到的数值结果与实验测量数据和基尔霍夫近似方法计算结果进行了对比分析,结果表明:小斜率近似方法的结果和实验数据吻合较好.同时对不同入射角下散射系数的角分布及粗糙度和均方根斜率对散射系数的影响进行了讨论分析. 相似文献
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For lowG/T ship-based earth stations in future maritime satellite communications, the effect of multipath fading due to sea surface reflection will be very important at low elevation angles. However, a practical model of theL -band multipath fading for fade prediction has not been available so far. A practical fading model is presented based on the shadowed Kirchhoff approximation theory for the coherent and incoherent components of the scattered power as a function of sea surface conditions. Using this model, theoretical fading depths are presented as a function of elevation angle, wave height, and antenna gain. The results indicate that intense fading occurs for wave heights greater than 50 cm, and the dependence on wave height is small under these conditions atL -band frequencies. Theoretical results presented agree well with experimental results obtained by field experiments. 相似文献
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Reverberation chambers (also called mode-stirred chambers) are multimoded cavities that are used for radiated emissions or immunity measurements. A reflection coefficient method is used to derive the quality factor (Q) of reverberation chambers of arbitrary shape. The results are applicable to walls of general materials, but reduce to the previous result for highly conducting walls with small skin depth. The reflection coefficient method is also used to derive the decay time of reverberation chambers 相似文献
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A new improved six-port circuit for complex reflection coefficient measurements is presented. It consists of two six-port directional couplers. Assuming the components to be ideal, it is shown that the described six-port circuit has optimal properties for accurate determination of complex reflection coefficients. A six-port branchline coupler is briefly described. 相似文献
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Tian Buning Tang Jiaming Liu Qizhong 《电子科学学刊(英文版)》2001,18(4):359-362
A novel method for precise measurement of complex reflection coefficient using a four-port reflectometer is presented. First, three new complex system constants are introduced, which depend only on the scattering parameters of the four-port reflectometer. Therefore, the stability of the reflectometer is greatly improved. Then, these complex system constants are used to determine the complex reflection coefficient T of the device under test by calibrating the reflectometer. Finally, a four-port reflectometer comprising a magic tee and a power detector is constructed and excellent experimental results are obtained. 相似文献
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Multipath fading in maritime satellite communications may be caused by a combination of sea surface reflection and tropospheric effects such as ducting and scintillations. Among them, multipath fading due to sea reflection is dominant when receiving satellite signals by use of a wide beamwidth antenna. In this paper, fade duration statistics of multipath fading due to sea surface reflection are analyzed using the data obtained by on-board experiments on theL -band (1.54 GHz). Results indicate that the mean value of fade duration and fade occurrence interval can be determined from the fading power spectrum with fairly good precision, and that the probability density function for a given time percentage, ranging from 50 to 99 percent, approximates well with the exponential distribution. Finally, based on the results obtained, a simple method for estimating the mean values of fade duration and fade occurrence interval is presented. 相似文献
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针对海杂波背景下雷达对海面弱小目标探测技术难题,提出一种基于时频脊-Radon变换的帧平滑双特征检测方法。该方法首先采用分块白化方法对海杂波进行抑制,根据抑制后海杂波单元与目标单元在时频域二维平面呈现的不同能量分布特征,对时频脊做Radon变换并在变换域特征空间中提取出峰值和频宽特征。考虑到实际雷达采用的相干脉冲数通常较少(大多情况下为64个或更少),易导致特征不稳定,进而影响海杂波与目标可分性,为此,通过多帧扫描历史数据和当前帧数据的综合应用,对特征做帧平滑处理以增强可分性。最后采用凸包分类算法,在双特征平面进行融合检测。经2级和4级海况实测数据验证,在同等参数条件下,本文检测方法相比已有基于时频三特征的检测方法、频域CFAR检测方法和分形特征检测方法具有更好的检测性能。 相似文献
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针对海面上方低空飞行慢速小目标探测问题,采用Kirchhoff近似(KA)和矩量法(MoM)的混合方法研究了时变海面与其上方运动目标的后向散射回波的多普勒特性。分析了海况参数、入射角、目标运动速度、目标与海面之间的距离以及目标截面形状等对后向散射回波多普勒特性的影响。这项研究对于海面与目标耦合散射机理的分析以及海杂波背景下低飞慢速小目标的检测与识别具有重要意义。 相似文献
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WU Feng 《半导体光子学与技术》1995,(Z1)
AnalysisofreflectioncoefficientforcoatedopticalwaveguidedevicesWUFeng(ChongqingOptoelectronicsResearchInstitute,Yongchuan6321... 相似文献
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Tzong-Dar Wu Chen K.S. Jiancheng Shi Fung A.K. 《Geoscience and Remote Sensing, IEEE Transactions on》2001,39(9):2040-2050
In the development of wave scattering models for randomly dielectric rough surfaces, it is usually assumed that the Fresnel reflection coefficients could be approximately evaluated at either the incident angle or the specular angle. However, these two considerations are only applicable to their respective regions of validity. A common question to ask is what are the conditions under which we would choose one or the other of these two approximations? Since these approximations are basically roughness-dependent, how can we handle the in-between cases where neither is appropriate? In this paper, a physical-based transition function that naturally connects these two approximations is proposed. The like-polarized backscattering coefficients are evaluated with the model and are compared with those calculated with a moment method simulation for both Gaussian and non-Gaussian correlated surfaces. It is found that the proposed transition function provides an excellent prediction for the backscattering coefficient in the frequency and angle trends 相似文献
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The port reflection coefficient method (PRCM) is proposed for the treatment of multi-port microwave network systems. The theory is meaningful because in combination with other available numerical techniques, it can provide several possible ways for simplifying and solving complicated multiport problems. The PRCM also suggests an approach for the measurement of scattering parameters, since it requires only the measurement of reflection coefficients at partial ports of the system. The efficiency and versatility of the method are verified through various numerical examples, including waveguide H-plane right angle bend, E-plane T-junctions, and multi-port power dividers. A special case of this method yields the well-known transverse resonance approach 相似文献
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WUFeng 《半导体光子学与技术》1995,1(1):9-19
From an ordinary condition,using a full three-dimensional model theory and an infinite perturbation expansion method,an exact solution of the re-flection coefficient for the coated narrow stripe-geometry optical waveguide devices has been derived.All six components and the vector property of the electroma-gnetic field have been considered.The results are suitable for the symmetric and asymmetric waveguides. 相似文献
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应用双尺度方法(Two-Scale Method,TSM)计算了海面的后向散射系数(Backscattering Coefficient,BSC).由于实测的海面散射系数在大角度与理论不相符,尤其是水平(Horizontal,HH)极化,中等尺度的碎浪模型被用来对海面散射系数进行修正.通过对不同参数的中等尺度碎浪散射系数进行统计平均,可以得到碎浪的平均散射系数.运用碎浪的覆盖率模型,将碎浪模型与海面的散射系数进行结合,得到了含碎浪的海面散射系数修正模型.结果表明,该模型在大入射角下能对HH极化有明显的修正作用,使其与实验数据更为吻合.对于垂直(Vertical,VV)极化,TSM计算的结果本身就与实验数据吻合得较好,碎浪也没有对其有明显的修正. 相似文献
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A numerically derived solution of the diffraction coefficient for a source mounted on a perfectly conducting planar surface which is smoothly terminated by a circular cylinder is obtained using the hybrid approach which combines the moment method (MM) with the geometrical theory of diffraction (GTD). This solution is valid not only in the region away from, but also in the region near, the shadow boundary. The accuracy and usefulness of this solution is demonstrated as various structures are treated using it. 相似文献
18.
An efficient two-scale model for the computation of thermal emission and atmospheric reflection from the sea surface 总被引:6,自引:0,他引:6
An efficient implementation of the two-scale model of sea surface thermal emission and atmospheric reflection is described. The model is applied in a study of the reflection of downwelling atmospheric radiation. Results show that reflected downwelling radiation can increase azimuthal variations of total observed brightnesses. 相似文献
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This paper presents a simple but effective method for the analysis of open-ended waveguides. The method begins with the introduction of a large waveguide to approximate the half-space. In order to avoid the convergence problem lossy dielectric is assumed to homogeneously fill the large waveguide. After obtaining a number of convergent data for different values of the loss tangent an extrapolation technique is employed to calculate the solution to the original problem-a waveguide terminated by an infinite conducting range and radiating into a lossless or low-loss half-space. Numerical results are given to show the validity of the proposed method. The behavior of the effect of the loss tangent on the size of the large waveguide and on the final results are also examined 相似文献