EM programmer's notebook-benchmark radar targets for the validationof computational electromagnetics programs

Low- and high-frequency measurements are presented of five differently shaped targets: the NASA almond, ogive, double ogive, cone-sphere, and cone-sphere with gap. These were measured from 700 MHz to 16 GHz. The metallic targets are made of aluminum, and were cut by a numerically controlled mill to maintain the surface precision. Except for the almond target, all the targets were made in two parts and joined by sleeves and screws. The measurements are computational electromagnetics (CEM) validation measurements for the Electromagnetic Code Consortium (EMCC)     

Expansion of existing EM workbench for multiple computational electromagnetics codes

An "EM workbench" is described. It has a modular, code-independent architecture and a common design environment. The technique for integrating new EM codes is demonstrated with a method-of-moments code specialized for circularly symmetric feed horns, and with a new hybrid DFT-MoM (discrete Fourier transform - method of moments) code for finite-boundary planar phased arrays. The use of a common design environment for all codes takes advantage of common infrastructure and utility software, and minimizes the learning-curve penalty for using a new EM code capability.     

Low-frequency computational electromagnetics for antenna analysis

An overview of computational methods for modeling the low-frequency electromagnetic characteristics of antennas is given. Presented first is a brief analytical background that forms the basis for numerically solving low-frequency antenna problems using the method of moments. Next discussed are extensions to modeling perfectly conducting objects in free space, followed by a consideration of some computational issues that affect model accuracy, efficiency, and utility. A variety of representative applications is given to illustrate various aspects of modeling and capabilities that are currently available. A fairly extensive bibliography is included     

Integer lattice gas automata for computational electromagnetics

Integer lattice gas automata (ILGA) are combined with the transmission-line matrix (TLM) method to yield a new electromagnetic-field computation algorithm using very low-precision integer variables. Lattice gas automata can be evaluated using look-up tables on special-purpose hardware and do not require floating-point arithmetic. In this paper, we present a TLM motivated ILGA with emphasis placed on algorithms that demonstrate minimal dissipation     

Programming video cards for computational electromagnetics applications

Recently, programming tools have become available to researchers and scientists that allow the use of video cards for general-purpose calculations in computational electromagnetics applications. Over the past few years, developments in the field of graphic processing units (GPUs) for video cards have vastly outpaced their general central processing unit (CPU) counterparts. As specifically applied to vector mathematic operations, the newest generation GPUs can generally outperform current CPU architecture by a wide margin. With the addition of large onboard memory units with significantly higher memory bandwidth than those found in the main system, graphic cards can be utilized as a highly efficient vector mathematic coprocessor. In the past, this power has been harnessed by writing low-level assembly code for the video cards. Recently, new tools have become available to make programming possible in high-level languages. By formulating proper procedures to realize general vector computations on the GPU, it will be possible to increase the processing power available by at least an order of magnitude compared to the current generation of CPUs.     

A selective survey of computational electromagnetics

Some of the tools used in computational electromagnetics are placed into perspective with respect to the different kinds of approaches that may be used and their computer-resource requirements. Particular attention is paid to numerical models based on integral and differential equations. After a brief background discussion, some of the analytical and numerical issues involved in developing a computer model are reviewed. Some practical considerations are included from the viewpoint of computer-resource requirements, followed by a discussion of some ways by which computer time might be reduced. The presentation concludes with a brief examination of validation and error checking. The emphasis throughout is on review and summarization rather than detailed exposition     

High-order Runge-Kutta multiresolution time-domain methods for computational electromagnetics

In this paper we introduce a class of Runge-Kutta multiresolution time-domain (RK-MRTD) methods for problems of electromagnetic wave propagation that can attain an arbitrarily high order of convergence in both space and time. The methods capitalize on the high-order nature of spatial multiresolution approximations by incorporating time integrators with convergence properties that are commensurate with these. More precisely, the classical MRTD approach is adapted here to incorporate mth-order m-stage low-storage Runge-Kutta methods for the time integration. As we show, if compactly supported wavelets of order N are used (e.g., the Daubechies D/sub N/ functions) and m=N, then the RK-MRTD methods deliver solutions that converge with this overall order; a variety of examples illustrate these properties. Moreover, we further show that the resulting algorithms are well suited to parallel implementations, as we present results that demonstrate their near-optimal scaling.     

Hierarchical parallelisation strategy for multilevel fast multipole algorithm in computational electromagnetics

A hierarchical parallelisation of the multilevel fast multipole algorithm (MLFMA) for the efficient solution of large-scale problems in computational electromagnetics is presented. The tree structure of MLFMA is distributed among the processors by partitioning both the clusters and the samples of the fields appropriately for each level. The parallelisation efficiency is significantly improved compared to previous approaches, where only the clusters or only the fields are partitioned in a level.     

雷达目标角闪烁特性仿真分析

目标角闪烁偏差是限制跟踪雷达,尤其是近距离跟踪雷达的角跟踪精度的主要因素。在实际跟踪和制导中,如 果对目标回波信号的角闪烁偏差处理不当可能加大雷达跟踪目标的误差,甚至丢失目标。因此对角闪烁偏差的研究将有 助于提高跟踪目标的准确率。本文首先对目标进行几何建模,得到模型的三角面元信息;然后基于面元信息,应用等效 电磁流方法（MEC）计算目标的电磁回波场;再利用相位梯度方法完成目标的角闪烁计算,从而提高了计算精度. 最后, 选用立方体目标进行角闪烁校模,证明了此方法的可行性。     

On the design of numerical methods [computational electromagnetics]

Many terms and ideas used in numerical methods have their origin in analytical mathematics. Despite the well-known discrepancies between number spaces of computers and those of mathematics, the consequences of applying mathematical theorems to numerical methods and the importance of physical reasoning are often underestimated. It is demonstrated that terms known from analytic considerations and goals like orthogonal basis functions and small condition numbers of matrices can be misleading, and can prevent engineers from designing useful codes for computational electromagnetics and similar tasks. Introducing a priori knowledge in numerical codes requires open structures, and often leads to ill-conditioned matrices. Thus, it is important to develop and apply methods for handling matrices such as the generalized point matching used in the multiple multipole (MMP) code instead of the projection technique used in many method of moments (MoM) codes     

Using object-oriented and literate-programming techniques for the development of a computational electromagnetics library

Code maintenance is perhaps the most time-consuming problem in developing source code for various purposes. The increased complexity of computational-electromagnetics (CEM) simulation software makes this task even more difficult and tedious. The current paper proposes a sophisticated approach for a significant performance improvement in CEM code-maintenance tasks, with the fusion of object-oriented and literate-programming techniques. A case study concerning the development of a CEM library is thoroughly analyzed and presented. Various aspects of computational efficiency have been examined in order to estimate the costs of developing object-oriented CEM programs. The aim of the analysis is to stress the advantages of the above-mentioned techniques, and to provide useful guidelines for effective implementation of CEM programs with reusable, extensible, self-documented source code.     

Nonsinusoidal radar signal design for stealth targets

The detection of stealth point targets challenges the design of conventional radars using sinusoidal carriers since the objective of stealth technology is to reduce the radar cross section (RCS) of targets to a level where the radar receiver cannot detect the target. While there are a number of techniques employing different technologies to reduce the RCS of targets, shaping and coating the target with absorbing material are the most useful ones. The analysis and design of nonsinusoidal radar signals is based on modeling stealth point targets by a two-layer structure consisting of a metal surface covered with a coat of absorbing material. The design is presented for two classes of signals: uncoded signals and pulse compression signals using Barker codes. The relationship between target response, absorbing material time delay, time variation of transmitted pulses and coding features are determined and analyzed. While sliding correlators are used for detection and selection of various target responses, their output autocorrelation functions are determined analytically in terms of transmitted signal autocorrelation functions. Thumbtack range-velocity resolution functions are obtained for transmitted signal characters with a single pulse and characters with coded waveforms, for different pulse duration. It is shown that the range resolution can be improved by the proper choice of the transmitted signal duration relative to absorbing material time delay. Thumbtack range-velocity resolution functions similar to those of conventional point targets can also be realized     

计算电磁学中的时域有限元方法稳定性分析

对计算电磁学中的时域有限元方法(TDFEM)迭代稳定性问题进行了分析,讨论了中心差分、前向差分、后向差分和Newmark差分四种不同时间步长离散格式的迭代收敛情况,及其对数值结果精度的影响,并作了对比.在此基础上,研究了Newmark方法中参数β的确定和时间步长的选择.数值结果表明:采用Newmark方法,TDFEM可以在较大时间步长和较少迭代步数情况下将数值误差控制在1%左右,从而验证了时域有限元方法中Newmark技术的精确性和高效性.     

A hybrid computational electromagnetics formulation for Simulation of antennas coupled to lossy and dielectric volumes

A heterogeneous hybrid computational electromagnetics method is presented, which enables different parts of an antenna simulation problem to be treated by different methods, thus enabling the most appropriate method to be used for each part. The method uses a standard frequency-domain moment-method program and a finite-difference time-domain program to compute the fields in two regions. The two regions are interfaced by surfaces on which effective sources are defined by application of the Equivalence Principle. An extension to this permits conduction currents to cross the boundary between the different computational domains. Several validation cases are examined and the results compared with available data. The method is particularly suitable for simulation of the behavior of an antenna that is partially buried, or closely coupled with lossy dielectric volumes such as soil, building structures or the human body.     

OFDM MIMO radar waveform design for targets identification

In order to obtain better target identification performance, an efficient waveform design method with high range resolution and low sidelobe level for orthogonal frequency division multiplexing (OFDM) multiple-input multiple-output (MIMO) radar is proposed in this paper. First, the wideband CP-based OFDM signal is transmitted on each antenna to guarantee large bandwidth and high range resolution. Next, a complex orthogonal design (COD) is utilized to achieve code domain orthogonality among antennas, so that the spatial diversity can be obtained in MIMO radar, and only the range sidelobe on the first antenna needs suppressing. Furthermore, sidelobe suppression is expressed as an optimization problem. The integrated sidelobe level (ISL) is adopted to construct the objective function, which is solved using the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm. The numerical results demonstrate the superiority in performance (high resolution, strict orthogonality, and low sidelobe level) of the proposed method compared to existing algorithms.     

高频地波雷达海面舰船RCS预估

为了有效预估高频雷达海面目标的短波散射特性,采用两媒质半宽间FDTD方法对海面舰船目标电磁建模.通过对有限长贴地介质圆柱进行电磁建模,证明了该方法计算结果的准确性.最后,以海面某海监船为研究对象,分析其电磁散射情况,并将计算结果与实验观测结果进行了对比,结果表明:两者吻合良好.     

Image simulation of geometric targets for spaceborne syntheticaperture radar

A technique of synthetic aperture radar (SAR) image simulation is proposed. The method is based upon embedding of simulated man-made targets in a real background taken among the scenes captured by a spaceborne SAR. Scenes observed at 30 and 3 cm wavelength are used and the target dimensions are large enough with respect to the wavelength in order to compute the radar cross section from high frequency approximation techniques. Once the simulated image of the target is computed, the embedding process is performed bearing in mind the problems involved with this particular process. Although the simulation possibilities are restricted due to the simplifying assumptions, the results are sufficiently realistic to allow for the study of the detectability of a particular man-made target in a SAR environment     

A characterization of subsurface radar targets

The capability of subsurface target identification at shallow depths has been demonstrated using an electromagnetic video or base-band pulse radar. Real radar measurements were collected for five targets at a depth of 5 cm (2 in) in various ground conditions. These measurements were processed for target characterization and identification. Identification performance based on a single radar observation was evalualted. The identification process requires only simple algebraic operations and thus offers the potential of real-time on-location identification of subsurface targets.     

Multiresolution detection of coherent radar targets

We develop and investigate several novel multiresolution algorithms for detecting coherent radar targets embedded in clutter. These multiresolution detectors exploit the fact that prominent target scatterers interfere in a characteristic manner as resolution is changed, while multiresolution clutter signatures are random. We show, both on simulated and collected synthetic aperture radar data, that these multiresolution algorithms yield significant detection improvements over single-pixel, single-resolution constant false alarm rate (CFAR) methods that use only the finest available resolution.     

Detection and discrimination of radar targets

A new method for detection and discrimination of radar targets is described. The basis for this method is that the gross structure of a radar target can be identified from scattered fields of the target at harmonic radar frequencies located just in the low resonance region. This is in sharp contrast to many target signature schemes that operate at much higher frequencies and observe many of the details of the target in lieu of its gross features. Multiple frequency radar scattering data and the complex natural resonant frequencies of radar targets are integrated into a predictor-correlator processor. The method is illustrated using as target models both classical shapes and thin-wire configurations of simple geometry. Integral equation programs are utilized to calculate multiple frequency backscatter data for the wire geometries and to deduce the complex natural resonant frequencies of the wire structures. Discrete multiple frequency radar scattering data spanning a particular spectral range are shown to be desirable for optimum capability but discrimination and detection can be achieved using just two near-conventional radars, even if the radars are located at different sites and hence view the target from different aspects.