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The matrix enhancement and matrix pencil (MEMP) has been used to reduce the number of array elements in the planar array with a shaped-beam pattern. This work extends the MEMP-based synthesis method to the synthesis of pattern reconfigurable sparse planar arrays in wide angle scanning and wide-band, which exploits a necessary restriction on finding the common element positions and individual element excitations for multiple patterns. Moreover, a unitary transformation is exploited into the multiple-composite equivalent Hankel matrix, which converts the complex computations of singular value decomposition (SVD) and eigenvalue decomposition (EVD) courses into real ones and effectively reduces the computation complexity. A new tactic is also restricted on avoiding too small element spacing with the consideration of the size of array antenna element. A set of numerical experiments is provided to validate the effectiveness and advantages of the proposed method.

This paper addresses a novel rotationally symmetric technique with multiple constraints for sparse conformal array synthesis. The purpose is to synthesis a sparse optimal common element positions on the conformal surface varying multiple patterns of wide angle scanning with the behavior of low sidelobe levels (SLL). The conformal surface aperture is partitioned into several rotationally symmetric sections. The element positions and element numbers of only one section need to be optimized, which contribute to the reduction of optimizing variables and computation resources. We formulate the synthesis problem as a constrained optimization problem, which takes the peak sidelobe level (PSLL) as the fitness function, and sets the total number of array elements, the minimum spacing between two adjacent elements to form multiple constraints. The Brain Storm Optimization (BSO) is further exploited into the synthesis problem with multiple constraints. A set of representative numerical examples are presented to assess the advantages and effectiveness of the proposed method.

An equivalent fractional order orbital angular momentum (OAM) mode based on concentric uniform circular array (CUCA) is proposed in this paper. It is known that the azimuthal resolution of electromagnetic vortex imaging is closely related to the number of OAM modes. Although the multiple-in-multiple-out (MIMO) scheme gives better azimuthal resolution than the multiple-in-single-out (MISO) scheme, it suffers aliasing problem, which means the scattering points with their azimuthal difference larger than 180 degree can not be separated correctly. One possible way to solve this is adding fractional modes in MIMO scheme, but unfortunately, fractional modes are unstable and can not transmit to far field. In this paper, an equivalent fractional order OAM mode is introduced to deal with the problem to achieve higher azimuthal resolution by MIMO scheme. The transmitted and received modes are set to be two adjacent integer modes to realize an equivalent fractional mode. Since the radiation patterns generated by uniform circular array (UCA) for different modes are not aligned, concentric uniform circular array (CUCA) is applied and optimized to overcome this shortage. Simulation results demonstrate the validity of the proposed method.

An innovative noniterative approach based on the matrix enhancement and matrix pencil (MEMP) is proposed for the synthesis of arbitrary sparse planar arrays. In this study, the estimation of array parameters is recast as a 2-D pole extraction problem, and the number of array elements is minimized by the reduced rank processing. Subsequently, the Hankel matrix decomposition algorithm is exploited to accelerate the singular value decomposition (SVD) of the Hankel matrix constructed by the desired pattern samples, which conquers the restriction on the matrix dimension of the sampled Hankel matrix with the increasing of the number of array elements. The MEMP approach is further extended to the synthesis of shaped-beam patterns by using the forward–backward matrix enhancement and matrix pencil method (FBMEMP). A set of representative numerical experiments is provided to validate the effectiveness and advantages of the proposed method.

In human security, active millimeter wave imaging system has high sensitivity and is not easily affected by the environment. In this paper, the ray propagation theory of millimeter wave in lossy medium is introduced, the multiple scattering model is established, and the basic idea of active imaging simulation by using shooting and bouncing ray (SBR) method is given. In order to improve the efficiency of computation, GPU parallel technology is used to accelerate. Finally, the two-dimensional image of human body with a metal pistol in typical security scene is given.

This paper concentrates on harmonic analysis in gaseous helium, including microscopic generation, selective filtration and macroscopic propagation. A coherent method is proposed, with time-dependent Schrodinger equation for harmonic generation and Maxwell's wave equation for harmonic propagation. By introducing the polarization source based on the microscopic single-atom response, the macroscopic nonlinear propagation can be efficiently solved by a set of linear equations at each harmonic frequency. Using the proposed method, we numerically investigate the propagation effects of selective harmonics in gaseous helium. Our results reveal that specific harmonics allow the synthesis of an isolated attosecond pulse, which presents a high beam quality and an excellent spatial profile with Gaussian-like distribution. Moreover, the generated pulse provides a promising potential on high power defense, quantum radar and communication.

We propose a flat retroreflector that can efficiently reflect the electromagnetic waves back along its incident direction in a wide continuous range of angles. This retroreflector consists of a quadratic metalens and a flat metallic reflector at the focal plane of the former. The quadratic metalens is a dielectric pillar array encoded with a quadratic phase profile and it is embedded in the top side of the substrate. The flat reflector is on the bottom side of the substrate. The designed retroreflector has a diameter of 40 mm, a thickness of 15 mm, and a working frequency of 77 GHz. Through meta-units optimization, a retroreflection efficiency of 38.51% at ± 60° incidence and an average retroreflection efficiency of 46.39% for the incident angles from 0° to 60° can be numerically demonstrated. This flat retroreflector is easy for integration, which is promising for potential applications in the miniature wireless communication systems.

For tightly coupled antenna array, the evaluation of array radiation pattern by using array factor method always lead to unconvincing results, due to the neglect of the strong coupling between array elements. In this paper, an efficient optimization algorithm combining the characteristic mode(CM) method with genetic algorithm for tightly coupled antenna array is proposed. The fitness value of genetic algorithm is calculated by using CM method, which can ensure high calculation accuracy. Numerical example is given to show that the proposed method can be used to optimize the side lobe level(SLL) of the array accurately.

In this paper, a mixed inner–outer iteration technique based on surface integral equation is proposed for solving scattering problems from penetrable and homogeneous dielectric structures. The most important novelty of the proposed technique is combining the tangential Poggio–Miller–Chang–Harrington–Wu–Tsai as outer iteration and the electric-magnetic current combined-field integral equation as inner iteration, respectively. In this case, the new method offers the guarantee of high accuracy with faster convergence, especially for electrically dielectric structures in large scale. Furthermore, it presents an excellent compatibility with sparse approximate inverse preconditioning. Numerical results are given to demonstrate the accuracy, efficiency, and compatibility of the proposed method.

Three dimensional high-order discontinuous Galerkin time domain (DGTD) method is proposed to solve electromagnetic problems of dispersive media, which utilizes hierarchical basis function in space domain and Rung-Kutta iteration in time domain. The presented method is applied into the analysis of scattering problems of hypersonic aircraft which is coated with plasma. The hypersonic aircraft includes blunt cone model, missile model and metal warhead model. It is observed that high-order DGTD method reduces the number of unknowns greatly and accelerates the convergence against low-order DGTD. Numerical results are given to demonstrate the accuracy, efficiency, and compatibility of the presented method.

A novel technique incorporating the unitary matrix pencil (UMP) method is extended to the case of sparse linear arrays with wideband frequency invariant (FI) patterns. Multiple pattern data at different frequencies are formulated with the same poles corresponding to the FI element positions by a new sampling strategy. The unitary transform converts the complex computations for block Hankel matrices into real ones, which contributes to the reduction of the computation complexity for the singular value decomposition and the eigenvalue decomposition procedures. Taking advantage of the equivalent matrix pencil obtained by the unitary transformation, a new relation between the element positions and generalised eigenvalues can be built by the UMP method, which contributes to the real solutions for all element positions win wideband. A new tactics is exploited to avoid small element spacing with the consideration of the size of array antennas. Multiple FI patterns are reconstructed with a higher matching accuracy by only varying the excitation distributions. A set of representative numerical examples demonstrate the efficiency and advantages of the proposed method.

An efficient high order plane wave time domain algorithm is presented for analyzing the transient scattering from three dimensional electrically large conducting objects. This method uses a set of hierarchical divergence-conforming vector basis functions to accurately represent the current distribution on the perfect electrically conducting (PEC) surface. The higher order functions can significantly reduce the number of unknowns without compromise on the accuracy. The time domain combined field integral equation (TD-CFIE) is then discretized using the hierarchical divergence-conforming vector basis functions and shifted Lagrange polynomial functions in spatial and time domain, respectively. The final matrix equation can be accelerated using the plane wave time domain (PWTD) algorithm. Finally, a parallel algorithm that can execute on a distributed-memory parallel cluster is developed, which provides an appealing avenue for analyzing the transient scattering from three-dimensional electrically large complex PEC objects. Numerical examples are given to demonstrate the accuracy and efficiency of the method.

A novel time-domain volume integral equation (TD-VIE) is proposed to analyze the transient electromagnetic scattering from inhomogeneous dispersive objects. In this TD-VIE method, the higher order Nystrom method is applied in spatial domain. Namely, the curvilinear tetrahedron elements are utilized to discretize dielectric objects and resulting unknowns are volume electric current density. The Lagrange interpolation polynomials are used to represent spatial basis functions. In temporal domain, the marching-on-in-time (MOT) scheme is applied and the shifted Lagrange interpolation functions are used to represent temporal basis functions. Moreover, the point-matching method is applied both in spatial and temporal domain. Compared with the traditional spatial Schaubert–Wilton–Glisson basis based on TD-VIE, this novel TD-VIE method is more efficient. Several numerical examples have demonstrated that the proposed method is accurate, stable, and also more efficient than the traditional TD-VIE.

In this paper, we introduce the Ballistic-Diffusive equation for the Heat Conduction equation from nanometer to macroscopic description, which is suitable for nanoscale thermal characterization. And the spectral-element time-domain (SETD) method is applied to the solution of the Ballistic-Diffusive equation in one-dimensional simulation of semiconductor heat problem. The performance and accuracy of the proposed method were verified with literature data.

A nested complex source beam (NCSB) method based on octree structure is proposed to accelerate the method-of-moments (MoM) solution for three-dimensional (3-D) electromagnetic scattering analysis. At the finest level, the far-field contribution of each basis function is expressed with that of complex source beams (CSBs) distributed on the equivalent sphere surface for every group. Furthermore, the far field radiated by CSBs of the source group at child level can be represented by that radiated by CSBs of the source group at parent level. Similarly, the received field of CSBs for each observation group at the parent level can be expressed with that of CSBs belong to their child level group. An equivalent relationship of CSBs between every two adjacent levels is built to obtain the nested equivalent process for NCSB method, and only the CSBs at the finest level have the direct association with the basis functions in their group. The NCSB method is shown to be O(NlogN) computational complexity for both matrix–vector product (MVP) time and memory storage by numerical examples with appropriate parameters, and numerical results demonstrate the better efficiency of the proposed method than the current multilevel CSB method.

An efficient marching-on-in-degree (MOD) scheme is proposed to analyze the transient EM scattering from multiple conducting bodies of revolution (MBoRs) with arbitrary axis using the equivalence principle algorithm (EPA). The self-acting of each BoR is calculated by taking advantage of the rotationally symmetrical property in its local BoR coordinate system. The interaction between any two BoRs is replaced by the one between their equivalence spheres which enclose corresponding BoR with EPA. In this way, the transient scattering properties of the randomly distributed MBoRs can be obtained with high efficiency by the use of the BOR basis functions and the weighted Laguerre polynomial. Numerical results are presented to demonstrate the accuracy and efficiency of proposed algorithm.

This letter presents the nonlinear analysis of the physical characteristic of a microwave positive intrinsic-negative diode limiter using the field-circuit coupling algorithm based on a time-domain volume-surface integral equation method. In order to accelerate the Newton iteration solution of the nonlinear field-circuit coupling equations, an improved solution scheme of a matrix equation is used here. Moreover, the basic diode charge-control model employed contains both a forward and reverse process as well as emitter recombination. Experimental and numerical results are given to demonstrate the accuracy and the efficiency of the proposed method for the nonlinear analysis of commercial limiter.

This paper concentrates on simulation of multiscale plasmonic-enhanced nanoscale photovoltaics. A multiscale electromagnetics/quantum-mechanical (EM/QM) method is proposed to model the current-voltage characteristics and optical properties of plasmonic nanowire-based solar cells. The EM/QM method features a combination of classical Maxwell description for electromagnetic environment and first-principles quantum mechanical treatment for the photoactive component. The coupled optical-electrical EM/QM simulations demonstrate a dramatic enhancement for power conversion efficiency of nanowire solar cells due to the surface plasmon effect of nanometallic structures.

In this paper, a genetic algorithm (GA) with matrix mapping is proposed for the uniform amplitude sparse planar arrays with multiple constraints, which include the number of elements, the array aperture and the minimum distance between adjacent array elements. The proposed method transforms the multiple constraints problem to an unconstrained problem by establishing two mapping functions. Numerical experiments are provided to validate the effectiveness of the proposed method.

In this paper, Direction Of Arrival (DOA) estimation algorithm based on sparse representation of covariance matrix for four dimensional (4-D) antenna arrays with unknown source number is proposed to solve defect that DOA estimation needs to know source number in existing DOA estimation algorithms for 4-D antenna arrays. The algorithm represents sparse representation of covariance matrix for 4-D antenna arrays directly. The whole sparse reconstruction process does not need to know source number. Simulation results show that the algorithm can achieve accurate DOA estimation under unknown source number, low SNR, closely spaced signals and coherent signals.

In this paper, an all-metal Vivaldi antenna is designed. The metal baffles are loaded in this all-metal Vivaldi array along the H plane to eliminate the port mismatch problem when wide-angle scanning. The proposed antenna array exhibits a 4:1 (2 to 8 GHz) operating bandwidth while scanning at ±45 in the E-plane and H-plane with active VSWR

The work develops an extended multiple measurement vectors FOCUSS (M-FOCUSS) method for the synthesis of sparse array patterns with nonuniformly spaced linear arrays in wideband frequency. In the method, the synthesis result can obtain multiple pattern data of different frequencies having the best common element positions by virtue of the Multiple-Sensing-Matrices (MSM) scenario. Numerical examples show the high accuracy of achieving the desired radiation pattern in wideband frequency with maximally sparse non-uniform linear array.

This paper introduces a wide conformal quasi printed Log Periodic dipole band-notched antenna. The conformal band-notched antenna is composed of three sections-the low frequency structure, the band-notched structure and the high frequency structure. Installing to the interior of a radome, radiation characteristics of the antenna are very good. The simulation results revealed that the antenna has good VSWR(less than 2) and radiation pattern of realized gain over the design frequnecy range of 3GHz to 6.2GHz and 8GHz to 12GHz.

The transient EM scattering from a homogeneous dielectric body of revolution (BOR) is formulated in terms of the time-domain PMCHW (TD-PMCHW) integral equation. Triangular functions along the generatrix of the BOR and weighted Laguerre polynomials are used as the spatial and temporal basis functions, respectively, to expand the unknown equivalent surface electric/magnetic current densities. In this way, both the memory requirement and the CPU time can be reduced largely since the matrix equation for each Fourier mode can be solved independently. Numerical results are presented to demonstrate the feasibility of the proposed method. Moreover, the convergence is discussed for both the weighted Laguerre polynomials and the Fourier mode.

As a powerful variant of the dual-primal finite-element tearing and interconnecting (FETI-DP) method in electromagnetics (EM), the FETI-DPEM method shows excellent convergence properties and numerical scalability. A key factor affecting the performance of the FETI-DPEM is the direct solution of sub-domain FE systems. An efficient direct solver based on hierarchical (ℋ-) matrix technique is proposed to solve the sub-domain FE systems. ℋ-matrix formatted lower-upper (LU) decomposition with subsequent forward and backward substitution (FBS) can significantly reduce the computational costs of the direct solution with sufficient accuracy. The nested dissection technique is employed to further accelerate the ℋ-LU decomposition and the ℋ-FBS. Numerical examples demonstrate that the proposed method is very robust for the three-dimensional EM simulation.

This letter proposes a fast method that combines the complex-source beam (CSB) and multilevel fast multipole algorithm (MLFMA) for electromagnetic (EM) scattering problems. The CSB for the MLFMA is obtained by introducing an imaginary part for the independent variable of the spherical Hankel function in the translation operator, which makes the translation operator directional. Furthermore, a window function is introduced in the translation operator to make it more directional. A large part of the angular translation operators are then discarded with an angle threshold. Numerical examples demonstrate that the translation operator memory cost can be reduced significantly compared to the MLFMA, and more accurate results can be obtained compared to the ray-propagation multilevel fast multipole algorithm (RP-MLFMA).

This letter concentrates on an efficient time-domain integral equation (TDIE) method based on the marching-on-in-time (MOT) scheme for the analysis of the transient electromagnetic scattering from discrete body of revolution (DBOR). Taking advantage of the discrete circular symmetry, the storage requirements can be reduced significantly. Further computational efficiency can be improved by using the fast Fourier transform (FFT) technique to accelerate the matrix vector product. Numerical examples are given to validate the accuracy and efficiency of the proposed method.

A fast wideband electromagnetic scattering analysis method based on Taylor expansion and higher order hierarchical vector basis functions is proposed. By extracting a phase term from the green function, the remaining exponent term can be approximated by its Taylor expansion. After that, some computationally intensive matrices related to the geometry of the object can be computed in advance. During the frequency sweeping process, the impedance matrix is generated efficiently by combining the precomputed matrices and some frequency dependent terms. By using higher order hierarchical vector basis functions, only one coarse mesh corresponding to the lowest frequency of the given frequency band is generated. The order of the basis functions increases with the rising of frequency. Moreover, only the precomputed matrices corresponding to the highest order basis need to be computed. All impedance matrices at different frequencies can be generated by these precomputed matrices due to the hierarchical property of the basis functions. The proposed method is implemented in the platform of the multilevel fast multipole algorithm (MLFMA). Numerical results show that the proposed method can efficiently accelerate the wide-band scattering analysis.

This letter proposes a multilevel complex source beam (MLCSB) method for electromagnetic (EM) scattering problems. The multilevel structure is obtained with the octree grouping technique. Each basis function in the nonempty group is expanded with CSBs that tightly surround the group. The interactions between far groups are expressed with interactions of these CSBs. To accelerate the computation, the symmetry and shift invariance of the Green’s function is employed. The adaptive cross approximation (ACA) algorithm is then applied to accelerate the computation of interactions of CSBs. Due to the directionality of the radiation pattern of the CSBs, the interactions of CSBs are truncated with an angle threshold. Numerical examples demonstrate the efficiency of this method.

An efficient multilayer thin dielectric sheet (TDS) formulation based on the marching-on-in-time (MOT) solver is proposed for the analysis of transient electromagnetic scattering from a conductor coated by multilayer thin materials. Like its frequency domain counterpart, all the sources in the thin dielectric coatings are represented in the terms of current densities on PEC surface. The proposed method can reduce the number of unknowns significantly while reasonable accuracy can be achieved. Several numerical examples are presented to demonstrate the accuracy and stability of the proposed method.

A new manifold learning algorithm named adaptive neighborhood preserving discriminant projection method is proposed for the feature extraction of high-range resolution profile (HRRP)-based radar target recognition. By utilizing the objective functions of both neighborhood-preserving projection (NPP) and adaptive maximum margin criterion (AMMC), the proposed method can not only preserve the neighborhood structure of original data in the dimensionality reduced space, but also exhibit good classification performance. The proposed method is applied to the feature extraction of HRRP-based radar target recognition. Numerical experiments show that the proposed method can effectively reduce the dimensionality of HRRP and give satisfactory recognition rate.

This communication presents a new numerical method for the efficient solution of marching on in time (MOT)-based time domain integral equations (TDIE) for electromagnetic scattering from perfect electrically conducting (PEC) object with large smooth surfaces. A set of space-delayed temporal basis functions is proposed for the temporal discretization, and the curvilinear Rao-Wilson-Glisson (CRWG) basis functions for the spatial discretization. The space-delayed temporal basis functions are firstly extended to the time domain electric field integral equations (TDEFIE), then easily to the time domain combined field integral equations (TDCFIE). Numerical results demonstrate that the new method is stable and effective for the transient scattering problems from PEC objects with large smooth surfaces and a single plane wave incidence. A significant reduction of the number of spatial unknowns is achieved by using the space-delayed temporal basis functions.

This paper proposes a multigrid preconditioner for integral equation fast analysis of electromagnetic scattering problems. The multigrid model is constructed by recursively dividing every triangular element on the coarse level into 4 small ones. The Rao–Wilton–Glisson (RWG) basis functions defined on the coarse level are expressed with linear combinations of those on the fine level, and the expansion coefficients of which are used to construct the restriction and interpolation operator. To further accelerate the convergence of iterative solution, a set of solenoidal basis functions on the coarse level are constructed additionally, which are also expressed with linear combinations of RWG basis functions on the fine level and adopted to construct the second restriction and interpolation operator. The two sets of coarsening techniques are then combined together to remove the low-frequency components of the iterative error. Numerical results show that the proposed method can reduce both the steps of iteration and CPU time compared with the iterative solver without preconditioning.