Extended spectral domain approach for analysis of lossy cylindrical dielectric resonators

The spectral domain approach is extended for evaluating both the resonant frequency and Q factor of a lossy cylindrical dielectric resonator operating in TE/sub 0/ modes, taking into account the effects of conducting enclosure and supporting substrate. On the basis of the equivalence principle, the circular electric currents are introduced to simulate the fields inside and outside the cylindrical dielectric sample, which separates the original problems into two auxiliary structures with radially homogeneous multilayered dielectrics. Using the spectral immittance method in conjunction with the point-matching method, the characteristic equations are derived. The present technique has no need to determine the time-consuming, complex higher-order modes. Some typical examples are computed. The numerical results agree well with experimental data available in the literature.<>     

Analysis of electromagnetic scattering from dielectric cylinders using a multifilament current model

A moment solution is presented for the problem of transverse magnetic (TM) scattering from homogeneous dielectric cylinders. The moment solution uses fictitious filamentary currents to simulate both the field scattered by the cylinder and the field inside the cylinder and in turn point-matches the continuity conditions for the tangential components of the electric and magnetic fields across the cylinder surface. The procedure is simple to execute and is general in that cylinders of arbitrary shape and complex permittivity can be handled effectively. Metallic cylinders are treated as reduced cases of the general procedure. Results are given and compared with available analytic solutions, which demonstrate the very good performance of the procedure.     

Analysis of electromagnetic scattering from dielectrically coatedconducting cylinders using a multifilament current model

A method of moments solution is presented for the problem of transverse magnetic scattering from dielectrically coated conducting cylinders. The solution uses fictitious filamentary electric sources of yet unknown currents to simulate both the field scattered by the cylinder and the field inside the dielectric coating. The simulated fields obey the boundary conditions, namely, the continuity of the tangential components of the electric and magnetic fields across the air-dielectric interface and the vanishing of the tangential component of the electric field at the perfect conductor, at selected sets of points on these respective surfaces. The result is a matrix equation that is readily solved for the unknown current. The currents can be used to determine approximate values for the fields and field-related parameters of interest. The procedure is simple to implement and is general in that cylinders of smooth but otherwise arbitrary shape and coating of arbitrary complex permittivity can be handled. Illustrative examples are considered and compared with available data, demonstrating the efficiency of the solution     

Shielding effectiveness and statistical analysis of cylindrical scale fuselage model

In this paper, the shielding effectiveness of a cylindrical scaled fuselage model is examined. Measurements of the penetrated field, are performed as a function of frequency. The penetrated field is further statistically analyzed and its distribution is investigated. For the purposes of this investigation, different probability models are introduced while their ability is tested to match the measured data distribution.     

有耗平面和三维目标复合散射的FDTD分析

采用FDTD方法计算了有耗地面与三维目标的复合散射,对吸收边界条件,连接边界条件和近远场变换作了细致讨论.吸收边界使用了广义PML吸收层,它对电磁波有较好的吸收效果.连接边界处则利用解析入射波和三波迭加技术,上半平面用入射波和反射波、下半平面用透射波作为对目标的外加场进行计算.得到近场数据后,为避免出现复杂的Sommerfeld积分,用互易原理简化了外推过程.FDTD算法与矩量法和快速多层多极子相比,具有节省内存,计算时间短等优点.通过地上物体和地下物体的计算验证了FDTD方法的精确性,讨论了散射体离地高度对后向RCS的影响.     

A surface integral equation approach to the scattering andabsorption of doubly periodic lossy structures

The scattering and absorption of a doubly periodic array of absorbers, either placed in free space, backed by a perfect conductor or by a half-infinite space with the same material properties as the elements forming the array, is analyzed with a surface integral equation approach (SIE). The use of a suitable periodic Green's function as kernel of the SIE reduces the formulation of the problem to a single absorber. A set of equivalent electric and magnetic currents on the surface of the absorber is discretised using Glisson functions and the SIE is solved with Galerkin's method. The validity and flexibility of the SIE approach is exemplified by comparing numerical results with measurement data for a family of commercially available absorbers     

Development and validation of altimeter wind speed algorithms usingan extended collocated Buoy/Topex dataset

The development and validation of altimeter wind speed algorithms is investigated following the collation of the largest dataset to-date of coincident altimeter/buoy open ocean measurements. Nonlinear relationships between buoy wind and Topex backscatter are fitted to the 4500 points dataset using least-squares (LSQ). The addition of altimeter significant wave height (SWH) information causes a small but significant reduction of about 10% in root-mean-square (rms) error. The new LSQ algorithms yield significant improvement of the global wind speed bias and rms error compared to earlier models, but describe the wind to backscatter relationship poorly at extreme wind speeds. Best results are obtained with the Gourrion et al. (2000) model, improving on the Witter and Chelton (WC91) (1991) model used operationally. A residual dependence on sea state persists in all wind algorithms, which underestimate winds in young sea conditions on average by 1-1.5 m/s. A case study confirms that ordinary LSQ attribute excessive weight to the peak of the wind speed histogram and yield algorithms with poor performance at extreme winds. Measurement errors are shown to greatly influence the fitted models performance, as accounting for normally distributed errors in both altimeter and buoy measurements with orthogonal distance regressions (ODRs) yields significant improvements     

Resonant frequencies and quality factors in lossy NRD cylindrical resonators

In this paper the fundamental effects of losses on resonant parameters (frequencies and quality factors) are analyzed for circular-cylindrical dielectric resonators inserted between metal plates, in the configuration also called NRD (Non-Radiative Dielectric). Power dissipations are considered both in the dielectric and in the conductors. Complex resonant frequencies and closed-form expressions for the relevant quality factors are derived rigorously for arbitrary resonant modes, even without circular symmetry. Numerical results are presented and discussed, making also use of experimental data obtained by means of a suitable NRD set-up. The present analysis accurately provides the basic information for a more realistic design of up-to-date millimeter-wave frequency-selective devices in NRD circuitry.     

MMW scattering by rough lossy dielectric cylinders and tree trunks

The millimeter-wave (MMW) radar backscatter response of a rough, lossy, dielectric cylinder is examined both analytically and experimentally. Models for both the coherent and incoherent components of the scattered field are developed based on the geometric-optics approximation. The accuracy of the analytical models and their applicability in predicting the backscatter response of tree trunks are determined experimentally by measuring the radar backscatter at 95 GHz from a rough conducting cylinder and from a section of a tree trunk. In both cases, very good agreement was achieved between the model predictions and the measurements     

Shielding of wire segments and loops in electric circuits byspherical shells

The susceptibility of an electric circuit to electromagnetic radiation incident on it is analyzed by the application of Lorentz's reciprocity relation. An equivalent Thevenin or Norton representation of the circuit serves to determine the induced signals quantitatively. The effect of a (multilayered) spherical shield on the performance of elementary parts of the circuit, namely, a short wire segment and a loop placed at the center of the shield, is investigated. The corresponding shielding performance is expressed as the reduction of the induced source strength in the equivalent networks. Numerical results are presented in a frequency range that includes the occurrence of internal resonances in the shielding structure     

Receiving and scattering characteristics of an imaged monopolebeneath a lossy sheet

An analytical treatment of the radiation, scattering, and receiving properties of an imaged monopole in trilayered media with a perfectly conducting ground plane, a dielectric substrate, an electrically or magnetically lossy sheet as superstrate, and a homogeneous cover region is carried out. It is shown that while the power received by the monopole antenna is reduced by the presence of the lossy sheet, the scattered field is more greatly reduced, in agreement with observed behavior. Comparison with experimental and previously published numerical results validates the analysis     

Wave scattering by a prism made of a lossy metamaterial

The results of rigorous calculation of the scattering pattern of a Gaussian beam incident onto a finite prism made of a metamaterial are presented for different values of the refractive index n _r < 0 and loss factor ν of the medium. It is shown that geometric optics can correctly predict the tilt of the scattering-pattern maximum, while consideration for the medium’s loss factor 0.001 ≤ |ν| ≤ 0.1 affects the amplitudes of the transmitted and reflected fields.     

Integral equation modeling of the scattering and absorption ofmultilayered doubly-periodic lossy structures

Previously, the scattering and absorption of a doubly-periodic array of pyramidal absorbers were analyzed using a surface integral equation (SIE) approach. This method is now extended to multilayered absorbers with arbitrarily shaped surfaces between the layers. The developed method is verified on planar stratified absorbers, on wedge absorbers, and rectangular absorbers showing the capability of the method to handle such structures as well. It is also shown that convergence depends critically on the discretization of the equivalent electric and magnetic current     

Relationship between radiation pattern correlation and scattering matrix of lossless and lossy antennas

A relationship between the scattering parameters of a set of antennas and the correlation between the signals received by them is derived. This relationship is valid for an arbitrary number of ports and antenna elements under the assumption that the environment is completely uniform with respect to incidence angles and polarisation state.     

Finite element analysis of electromagnetic scattering from periodic cylindrical structures at oblique incidence

A hybrid technique which combines the finite element method (FEM) and an expansion of the field in terms of Floquet modes is presented for the analysis of the scattering from, and the transmission through, penetrable periodic cylindrical structures, at skew incidence. The method is very flexible and allows the analysis of practical cylindrical configurations with arbitrary cross-section and material properties.<>     

An efficient approach for evaluating Sommerfeld integrals encountered in the problem of a current element radiating over lossy ground

Efficient numerical evaluation of the Sommerfeld integrals, arising from the problem of a current element radiating over a lossy half-space, is considered. An integration technique based on the method of steepest descent is investigated. The details for computing possible pole and branch cut contributions resulting from the deformation of the path of integration are presented. A computer program for evaluating Sommerfeld integrals is developed on the analysis presented. Numerical results and estimates of computational efficiency of the method are given and a comparison with other available works in the literature is included.     

基于FGMRES-PBTG算法的介质粗糙面散射特性的模拟

针对具有大介电常数介质粗糙面的电磁散射问题,提出了灵活的广义最小余量法(FGMRES)和基于物理意义的双网格法(PBTG)的混合算法,并对介质粗糙面的电磁散射系数和发射率进行了仿真.在PBTG算法的基础上,应用了FGMRES迭代算法求解矩阵方程.通过PBTG算法加速矩阵向量积和FGMRES算法加快迭代收敛速度,达到减少计算量和加快计算速度的目的.通过计算实例可知,FGMRES相对其他迭代法具有很好的收敛性,耗时较少,在满足精度要求的前提下,较其他迭代法明显加快了计算速度,并有效地模拟了介质粗糙面的电磁散射特性.     

Rigorous analysis of radiation properties of lossy patch resonatorson complex anisotropic media and lossy ground metallization

An extended spectral-domain immittance approach for the rigorous analysis of resonant frequencies and radiation characteristics of microstrip resonators is presented. The dyadic Green's function in the spectral domain is modified to include a complex anisotropic substrate with both permeability and permittivity tensors, lossy ground metallization, and a lossy conducting patch of conventional or superconducting material. Closed-form expressions for the transverse propagation constants and related immittances of TE and TM waves in the spectral domain lead to a CPU-time efficient algorithm that is operational on standard workstations. Numerical results show how the radiation characteristics are affected by losses as well as uniaxial and biaxial anisotropies