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Time-domain equivalent edge currents for transient scattering 总被引:2,自引:0,他引:2
Time-domain equivalent edge currents (TD-EEC) are developed for the transient scattering analysis. The development is based an the Fourier inversion of frequency domain equivalent edge current expressions. The time-domain diffracted fields are expressed in terms of a contour integral along the diffracting edges for any arbitrary input pulse shape, thereby yielding finite results at the caustics of diffracted rays. The approach also eliminates the need for the evaluation of a convolution integral in the time domain geometrical theory of diffraction (GTD) analysis. The results are compared with the first order GTD results for the transient scattering analysis for a circular disk 相似文献
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The complex resonance frequencies of a scatterer are important elements in target classification and identification. In the singularity expansion method (SEM), the resonances are defined by a homogeneous integral equation whose numerical solution is feasible in the low, but not in the high, frequency range. At high frequencies, the geometrical theory of diffraction (GTD) provides an attractive numerical alternative and, furthermore, incorporates an interpretation of the resonance generation process in terms of multiple wavefront (ray) traversals. Except for extremely simple scatterer configurations, the (damped) complex resonances are known to occupy an entire half of the complex frequency plane. Dominant and higher order creeping wave GTD applied to cylinders and spheres does indeed yield resonances arranged along a sequence of "layers" in that entire half-plane, but multiple edge diffracted GTD applied to flat strips and disks furnishes only a single (dominant) layer. By drawing analogies with higher order creeping waves on a smooth object, the conventional edge diffracted GTD field is here augmented by higher order ray fields undergoing higher order "slope diffraction." Each of these higher order ray fields can be made to satisfy its own resonance equation, which is now found to provide the missing layers, with remarkably accurate values for the resonances when compared, where available, with those calculated numerically by the moment and T-matrix methods. The success of higher order ray diffraction in predicting the complex resonance structure suggests that this mechanism may play a corrective role also in other edge dominated scattering phenomena. 相似文献
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The backscattered fields of a perfectly conducting circular disk are analyzed from a transient signature viewpoint. The significant dominant scattering mechanisms are identified for both principal polarizations at a variety of angles. Particular attention is given to the edge wave. The backscattered field behavior due to an incident plane wave on a perfectly conducting disk is presented. Good agreement was obtained between the eigenfunction and geometric theory of diffraction solutions. The expected mechanisms from first-, second-, and third-order diffractions with an accurate edge wave representation are demonstrated through the use of transient signatures. The most significant error in the geometric theory of diffraction (GTD) solution occurs in time where the nonprincipal plane double diffraction term exists 相似文献
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By including correction terms in inverse powers of the wavenumberk , one may hope to extend the range of applicability of multiple edge diffracted geometrical theory of diffraction (GTD) to lower frequencies, and also to extend thereby the range of validity of the corresponding time domain solutions. The correction can be applied to each of the surface rays in the hierarchy that has been proposed by us recently as a model for multiple interaction between parallel edges separated by a plane surface segment on a two-dimensional perfectly conducting scatterer. The surface rays, which were found to explain the structure of the complex resonances in transient scattering, are excited for each interaction by equivalent line sources, dipole line sources, and their derivatives, with strengths determined from the asymptotic expansion of the edge diffracted field. This procedure is applied in detail toE - andH - polarized plane wave scattering by a perfectly conducting flat strip, up to quadruple diffraction, including consistentO(k^{-2}) corrections with respect to the dominant term. The procedure is applied also to generate corrected multiple diffracted individual surface ray fields, which lead to an improved equation for the complex resonances in the "layer" synthesized in the complex frequency plane by a surface ray of a particular order. Inclusion of the low frequency corrections reduces further the already small discrepancy between the ray optically calculated low frequency resonances and those computed numerically by the moment method. 相似文献
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雷达高距离分辨力需要大带宽发射信号,而雷达发射连续大带宽信号受硬件成本和频谱资源限制。利用多个窄带发射信号进行宽带合成时,由于窄带信号频谱不连续性和步进量的增大,会出现距离旁瓣增大、不模糊距离范围缩小的问题。为解决上述问题,并充分利用不连续或跨波段的频谱资源,提出一种用于宽带聚合的雷达稀疏频率配置方式。通过子频带之间的差分处理,获得等效的连续均匀步进虚拟频率信号,在获得高分辨力的同时避免距离旁瓣增大和距离模糊;对于频率跨度较大的子频带,提出了基于几何绕射理论(GTD)模型的目标散射特性频率一致性校正方法,并仿真分析了不同频率跨度对宽带聚合效果的影响和跨波段宽带聚合的可能性。该研究可进一步为雷达系统的后续兼容研究提供参考。 相似文献
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二维相干极化GTD(CP-GTD)模型能够精确描述高频区雷达目标的电磁散射机理。基于此模型,针对二维ESPRIT方法在色噪声情况下估计精度不高的问题,提出了一种新的二维散射中心参数估计方法。根据二维四阶混合累积量的特点和性质,用其代替观测数据实现色噪声背景下二维CP-GTD模型的位置参数估计,然后通过MUSIC谱峰搜索方法估计散射中心的类型参数,通过最小二乘法估计散射中心的相干极化散射矩阵。该方法能够实现全极化雷达目标的超分辨成像和二维CP-GTD模型参数的正确估计,与现有的二维MUSIC和二维ESPRIT方法相比,改善了估计性能,对色噪声具有较强的稳健性,同时克服了在长观测样本情况下计算量过大的缺陷。仿真和暗室测量数据实验验证了上述结论的正确性。 相似文献
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The axial echo area of a perfecfiy conducting prolate spheroid is derived from an approximate solution to a transient scattering problem. This solution is obtained by modifying the time-dependent back-scattered waveform for a perfectly conducting sphere so as to conform with the spheroid geometry. As a result of the analysis, the echo area vs. source frequency may be predicted over the resonance region. Calculated results for the case of a spheroid with a 2-to-1 axial ratio are compared with experimental data for major axes ranging from 0.318 to 1.59 wavelengths. 相似文献
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几何绕射理论(Geometrical Theory of Diffraction,GTD)模型能够精确描述高频区雷达目标的电磁散射机理.该文在分析雷达回波稀疏特性的基础上,将参数估计问题转化为压缩感知理论中的稀疏信号重构问题,据此提出了一种基于压缩感知的2维GTD模型参数估计方法.该方法首先利用2维傅里叶变换成像确定目标散射中心的支撑区域,然后在支撑区域内对散射中心的GTD参数进行估计,最后利用聚类方法和最小二乘方法对估计结果进行修正.仿真和暗室测量数据实验结果表明,与现有方法相比,所提方法能有效改善模型参数的估计性能,且对提高散射中心类型参数的估计精度更为明显. 相似文献
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The angular spectrum method involves the integral representation of the scattered field in terms of the angular spectra of the pertinent surface currents. Here the angular spectrum method in conjunction with the scattering matrix formulation is used for the diffraction analysis of a thick perfectly conducting half-plane considering both polarizations of incidence. Of particular interest is the scattering behavior by edges of thicknesses less than a wavelength where a geometrical theory of diffraction (GTD) solution is generally not applicable. Several backscatter and bistatic patterns are then presented in this range of thicknesses, and for the backscatter case some are also compared with measured data. It is found that a combination of the angular spectrum method and GTD can be employed for the efficient analysis of an edge of arbitrary thickness. 相似文献
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Surface current and charge density induced on aircraft 总被引:1,自引:0,他引:1
The usefulness of the geometrical theory of diffraction (GTD) in computing the surface current and charge density induced on aircraft is illustrated. This is a high-frequency solution for an arbitrary incident plane wave and fuselage observation points. A pattern is presented for an arbitrary incident plane wave as well as a series of frequency and time domain plots for roll plane incidence. A 3-dimensional pattern is presented for plane wave incidence (as a function of incidence angle) as well as examples of roll plane results in both the frequency and time domain. 相似文献
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Nan Wang 《Antennas and Propagation, IEEE Transactions on》1976,24(4):463-468
A user-oriented computer program has been developed for high frequency radiation and scattering from infinitely-long perfectly. conducting convex cylinders. The analysis is based on the self-consistent geometrical theory of diffraction (GTD). The cylinder is modeled as anN -sided polygon. Two cylindrical waves with unknown amplitudes are assumed to travel in opposite directions on each face of the polygon. The boundary conditions for the corners are applied to set up a matrix equation for2N unknowns (the amplitudes associated with the traveling cylindrical waves). Crout's method is used to solve the matrix equation. Once the amplitudes for the traveling waves are determined, the radiation or scattered field is readily obtained via the usual GTD techniques. Numerical results are presented for radiation and scattering from rectangular, semi-circular, circular, and elliptic cylinders for both principal polarizations. The results show excellent agreement with GTD, moment, and eigenfunction solutions. 相似文献
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《Antennas and Propagation, IEEE Transactions on》2006,54(9):2463-2471
A closed-form analytic solution based on a time-domain (TD) physical optics (PO) approximation is developed for the scattering from a finite second-order surface when illuminated by a transient impulsive plane wave. This TD-PO solution can be applied via a convolution to derive the early time transient fields scattered from the same scatterer that is illuminated by a realistic astigmatic finite-energy pulse. The closed form TD-PO solution is obtained by inverting the corresponding frequency-domain PO solution into TD. This solution can be expressed in terms of reflection and diffraction components of the scattering mechanisms as in other conventional high-frequency asymptotic solutions. Numerical examples are presented to demonstrate its physical phenomenon of the scattering mechanisms. 相似文献