A Characteristic Mode-Based MoM/SBR Hybrid Method for Scattering Analysis of Array Structures above a Rough Surface

A new efficient hybrid technique is presented, which combines the method of moments (MoM) and the shooting and bouncing ray (SBR) for analyzing scattering of complex large structures. By applying the SBR method for the whole structures, a corrected incident field including not only the direct incident field but also the multi-bounce field from the SBR region contributes to the integral equation in the MoM region. For the SBR region, it also considers the interaction from MoM region and then a physical optics (PO) type integration is performed to calculate the scattered field. For complex electrically large electromagnetic problems, the proposed technique is more efficient and simpler to implement in a general-purpose computer code. Numerical results are presented to show the efficiency and accuracy of the method.

An advanced two-scale model of EM backscattering from rough surfaces

The shooting and bouncing ray (SBR) method is effectively implemented on the graphics processing unit (GPU) for scattering problems of electrically large complex target and randomly rough surface composite model. Results obtained using the proposed approach are compared against results generated by commercial software and those obtained with the CPU-based SBR. The good agreement and significant acceleration show that the newly developed method is capable of modeling the composite scattering from complex and electrically large targets over a randomly rough surface.

Two ray shooting methods for computing the EM scattering by large open-ended cavities

The site-specific radio wave propagation prediction in outdoor is increasingly important for electromagnetic interference analysis. Since the outdoor environment is usually very complex and electrically large, the shooting and bouncing ray (SBR) method (one technique of ray tracing) rather than other numerical methods such as finite difference time domain method and finite element method, is often applied in the computation. However, a large amount of rays have to be launched to guarantee the accuracy in conventional ray tracing methods. This, in turn, increases the simulation time significantly. Recently, many acceleration algorithms have been reported including space partitioning and wavefront decomposition. This paper presents a novel adaptive ray launching (ARL) method based on the pattern of transmitting antenna, which reduces the launched ray number significantly while maintaining the computation accuracy

Radar detectability reducing for complex shape military or civil object is very important problem of contemporary radar theory. Solution of this problem is unthinkable without providing numerical estimations of the investigated object Radar Cross Section (RCS) and its reduction with some cloak. In this paper a new method for the semitransparent cloak modeling is proposed. This method is realized in the framework of Shooting and Bouncing Ray (SBR) method. General stages of SBR method and the cloak modeling introduction into its algorithm are discussed. The proposed approach was tested on an example of complex shape object.

The spectral theory of diffraction (STD) is well known for its ability to deal with complex fields (creeping waves, shadow limit fields, caustics fields) and their transformations through multiple diffractions. We present a fully numerical and 3-D implementation of this method. This implementation is based on a ray-tracing representation of plane waves propagation and it takes advantage of the simplicity of the plane waves transformation formulas at dielectric or conducting interfaces. The geometrical optics ray-tracing part of the procedure is quite similar to what is done in the shooting and bouncing rays (SBR) method, which has been applied to scattering calculations. However, the final evaluation of the field is performed through a spectral domain integration in our spectral domain ray tracing (SRT) method, instead of a physical optics integration in the SBR method. We give an outline of the principles of the method, and present the application of the method to substrate-lens antenna analysis. Simulated results obtained through this method are compared to results obtained through a more classical physical optics analysis, and to measured far-field radiation patterns of the antenna.

In this article, an efficient and systematic method for fast and accurate computation of characteristic modes (CMs) and eigenvalues of the entire array antenna as a whole is proposed. This technique benefits from the symmetry and Toeplitz property of the method of moments (MOM) impedance matrix of the array structure. Using this technique, we are able to directly obtain CMs of a large-scale array structure with minimal computational resources. First, the self-impedance matrix of a radiating element and the mutual-impedance matrices between that element and the remaining ones are calculated numerically using MOM. Then, the theory of characteristic modes (TCM) is applied to the entire array. Using the proposed method, we decompose the coefficient matrix of the CM equation into smaller matrices. In addition, interesting and meaningful relations between currents flowing on elements associated with each CM of an array are derived and used to significantly reduce the computational complexity in the CM extraction. Moreover, numerical results and computation time are reported to validate the proposed method.

In the paper, high resolution range profile (HRRP) of a target above rough ground is analyzed based on the scattered echo data. The electromagnetic scattering of composite model is solved by the hybrid method of physical optics (PO)- shooting and bouncing ray (SBR). And an octree data structure is used to accelerate the ray tracing progress. The bistatic electromagnetic scattering of a reduced-scale vehicle target above rough ground is calculated by our method and compared with the simulation result with MLFMM in FEKO. Then by inverse Fourier transform of backscattering echo data, the range profile of composite model is obtained.

ABSTRACTA generalized hybrid scheme combining finite element method (FEM) and the method of moments (MOM) is first presented to investigate scattering from a 3-D dielectric object above a 2-D dielectric rough surface. The hybrid FEM/MOM scheme is divided into the FEM region for the object based on Helmholtz’s equation and the MOM region for the rough surface based on coupled integral function, which can greatly reduce the computed region. With the rough surface getting larger, the unknowns of the rough surface get more. So MLFMA is employed to reduce computation complexity of MOM region itself and coupling interaction matrices between MOM region and FEM region. Consequently, the iterative process can be greatly accelerated. This generalized hybrid FEM/MOM is very suitable for investigating scattering from composite model of a complex material object and electrically large dielectric rough surface. Some examples verify this generalized hybrid FEM/MOM in high efficiency, low storage requirement, high precision and generality.

The actual rough sea surface is described by Pierson-Moscowitz (PM) spectrum and Monte Carlo method; the composite electromagnetic scattering from the double rectangular crosssection conductor columns above the rough sea surface is investigated using the hybrid methodthe Method of Moment with the Kirchhoff approximation. Angular distribution curves of composite scattering coefficient are obtained; and this coefficient that varies with the parameter of sea surface, rectangular cross-section conductor columns and incident waves is calculated in detail. The characteristics of the composite scattering coefficient from the double rectangular cross-section conductor columns above the rough sea surface are also obtained. Results show that the hybrid methodthe Method of Moment with the Kirchhoff approximation, compared to the traditional Method of Moment, can obtain higher accuracy. Moreover, the hybrid method can effectively reduce the computation time and memory footprint, and the performance becomes more favorable with the increase of the sizes of rough surface.

A Gaussian Schell Model (GSM) might be a convenient way to model extended beacons created on diffuse targets. Earlier, we used a full wave computational technique called the Method of Moments (MoM) to evaluate the scattered field from a rough impedance surface in vacuum. The MoM model showed several deviations from GSM. The present work uses a simulation approach based on physical optics approximation to study the scattering behavior in presence of atmospheric turbulence. A fully coherent beam is propagated through weak turbulence and is incident on the rough surface. The light scattered from the rough surface is again propagated through turbulence back to the source plane and the properties of the scattered radiation are studied through numerical simulations. The simulation results are compared with a GSM.

An efficient multiregion model is extended with the single integral equation (SIE) method to calculate the EM scattering from a dielectric rough surface. In the multiregion model, the rough surface is divided into multiple regions depending on their positions along the rough surface as well as the energy distribution of the incident wave. Two intermediate regions are chosen as the domain region on which the method of moment (MoM) is adopted. The mutual couplings between different regions are considered approximately based on the magnetic and field integral equations, from which closed-form approximations for electric current on other regions are derived.

The effect of building layout in street-cell model on path loss is investigated by using shooting and bouncing rays (SBR) method. A comparison of path loss between measurement and simulations of two different models confirms that only buildings along measurement path contribute mainly, while the others can be neglected. Our prediction results have been found to match well with the measurement results.

We present a method to generate three-dimensional (3D) inverse synthetic aperture radar (ISAR) images of a target at arbitrary aspect angles using the shooting and bouncing ray (SBR) method. We have derived a 3D-image-domain ray-tube integration formula based on the SBR technique. The imaging formula is in a form of convolution, then a nonuniform fast Fourier transform (NUFFT) is induced to achieve the convolution, which can be used to generate 3D ISAR images rapidly. Compared to the conventional algorithm where the ISAR images are obtained by inverse Fourier transforming the computed scattered fields over a range of frequencies and a range of aspect angles, the new formula needs only one-time ray tracing and physical optics (PO) integration over a small angle span. Hence the computational time is decreased tremendously. The ISAR images of a missile target and an armored car for several aspect angles are presented to demonstrate the efficiency and accuracy of the proposed method.