A study of ocean-like surface thermal emission and reflection using Voronovich's small slope approximation

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.     

高斯介质粗糙面电磁散射的小斜率近似方法

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.     

分形海面电磁散射特性的基尔霍夫近似

利用二维Weierstrass带限函数模拟了粗糙海面的形状,讨论了风速、粗糙度等参量对海面形状的影响;针对模拟的分形海面形状,从亥姆霍兹（Helmholtz）积分出发,利用基尔霍夫近似推导了二维分形海面的电磁散射系数,并进行了数值模拟,同时对数值模拟结果进行了分析,讨论了海面形状对电磁散射的影响,所得结论可用于目标探测技术的研究。     

Characteristics of L-band multipath fading due to sea surface reflection

For lowG/Tship-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.     

A reflection coefficient derivation for the Q of a reverberationchamber

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     

Improved six-port circuit for complex reflection coefficient measurements

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.     

Analysis of reflection coefficient for coated optical waveguide devices

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.     

Port reflection coefficient method for solving multi-port microwavenetwork problems

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     

Fade duration statistics ofL-band multipath fading due to sea surface reflection

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.     

Analysis of reflection coefficient for coated optical waveguide devices

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A transition model for the reflection coefficient in surfacescattering

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     

粗糙海面三维目标电磁散射的快速估算方法

本文使用物理光学法(PO)与区域投影法(AP),结合计算机图形学技术,将两面角反射器的计算原理应用于目标与海面之间的多次散射计算.给出了一种快速判定三维空间内三角形面元是否相交的方法以加速射线追踪.针对Pierson-Moscowitz谱生成的海面,考虑海水的介电特性与海况的影响,计算了不同海况下的三维目标散射特性.并同文献结果进行了比较,表明本文的方法具有较好的准确性.     

A diffraction coefficient for a cylindrically truncated planar surface

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.     

An efficient two-scale model for the computation of thermal emission and atmospheric reflection from the sea surface

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.     

电小尺寸凹槽的远区数值绕射系数

应用时域有限差分（FDTD）方法和时域加窗技术从物体的时域散射场中分离出劈和凹槽一类散射中心的贡献,计算其远区数值绕射系数。对于电小尺寸凹槽的远区数值绕射系数,结合微扰法给出了其计算结果。     

A simple method for calculating the reflection coefficient ofopen-ended waveguides

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     

Backscattering coefficient of a perturbed sinusoidal surface

A coherent model for scattering from a randomly perturbed periodic surface is developed using the Kirchhoff approximation. It is intended to model wave scattering from ground surfaces with row directions. Results are illustrated and compared with an incoherent scatter model and measured backscattering angular curves from ploughed fields.     

A PML using a convolutional curl operator and a numerical reflection coefficient for general linear media

A general time domain representation of the Chew and Weedon [1994] stretched coordinate perfectly matched layer (PML) absorbing boundary condition is described. This new approach mathematically operates on the spatial field derivatives and allows the PML update equations to be trivially derived from any set of general linear medium update equations. A method for calculating the frequency dependent reflection coefficient for this form of the PML is derived for general linear media. Two and three dimensional numerical test results, which validate the calculation of the reflection coefficient, are presented. The range of numerical tests include the PML matching of free space, a magnetoplasma, and a free space waveguide. Improving the reflection coefficient is examined.     

Power reflection coefficient analysis for complex impedances in RFID tag design

Kurokawa's method of calculating the power reflection coefficient from the Smith chart in the situation when one complex impedance is directly connected to another is applied to passive RFID tag design, where power reflection is important, as it determines the tag characteristics. The performance analysis of a specific RFID tag is presented together with experimental data, which is in close agreement with the theory.     

The “packing” and the “scheduling packet”switch architectures for almost all-optical lossless networks

This paper proposes two almost all-optical packet switch architectures, called the “packing switch” and the “scheduling switch” architecture, which when combined with appropriate wait-for-reservation or tell-and-go connection and how control protocols provide lossless communication for traffic that satisfies certain smoothness properties. Both switch architectures preserve the order of packets that use a given input-output pair, and are consistent with virtual circuit switching, The scheduling switch requires 2klogT+k² two-state elementary switches (or 2klogT+2klogk elementary switches, if a different version is used) where k is the number of inputs and T is a parameter that measures the allowed burstiness of the traffic. The packing switch requires very little processing of the packet header, and uses k²logT+klogk two-state switches. We also examine the suitability of the proposed architectures for the design of circuit switched networks. We find that the scheduling switch combines low hardware cost with little processing requirements at the nodes, and is an attractive architecture for both packet-switched and circuit-switched high-speed networks