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In this communication, we combine the facet-based bidirectional reflection distribution function (BRDF) and four-path model (FPM) to establish the attribute scattering center (ASC) model for composite scattering simulations. This hybrid method is beneficial for simulating scattering echoes of large composite scenes with high efficiency. The model consists of three parts: the ASC model for the target, the BRDF-ASC model for the rough dielectric background, and the FPM-BRDF-ASC model for the coupling scattering between the target and the background. Two simple composite scenes and two large composite scenes are taken as examples to verify the accuracy and feasibility of the proposed model. The validation results show that the radar cross sections (RCSs) of the proposed hybrid method are consistent with those of the multilevel fast multipole algorithm (MLFMA) with higher simulation efficiency. In addition, the ghosting image caused by the multipath effect can be well displayed in the simulated synthetic aperture radar (SAR) images. [ABSTRACT FROM AUTHOR]

Radar imaging of typical planet landforms can be used for planetary exploration such as landform recognition and geometry measurement. This communication realizes high-resolution imaging simulations of typical planetary landforms, such as craters, hills, and volcanoes, by using parametric scattering center (SC) models. Based on the geometric models of these typical landforms, parametric SC models are constructed from scattered solutions of the physical optics (POs) method. Because the SC models take geometric parameters as model parameters, these models can simulate the scattered waves of landforms of different sizes. These SC models are validated by the PO results. In addition, the landform types can be recognized and their geometrical parameters are further extracted by SC model matching. The extracted geometric parameters show good agreement with real landforms, demonstrating that the SC models of typical planetary landforms have potential applications in planetary geomorphologic exploration. [ABSTRACT FROM AUTHOR]

A conducting deep cavity is an essentially geometric structure, e.g., the inlet duct and the tail nozzle, of air vehicles and is a dominant scattering source of radar echoes. The scattering centers (SCs) induced by multiple reflections inside deep cavities are different from general SCs. Few references have studied the SC model for deep cavities. Therefore, a concise SC model is presented in this letter. In this model, an analytical expression for the projection distances of SCs along the line-of-sight (LOS) in deep cavities is derived by using the ray- tracing method. Rectangular cavities, cylindrical cavities, and a cavity composed of two cylindrical structures are investigated in this letter. The presented SC models are validated by a comparison between the radar images simulated by the model and those computed by a full-wave numerical method. [ABSTRACT FROM AUTHOR]

The combined-field integral equation (CFIE) usually is less accurate than the electric-field integral equation (EFIE), especially for objects with sharp edges and corners. In this work, we propose a simple but accuracy enhanced CFIE (AE-CFIE) strategy for computing scattering from perfect electric conductor (PEC) objects. AE-CFIE directly replaces the original CFIE on the sharp edges with EFIE. Using the dihedral angle of the meshes to describe the sharpness of the geometric structure, the hybrid criterion of EFIE/CFIE has been studied in detail. This strategy can be implemented conveniently under exiting basis functions and only a few lines of code need to be changed. Due to the inclusion of EFIE, AE-CFIE may sacrifice the convergence speed compared with CFIE. Therefore, we also investigate the performance of AE-CFIE with or without the preconditioner. Numerical examples show the performance of AE-CFIE, and a comprehensively study is made to demonstrate its validity, reliability, and stability. [ABSTRACT FROM AUTHOR]

Traveling waves can be supported by long, smooth surfaces under horizontal polarization, such as the wings or bodies of aircraft. A 3-D scattering center (SC) model for traveling waves is proposed in this work. The equivalent location of the SC and the dependence function of scattering amplitude on aspect angles is derived based on traveling wave antenna theory and modified according to real scattering characteristics. Chamber-measured data and full-wave numerical results of a series of geometries are presented to verify the validity of this model in imaging simulation. We find that the equivalent position of this SC is located along a circular arc. In consideration of its polarization characteristics and inverse synthetic aperture radar (ISAR) image signatures, the proposed SC model is promising for used in the model-based automatic target recognition (ATR) to distinguish traveling waves from other scattering components. [ABSTRACT FROM AUTHOR]

We present in this paper an efficient parallelization approach of the finite element domain decomposition method (FEM‐DDM) for solving large‐scale 3D scattering problems with over ten billion unknowns. In this parallel FEM‐DDM, the whole solution domain is decomposed in a two‐level hierarchical way to minimize the inter process communication. A communication‐avoided block diagonal symmetric Gauss‐Seidel (BD‐SGS) preconditioner is specially designed to accelerate the iterative solution of the interface problem from FEM‐DDM and reduce the CPU time, as well as the peak memory. Besides, a communication strategy is carefully designed to make computation and communication overlapped via nonblocking sending and receiving to further improve the parallel scalability. Numerical examples are presented to demonstrate the accuracy, scalability, and capability of the proposed parallel FEM‐DDM algorithm. The solutions of scattering by a practical aircraft model with a three‐layer antenna radome on its nose section is presented, which are discretized with more than ten billion unknowns. To the best of our knowledge, this is the largest number of unknowns solved by parallel FEM‐DDM in computational electromagnetics to date, for this type of simulation. [ABSTRACT FROM AUTHOR]

The scattering center (SC) model provides a concise, explicit description of the object electromagnetic characteristics, significantly improves the efficiency of radar signal simulations, and plays an important role in model-based automatic target recognition. The existing models are mainly developed for conducting objects, and few are developed for dielectric ones. The SC models of dielectric objects are essentially different from those of their conducting counterparts due to the different scattering mechanisms. In this article, the backscattering mechanisms of canonical dielectric structures are studied, and their corresponding SC models are proposed. More importantly, the parametric SC models of the composite objects of canonical structures are first presented. These SC models are validated by comparing the radar cross section (RCS), the time–frequency representation (TFR), and the high-resolution range profile (HRRP) from the SC model with the results of the full-wave numerical method. [ABSTRACT FROM AUTHOR]

The discontinuous Galerkin (DG) method for homogeneous bodies has been studied and shown to be an efficient tool for multiscale homogeneous bodies. However, the slow convergence of DG with the block diagonal preconditioner (BDP) is still observed in solving high contrast homogeneous bodies. An efficient preconditioning approach is designed for the DG method in this communication by using the sparsing approach on the near-field matrix of the whole region. The iteration convergence speed of the DG method is improved while the computing resources for constructing the preconditioner are effectively reduced. Numerical experiments demonstrate the capability of the presented DG method for multiscale homogeneous bodies, especially for those with a high dielectric constant. [ABSTRACT FROM AUTHOR]

In this paper, we present a flexible and efficient ternary parallelization approach for the multilevel fast multipole algorithm (MLFMA) for the solution of extremely large 3-D scattering problems with over 10 billion unknowns. In the ternary parallelization approach, a binary clustering tree of all the message passing interface (MPI) processes is built first. Then, the MLFMA tree is categorized into plane wave partitioning, hierarchical-structure partitioning, and box partitioning (BP) levels via a top–down approach to match the process clustering tree. Compared with the bottom–up approach, interprocess communications in the far interaction are reduced. An inner-group transition level is designed for switching partitions on the intermediate level between the hierarchical-structure partitioning and BP levels. The ternary strategy can realize as high parallel efficiency as the hierarchical partitioning strategy while maintaining flexibility in selecting the total number of processes. An auxiliary-tree-based parallel mesh refinement technique and a hybrid octree storage strategy are designed to facilitate the realization of fast full-wave simulation on a scale of over 10 billion unknowns with the ternary MLFMA. The accuracy of the solutions is validated by comparing the radar cross sections (RCSs) of a sphere of diameter 3042 wavelengths with 10 773 415 728 unknowns via the MLFMA and the Mie series, which is the largest number of unknowns to be computed via full wave numerical methods to date. Furthermore, the solutions for complicated objects, namely a ship and an aircraft model, both of which have maximum lengths that exceed 10 000 wavelengths and over 10 billion unknowns, are presented. [ABSTRACT FROM AUTHOR]

The nested dissection (ND) $\mathcal {H}$ -LU-based fast finite element (FE) direct solver is studied for scattering by large 3-D inhomogeneous objects. The special characteristics of the admissibility condition in FE method (FEM) are demonstrated comparing with those in the moment method. A weaker admissibility condition in FEM is proposed for higher efficiency than the conventional one. A better reduction scheme is presented for electrodynamic scattering problem. Numerical experiments show that our developed ND $\mathcal {H}$ -LU-based FE direct solver has O(NlogN) memory complexity and O(Nlog2N) CPU time complexity for a quasi-static problem, but a larger and irregular complexity for an electrodynamic problem. It has been compared with other most advanced direct sparse solvers and proved to have a better performance. A large realistic scattering problem with more than 10 million unknowns is calculated, showing the capability of our proposed ND-based $\mathcal {H}$ -LU direct FEM solver. [ABSTRACT FROM AUTHOR]

An accurate and efficient simulation model is developed for the scattering from a 3-D ship on a 2-D sea-like surface. The ship on the sea-like surface is modeled as a ship on a random surface with the impedance boundary condition. A full-wave simulation method is developed to simulate this model by using the self-dual integral equation and the parallel multilevel fast multipole algorithm. The simulation model is compared with the model of a ship on a flat surface and on a perfectly electrically conducting random surface, respectively. The application ranges of these models are concluded. Furthermore, the characteristics of the ship on a sea-like surface are studied by using the developed simulation model. [ABSTRACT FROM PUBLISHER]

The surface integral solution of scattering from multilayer dielectric bodies is studied in this letter. It is found that the matrix structure of discretized formulation for multilayer dielectric bodies has essential differences from that for homogeneous bodies since the formulation of multilayer dielectric bodies includes the interaction between equivalent currents on different interfaces. The previous efficient preconditioners for solution of homogeneous bodies are not efficient anymore or cannot be directly extended for solution of multilayer dielectric bodies. An efficient preconditioning approach is designed for multilayer dielectric bodies in this letter by recursively employing the Schur complement approximation and lower triangular approximation. The multilevel fast multipole algorithm is employed to further speed up the solution of multilayer dielectric problems. A series of numerical results are presented to show the capability of the preconditioning approach for multilayer bodies, especially for lossless large multilayer radomes. [ABSTRACT FROM PUBLISHER]

This paper incorporates the compensated Mitzner boundary conditions (CMBC) into the hybrid finite element- boundary integral-multilevel fast multipole algorithm (FE-BI-MLFMA) for fast and accurate computation of scattering by three-dimensional inhomogeneous objects with thin dielectric structures. In this CMBC-FE-BI-MLFMA, each thin dielectric layer is reduced to an interface with zero thickness; then CMBC is applied to establish the relation of electromagnetic fields across the interfaces. This approach can reduce the amount of computation and remain the advantages of versatility, accuracy, and efficiency of the conventional FE-BI-MLFMA algorithm. The formulation of this CMBC-FE-BI-MLFMA is presented in this paper. An efficient preconditioner based on the sparse approximate inverse is employed and further parallelized on memory-distributed platforms. Numerical results are presented to demonstrate the accuracy, efficiency, and capability of the parallel CMBC-FE-BI-MLFMA. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

An accurate bistatic scattering center model for cone-shaped targets is proposed in this paper. The model describes the overall attributes of dominant bistatic scattering centers. It includes not only the sliding scattering centers on the smooth surface and bottom edge, but also the scattering centers induced by creeping waves and traveling waves which are not considered in the previous models. To validate the proposed model, the results based on this model are compared with precise scattered fields computed by the full-wave numerical method, namely the hybrid finite element-boundary integral-multilevel fast multipole algorithm (FE-BI-MLFMA). Excellent agreement has been achieved. In contrast to the traditional assumption, it is concluded in this paper that the scattering centers of creeping waves and traveling waves are important, and can not be ignored particularly under bistatic mode. [ABSTRACT FROM PUBLISHER]

A skeleton-based wide-band algorithm (SBWBA) is proposed to efficiently evaluate radar cross section (RCS) from complex targets over a wide frequency band. The algorithm begins with generating a matrix, \widetilde\bf I, from which skeleton frequencies (SFs) are extracted by the proposed skeleton frequency extraction (SFE) strategy. The SFE strategy employs an adaptive manner to select SFs through the interpolative decomposition (ID) skeletonization. After the RCS results associated with the SFs are obtained, the complete wide-band response can be recovered through the ID efficiently. An inherent requirement for the employment of \widetilde\bf I and the SFE strategy is that the equivalent currents vary smoothly and slowly with frequency, which is satisfied only when the frequency band is sufficiently narrow. A multiinterval SFE strategy is developed as a remedy by automatically dividing the wide frequency band into several relatively narrow ones. Numerical experiments on complex targets have been performed to show efficiency and accuracy of the proposed SBWBA. [ABSTRACT FROM PUBLISHER]

A domain-decomposition-based preconditioner (DDP) is presented for the hybrid finite element-boundary integral-multilevel fast multipole algorithm (FE-BI-MLFMA). The formulation of FE-BI is first approximated by the finite element method (FEM) with absorbing boundary condition (ABC). Then this approximate FEM-ABC formulation is solved by using the finite element tearing and interconnecting method (FETI). Finally, an inner-outer iterative algorithm with variable convergence threshold is designed for FE-BI-MLFMA. Because of good numerical scalability of FETI and good approximation of FEM-ABC, this DDP-FE-BI-MLFMA performs well even for large lossless objects. [ABSTRACT FROM PUBLISHER]

The hybrid method of the finite element–boundary integral–multilevel fast multipole algorithm (FE-BI-MLFMA) has been recognized as one of the most powerful numerical methods for analyzing large inhomogeneous radiation/scattering problems. A domain decomposition algorithm (DDA) of FE-BI-MLFMA is presented in this paper by using the finite element tearing and interconnecting method (FETI). The formulation of DDA-FE-BI-MLFMA is presented and analyzed in detail. The numerical performance of DDA-FE-BI-MLFMA is investigated by numerical experiments from many aspects. It includes the convergence speed versus types of domain decomposition, number of subdomains, types and inhomogeneity of dielectrics involving in solved problems, and the scalability of DDA-FE-BI-MLFMA. The comparison of DDA and previous algorithms of FE-BI-MLMFMA is also carried out. Finally, the capability of DDA-FE-BI-MLFMA is shown for large inhomogeneous problems. [ABSTRACT FROM PUBLISHER]

The asymptotic waveform evaluation (AWE) technique has been widely used in the method of moment (MoM), the finite element method (FEM), and the hybrid finite element–boundary integral method (FE-BI) for fast computation over a wide frequency band. However, how to apply AWE to the multilevel fast multipole algorithm (MLFMA) still remains challenge. This paper proposes an efficient and robust approach to apply AWE to the hybrid finite element–boundary integral–multilevel fast multipole algorithm (FE-BI-MLFMA). The validity of the proposed approach is verified by numerical examples for scattering problems. Numerical experiments show that the application of AWE to FE-BI-MLFMA can greatly improve the efficiency of FE-BI-MLFMA for computation of scattering over a wide frequency band. [ABSTRACT FROM PUBLISHER]

Using OpenMP to further accelerate the pure MPI parallel MLFMA, an efficient and flexible parallel multilevel fast multipole algorithm (MPI-OpenMP-MLFMA) is proposed. Compared with previous MPI parallel schemes, the MPI-OpenMP-MLFMA improves the load-balance and scalability greatly. The computational capability of the proposed MPI-OpenMP-MLFMA is demonstrated by computing scattering from two extremely large targets: a sphere with a diameter of 1200 wavelengths, modeled by 1,063,706,700 unknowns, and an airplane model with the largest dimension of 1600 wavelengths, involving 288,151,344 unknowns. [ABSTRACT FROM PUBLISHER]