Scattering from a large body with cracks and cavities by the fast and accurate finite-element boundary-integral method

A large body with cracks and cavities is a typical structure widely existing in realistic targets. In this paper, a newly developed fast and accurate finite-element boundary-integral (FA-FE-BI) method is applied to compute scattering by this kind of scatterer. A thorough analysis on this FA-FE-BI numerical technique is presented, clearly demonstrating that this technique has computational complexity O(N log N) and memory requirement O(N) (N is the total number of surface unknowns). An inward-looking approach is employed as a preconditioner to speed up the rate of convergence of iterative solvers for this structure. Under these techniques, a powerful code is developed for this kind of scatterer whose accuracy, efficiency, and capability is well confirmed by various numerical results.     

Scattering analysis of high performance large sandwich radomes

Large radomes are assembled from many panels connected together forming joints or seams. When the panels are type A sandwiches that are optimized for minimum transmission loss over moderately narrow bandwidths, the seams and joints introduce scattering effects that can degrade the overall electromagnetic performance. Tuning the dielectric seams with conductive wires and optimizing their geometry is, therefore, crucial to enhancing the electromagnetic performance of the radome. The authors address the problem of systematically tuning the dielectric seams and present both numerical and experimental results to illustrate the tuning procedure. Included are results showing the effect of the tuning of the radome on the radiation of an enclosed aperture of circular or elliptic shape     

复杂电大开口腔体的高功率微波防护分析

提出考虑传输衰减的高功率微波（HPM）激励模型,基于镀膜透明介质结构设计流程,给出了电磁透射率、反射率计算方法和厚度远低于网格尺寸的薄膜等效处理时域有限差分（FDTD）算法,设计了一种透明导电镀膜的介质屏蔽结构,建立复杂结构与电磁参数的真实三维飞机-飞行员模型,开展了电磁防护分析。仿真结果表明：采用电场幅度最值衰减和防护极限评估防护效果具有良好的工程适用性,且该屏蔽结构在一定载频范围内辐射防护效能好,防护极限高。     

FMM算法用于二维复杂散射体的RCS计算

利用快速多极子算法(FMM)计算任意形状二维电大尺寸导体加介质体目标的电磁散射，介质体为镶嵌在电大尺寸金属体上的有耗介质。建立金属一介质体的混合积分方程，用共轭梯度法和场量叠代的方法计算散射场，在叠代过程中用快速多极子方法，大大降低计算时间和减小内存要求。数据结果表明该方法的准确和高效。     

改进的IPO与FEM混合法分析复杂电大腔体电磁散射

对传统的迭代物理光学法(IPO)进行了改进,使之适合于分析具有非完纯导电边界的电磁问题,并与矢量有限元方法(FEM)相结合,对内壁涂敷介质的具有复杂终端结构的电大尺寸腔体的电磁散射特性进行分析.通过Fresnel反射系数,利用IPO方法处理腔体内壁比较平滑的介质涂敷区域,在结构复杂的终端区域,利用FEM进行分析.利用交界面上场强连续条件实现两个区域之间的电磁耦合.通过迭代,计算出腔体内部稳定的电磁场分布,进而获得整个腔体的散射特性.由于在介质涂敷附近区域避免了FEM处理过程,从而可以节省大量计算时间和内存消耗.     

Aperture excitation of electrically large, lossy cavities

We present a theory based on power balance for aperture excitation of electrically large, lossy cavities. The theory yields expressions for shielding effectiveness, cavity Q, and cavity time constant. In shielding effectiveness calculations, the incident field can be either a single plane wave or a uniformly random field to model reverberation chamber or random field illumination. The Q theory includes wall loss, absorption by lossy objects within the cavity, aperture leakage, and power received by antennas within the cavity. Extensive measurements of shielding effectiveness, cavity Q, and cavity time constant were made on a rectangular cavity, and good agreement with theory was obtained for frequencies from 1 to 18 GHz     

Scattering from 3-D cavities with a plug and play numerical schemecombining IE, PDE, and modal techniques

In this paper, we present a multidomain and multi-method coupling scheme called FACTOPO, based on generalized scattering matrix computations on three-dimensional (3-D) subdomains. The global target Ω is split in N_V subdomains (V_i)(i=1, N_V), separated by N_I fictitious surfaces (Γ _j)(j=1,N_I). We use a modal representation of the tangent fields on the interfaces. In each domain, the generalized scattering matrix S_i is computed with different methods such as the 3-D finite-element method (FEM) or the electric field integral equation (EFIE). This coupling scheme leads to an important reduction in computational resources, especially for cavities with one dimension much larger than the other two. The advantages of this formulation for parametric studies is illustrated by two cases: computing the RCS of an air-intake terminated with a flat PEC or a fan (CHANNEL) and of an antenna structure coupled to an electronic feed with a varying parameter (DENEB). Numerical as well as experimental results are presented     

FMM用于快速计算电大腔体的RCS

利用迭代物理光学法(IPO)计算一般电大尺寸腔体的电磁散射特性,在迭代过程中用快速多极子方法(FMM)加速计算.在雅可比最小残差法(JMRES)的积分运算中引入FMM并与共扼梯度法(CG)的计算效率进行了比较.采用结构化分组,利用转移因子的平移不变性对计算和存储进行了优化.计算结果表明这些加速方法是有效的并能极大地提高计算效率.     

Stability analysis for laser diodes with short external cavities

Results of a numerical analysis of the stability of external cavity lasers with short external cavities are presented. If the external cavity is shorter than about 5 mm (air equivalent), the laser remains stable for any feedback from that cavity without any coherence collapse. The results can be considered also as guidelines for the design of laser diodes with integrated passive cavities.<>     

半空间电大均匀介质目标散射分析方法

研究了半空间电大尺寸均匀介质目标散射的高频求解方法.考虑电大均匀介质目标散射特性,将半空间并矢格林函数引入物理光学近似中,结合图形电磁学(GRECO)和射线追踪方法,分别对半空间复杂目标的消隐和多重散射进行考虑,快速有效地计算了半空间电大均匀介质目标的雷达散射截面(RCS),数值结果证明了该方法的准确性.     

Scattering matrix analysis of a triangular ring laser

A method of analysis for ring waveguide lasers is presented. This method is based on the use of the scattering matrix formulation to represent the waveguide junctions. An extension of previous work is made so that any number of junctions may be serially connected. The method is then applied to a three-junction triangular ring laser and various operating characteristics are calculated, in particular the longitudinal mode spacing and the power ratio of the counterpropagating waves of the laser. It is found that this ratio is much more sensitive to a difference in forward coupling than to backward coupling, but that a difference in either will enhance unidirectional operation of the device. Comparison to experimental data is made where possible     

电大尺寸开口腔体电磁散射的子结构法研究

将子结构法与矢量有限元法相结合对无限大接地的三维开口腔体的电磁散射特性进行分析.将原尺寸较大的腔体分解成若干个不重叠的子腔体,在各子腔体内应用矢量有限元法进行分析,在原腔体开口面应用边界积分方程描述.通过求解容量矩阵获得子腔体之间连接边界上的场值,可以快速获得腔体开口面上的场值,极大地减少了存储量和计算量,易于对电大尺寸腔体的电磁散射问题进行分析.数值算例验证了该方法的准确性和高效性.     

Simple analysis of a diode laser having two orthogonal Fabry-Perot cavities

Simple rate equations have been used to analyze the steady-state behavior of a double-cavity diode laser with two separately driven active regions, one of which is shared by both cavities. It is shown that the output from one cavity depends with an inverse linear relationship on the output of the other, in agreement with the experimental results of Kosonocky, Cornely, and Marlowe. The stability of the steady-state solutions has been studied by a perturbation method, yielding a value for the response time of 0.2 ns. It is found that unstable situations exist for certain values of some of the parameters, indicating the possibility of an oscillatory output. A similar method of analysis has been used to obtain the response time of a normal single-cavity laser. For abrupt changes in the drive current when the laser is already emitting, the calculated response time is in good agreement with the experimental values obtained by Basov et al.     

介质涂覆电大复杂腔体散射的快速求解

利用腔体涂覆层是薄层损耗介质的情况,引入阻抗边界条件求解腔体的介质涂覆区域.详细推导了快速多极子方法结合迭代物理光学法和阻抗边界条件的混合计算公式.在此基础上利用前后向迭代方法加速收敛.计算结果表明该方法比IPO FMM方法有效地减少了迭代次数,能够对腔体涂覆材料的电磁参数、腔体涂覆部位进行优化设计,对开口腔体的RCS减缩提供理论参考.     

Fast coupled-integral-equations-based analysis of azimuthally corrugated cavities

An approach is developed for fast analysis of a wide class of azimuthally corrugated coaxial and circular structures employed in various microwave devices. In line with it, the eigenvalues of a geometrical parameter (GP) are calculated instead of the eigenfrequencies resulting in substantial acceleration of the analysis and improvement of the design efficiency. To formulate the eigenvalue problem, the accelerated coupled-integral-equations technique and the Galerkin method with weighted Gegenbauer polynomials as basis functions are applied.     

A hybrid SBR/MoM technique for analysis of scattering from smallprotrusions on a large conducting body

A hybrid technique combining the shooting-and-bouncing-ray (SBR) method and the method-of-moments (MoM) is presented for analyzing scattering by large conducting bodies having small protrusions. In this technique, the MoM with an approximate Green's function is used to characterize the small protrusions, yielding an admittance matrix, which, when multiplied with the incident field on the protrusions, yields the currents induced on the protrusions. The incident field in the presence of the large bodies is calculated using the SBR method. The field radiated by the currents on the protrusions is also calculated using the SBR method with the aid of reciprocity. Furthermore, an iterative approach is developed, which can reduce the error introduced by the use of the approximate Green's function, Numerical results are given to demonstrate the accuracy and capability of the hybrid technique     

Comment on "Scattering by a bi-isotropic body" [and reply]

The author comments on a paper by Monzon (IEEE Trans. Antennas Propagat., vol.43, p.1288-96, Nov. 1995). The author comments that Monzon gave no indication as to whether the nonreciprocal variety of bi-anisotropic media can or do exist. The present comment notes that there is no reason to suggest that these can or do exist. A reply is presented by Monzon where he feels that the situation regarding these materials is not yet settled.     

YAG激光器中不同聚光腔的实验比较及分析

在脉冲YAG激光器中，在保持激光棒，泵浦氙灯，谐振腔不变的情况下，实验研究了不同聚光腔对该器件振荡效率的影响，并作了相应的分析。实验表明，精心制作的用MgO粉压制的漫反射聚光腔有不低于单椭园柱聚光腔的效率，并且有制作简便，成本低，照明较均匀，性能稳定，灯和激光棒能方便地同时冷动等优点。