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The matrix pencil method (MPM) has been used to reduce the number of elements in the linear antenna array with a pencil-beam pattern. This work extends the MPM-based synthesis method to the synthesis of shaped-beam patterns by using the forward-backward matrix pencil method (FBMPM). The FBMPM-based synthesis method places a necessary restriction on the poles which correspond to element positions, and consequently obtains more accurate synthesis results, particularly for the synthesis of asymmetric patterns. Numerical examples show the effectiveness and advantages of the proposed method in the reduction of the number of elements for shaped-beam patterns. [ABSTRACT FROM AUTHOR]

A prototype microwave imaging system for imaging 3-D targets in layered media is developed to validate the capability of microwave imaging with experimental data and with 3-D nonlinear inverse scattering algorithms. In this experimental prototype, the transmitting and receiving antennas are placed in a rectangular tub containing a fluid. Two plastic slabs are placed in parallel in the fluid to form a five-layer medium. The microwave scattering data are acquired by mechanically scanning a single transmitting antenna and a single receiving antenna, thus avoiding the mutual coupling that occurs when an array is used. The collected 3-D experimental data in the fluid are processed by full 3-D nonlinear inverse scattering algorithms to unravel the complicated multiple scattering effects and produce 3-D digital images of the dielectric constant and conductivity of the imaging domain. The image reconstruction is focused on the position and dimensions of the unknown scatterers. Different dielectric and metallic objects have been imaged effectively at 1.64 GHz. [ABSTRACT FROM AUTHOR]

A new method combining the spectral integral method and spectral element method (SIM-SEM) is proposed to simulate 3-D electromagnetic scattering from inhomogeneous objects. In this hybrid technique (a special case of the finite element boundary integral (FEM-BI) combination), the SEM with the mixed-order curl conforming vector Gauss-Lobatto-Legendre (GLL) basis functions are used to represent the interior electric field with high accuracy, while the SIM on a cuboid surface is used as an exact radiation boundary condition. The Toeplitz property of the SIM matrix is utilized to reduce the memory and CPU time costs in an iterative solver by using the fast Fourier transform algorithm. Unlike the traditional FEM-BI combination where the BI portion usually dominates the computational complexity, the computational costs are much lower in the SIM-SEM method. Numerical results verify the accuracy and capability of this method, confirming that the SIM-SEM method is a good alternative for solving scattering problems from inhomogeneous objects. [ABSTRACT FROM AUTHOR]

A high-precision integration (HPI) scheme combined with the spectral-element time-domain (SETD) method is presented to solve the time-dependent Maxwell's equations. Spatial discretization by spectral elements will lead to block diagonal mass matrices, thus greatly alleviating the computational burden of inverting the mass matrices. A high-precision time integration method based on the matrix exponential is then employed to solve the discretized SETD system. Numerical examples demonstrate that this algorithm is unconditionally stable and very accurate. [ABSTRACT FROM AUTHOR]

A discontinuous spectral element time-domain method is proposed to analyze transient electromagnetic properties of general 3-D structures. This method is advantageous in that its mass matrices are block-diagonal due to the Gauss-Lobatto-Legendre polynomials, and it allows different orders of basis functions for each subdomain. The Riemann solver is employed in the boundary integral terms to communicate fields between adjacent subdomains. Perfectly matched layers are utilized to truncate the computational domain. Galerkin method is used for spatial discretization, and a fourth-order Runge-Kutta scheme is employed for the time integration. The validity of the proposed approach is demonstrated through several numerical examples of initial value problems and scattering problems. [ABSTRACT FROM AUTHOR]

Abstract-The synthesis of a nonuniform antenna array with as few elements as possible has considerable practical applications. This paper introduces a new non-iterative method for linear array synthesis based on the matrix pencil method (MPM). The method can synthesize a nonuniform linear array with a reduced number of elements, and can be also used to reduce the number of elements for linear arrays designed by other synthesis techniques. In the proposed method, the desired radiation pattern is first sampled to form a discrete pattern data set. Then we organize the discrete data set in a form of Hankel matrix and perform the singular value decomposition (SVD) of the matrix. By discarding the non-principal singular values, we obtain an optimal lower-rank approximation of the Hankel matrix. The lower-rank matrix actually corresponds to fewer antenna elements. The matrix pencil method is then utilized to reconstruct the excitation and location distributions from the approximated matrix. Numerical examples show the effectiveness and advantages of the proposed synthesis method. [ABSTRACT FROM AUTHOR]

In this paper, we present an enlarged cell technique (ECT) to avoid the time step reduction encountered in the conformal finite-difference time-domain (CFDTD) method due to small irregular cells truncated by metallic boundaries. We focus our efforts on the discussion of the accuracy and stability of the ECT and its comparison with other conformal methods, especially the one called the uniformly stable conformal (USC) method. We also provide a simplified ECT, which is much easier to implement. In the ECT, a stability criterion is first constructed to identify instable irregular cells, i.e., those having so small an area to cause instability. Those instable cells are then enlarged into their adjacent cells to obtain a large, stable area. Careful treatment is performed on the communication between the intruding and intruded cells in terms of electromotive force by keeping the total electromotive force conservative. This technique is verified by several 3-D numerical experiments. Results show that the ECT is second-order accurate and numerically stable at the regular Courant time step limit. [ABSTRACT FROM AUTHOR]

We propose a hybrid technique combining the pseudospectral time-domain (PSTD) method with the alternating-direction implicit conformal finite-difference time-domain (ADI-CFDTD) method to solve 3-D mixed-scale problems in computational electromagnetics. A mixed-scale problem contains both electrically large and relatively homogeneous regions and electrically small fine details, thus poses a significant computational challenge to any single computational method if it is utilized alone. In particular, the ADI-CFDTD method is an unconditionally stable time-domain method with second-order spatial accuracy, and allows the time step to be increased beyond the Courant-Friedrichs-Levy limit; it is suitable for electrically small problem (structure details much smaller than a wavelength) but is inefficient and suffers from large numerical errors for electrically large-scale regions. The PSTD method, on the other hand, is accurate and efficient for regions with large, relatively homogeneous materials, but loses its efficiency for electrically small structures. The hybrid PSTD/ADI-CFDTD method overcomes these disadvantages and is potentially more useful than the individual solvers. The implementation details and numerical accuracy of this hybrid method are examined. Numerical examples demonstrate the advantages of the hybrid PSTD/ADI-CFDTD method. [ABSTRACT FROM AUTHOR]

A spectral integral method is presented for electromagnetic scattering from dielectric and perfectly electric conducting (PEC) objects with a closed boundary embedded in a layered medium. Two-dimensional layered medium Green's functions are computed adaptively by using Gaussian quadratures. The singular terms in the Green's functions and the non-smooth terms in their derivatives are handled appropriately to achieve exponential convergence. Numerical results, compared with the ones obtained by using other methods, demonstrate the spectral accuracy and high efficiency of the proposed method. They also confirm that the spectral integral method (SIM) is applicable to concave objects. [ABSTRACT FROM AUTHOR]

Electromagnetic time-reversal imaging is addressed for a target situated in a cluttered background. We first investigate the theory of electromagnetic time-reversal imaging, followed by an experimental demonstration. A transmitter-receiver antenna array is connected to a network analyzer and applied to transmit wideband waveforms for detecting a target within a cluttered environment. We assume the cluttered background is fixed, thus the target signature is extracted by observing changes manifested by the introduction of a target. A numerical algorithm is required for computation of the Green's function employed within the time-reversal imager, with this implemented here via ray tracing. Example time-reversal images of different cluttered backgrounds and different targets are presented using measured data, with comparisons to a traditional radar imaging technique. Results show that the time-reversal imagery yields good focusing at the target, significantly better than when the background is not accounted for. [ABSTRACT FROM AUTHOR]

We have developed a fully three-dimensional electromagnetic inverse scattering technique in a multilayered medium via the contrast source inversion. The key issues on the three-dimensional (3-D) forward and adjoint operations related to the dyadic Green's operators are briefly addressed to ensure the efficient performance of the algorithm in layered media. It is shown that it is feasible to achieve good reconstruction quality with only a few sources and a two-dimensional receiver array, provided that the signal-to-noise ratio is adequate. The effects of the interface and of the uncertainty in the background layered medium are illustrated in the simulation. The developed 3-D electromagnetic inverse scattering technique can be effectively applied to surface ground penetrating radar survey in multilayered media. [ABSTRACT FROM AUTHOR]

A newly developed iterative method, the stabilized biconjugate gradient fast Fourier transform (BCGS-FFT) method is applied to simulate electromagnetic scattering from large inhomogeneous objects embedded in a planarly layered medium. In this fast solver, the weak-form formulation is applied to obtain a less singular discretization of the volume electric field integral equation. Several techniques are utilized to speed up the dyadic Green's function evaluation. To accelerate the operation of the dyadic Green's function on an induced current (i.e., the "Green's operation"), the Green's function is split into convolutional and correlational components so that FFT can be applied. The CPU time and memory cost of this BCGS-FFT method is O(N log N) and O(N), respectively, where N is the number of unknowns, significantly more efficient than the method of moments (MoM). As a result, this method is capable of solving large-scale electromagnetic scattering problems in a planarly layered background. A large-scale scattering problem in a layered medium with more than three million unknowns has been solved on a Sun Ultra 60 workstation with 1.2 GBytes memory. [ABSTRACT FROM AUTHOR]

In this paper, we apply a fast Fourier transform (FFT) accelerated volume integral equation solver to compute the radar cross section of large-scale inhomogeneous objects. This method is related to Bojarski's k-space method and the subsequent conjugate-(CG) and biconjugate-gradient (BCG) FFT algorithms. The method developed here combines the weak-form discretization with the BCG and stabilized BCG (BCGS) solvers. We show that this method has marked improvements over related algorithms. The numerical method has been validated by Mie series for multilayer spheres and applied to some practical problems. With this method we are currently able to solve a three-dimensional problem with a volume of size 3648λ³ (21.23 million unknowns) on a single workstation. [ABSTRACT FROM AUTHOR]

A 2.5-D multidomain pseudospectral time-domain (PSTD) method with a suitable well-posed perfectly matched layer is developed as an accurate and flexible tool for the simulation of electromagnetic wave propagation and scattering in conductive and inhomogeneous media. This approach allows for an accurate treatment of curved geometries with a high efficiency. Numerical results show an excellent agreement with analytical solutions for lossy dielectric cylinders. The 2.5-D multidomain PSTD algorithm is applied to several scattering and waveguiding problems. [ABSTRACT FROM AUTHOR]

Develops a pseudospectral time-domain (PSTD) algorithm to overcome limitations in the conventional solution methods for Maxwell's equations in cylindrical coordinates. Main contributions of the algorithm; Use of a coarse grid close to the Nyquist sampling density; PSTD and analytical results for a magnetic line source in a two-dimensional homogeneous medium.