Zi-Liang Liu

Efficient Iterative Method of Moments—Physical Optics Hybrid Technique for Electrically Large Objects

The conventional hybrid method of moments (MoM)-physical optics (PO) technique provides a possible way to handle electrically large objects with affordable computer memory. However, its efficiency is not very good because the evaluation of the PO contribution to the MoM impedance matrix is very time-consuming. An efficient implementation of the iterative MoM-PO hybrid technique is presented in this paper to avoid the calculation of the PO contribution in matrix form. For electrically large objects, the proposed efficient iterative MoM-PO (EI-MoM-PO) method can greatly reduce the computational time and maintain the same or better accuracy with the same number of unknowns compared with the conventional MoM-PO method. Several examples of large-scale structures are analyzed by the EI-MoM-PO method, the conventional MoM-PO method, and the multilevel fast multipole algorithm. The excellent efficiency and accuracy are achieved by the proposed EI-MoM-PO technique.

Installed Performance Modeling of Complex Antenna Array Mounted on Extremely Large-Scale Platform Using Fast MoM-PO Hybrid Framework

A fast method of moments-physical optics (MoM- PO) hybrid framework is proposed to efficiently analyze complex antenna array mounted on large-scale platforms with multi-scale features. In this fast MoM-PO hybrid framework, the MoM, enhanced by the adaptive integral method (AIM), is employed to effectively simulate the antenna array, and the PO is used to efficiently describe the perturbation from the large platform on the antenna array. An iterative process is implemented to capture the interaction between the antenna array and the platform for achieving stable and converged solution. The proposed hybrid framework provides very good flexibility to cater for any fast integral equation solvers for speeding up the MoM solution process in modeling large and complex antenna arrays. Numerical simulations clearly demonstrate that the proposed fast MoM-PO technique is capable of handling complex onboard antenna arrays installed on electrically large platforms with much less computational costs as compared with the conventional MoM-PO method and multilevel fast multipole algorithm (MLFMA).

Implementing PTD efficiently for electrically large objects

Summary form only given. Modeling electromagnetic characteristics of electrically large and complex objects is challenging. Electromagnetic interaction can be complicated. Every modification to part of a structure requires re-analyzing the structure. This is tedious and time-consuming. Therefore, mathematical tools that enable fast modeling of electromagnetic characteristics is crucial in understanding the scattering behavior of electrically large and complex object. Full wave methods like method of moments (MOM) and multilevel fast multipole method (MLFMM) have been improved tremendously over the years and are invaluable. However, they are still far from ideal to fit into the workflow at design phase due to huge computational cost. A better tradeoff to meet aggressive timeline is to perform rapid prototyping using hybrid high frequency methods. In practice, physical optics (PO), shooting and bouncing rays (SBR) and physical theory of diffraction (PTD) are reasonably accurate at predicting most significant scattering signature of electrically large object. With such rapid prototyping tools, engineers are able to quickly identify electromagnetic issue in early stage. Fast and accurate prediction of scattering behavior also enables engineers to quickly iterate between solutions to explore design tradeoffs. In addition to high performance computing facility, this even opens up the capability to perform parametric studies. With PO and SBR implemented efficiently on graphic processing unit (GPU), we question the underutilized central processing units (CPUs) in our application. We have decided to explore the potential of modern CPUs and this paper discusses an efficient implementation of PTD on modern CPUs. In particular, we stress the combination of efficient algorithms and appropriate data structure in order to achieve great performance. Numerical result shows good accuracy and efficiency tradeoff to those obtained from MOM.

Development of hybrid high frequency simulation tool for rapid modeling of electromagnetic scattering from large and complex structures

To rapidly capture the electromagnetic scattering behavior of electrically large and complex structures, we have developed a hybrid high frequency (HF) simulation tool through the combination of different asymptotic methods, such as physical optics (PO), shooting and bouncing rays (SBR), and physical theory of diffraction (PTD). Careful consideration of integrating PO, PTD, and SBR together ensures good accuracy of the hybrid HF tool. Effective implementation of the hybrid HF tool with using the state of the art GPU and CPU high performance computing (HPC) techniques greatly speeds up the solution process of modeling backscattering from electrically large and complex objects for rapid design. It should be noted that, differing from fast full wave simulation methods, the hybrid HF simulation tool uses different HF technique to handle different scattering wave component to understand its underlying physics and effects on total scattering responses, which is very important for complex structure design.

Fast analysis of electromagnetic scattering problems using SAIM-FAFFA method

A subdomain adaptive integral method (SAIM) in conjunction with the fast far-field approximation (FAFFA) technique is presented for fast analysis of electromagnetic scattering from 3D PEC objects. In the SAIM technique, the whole structure is divided into several subdomains and each subdomain is properly enclosed in its local Cartesian grid. Then the AIM is applied to reduce the matrix storage and accelerate the matrix-vector multiplication for each subdomain. A current continuity boundary condition between adjacent subdomains is introduced to ensure the accuracy. Moreover, the FAFFA technique is adopted to speed up the process of updating the modified excitation vectors. Numerical results show that good accuracy of the proposed SAIM-FAFFA is achieved.

Efficient analysis of complex onboard antenna with large-scale platform by combining preprocessed data with hybrid MoM-PO method

A new and general hybrid scheme consisting of the method of moments (MoM) and the physical optics (PO) is presented for the efficiently modeling of complex antennas installed on large-scale platforms. Different from the conventional MoM-PO, the proposed general hybrid technique is more flexible to handle arbitrary onboard antennas by integrating preprocessed data of antennas into the hybrid scheme. With this new hybrid technique, we can conveniently predict the disturbed onboard antenna performance even without the detailed configuration of the antenna. Numerical results show good efficiency and accuracy of the proposed hybrid technique.

Fast frequency sweeping technique based on AIM-PO hybrid method

A new fast frequency sweeping technique hybridized with the adaptive integral method (AIM)-physical optics (PO) is proposed for wide-band response analysis. The AIM-PO is an efficient technique for modeling the large-scale structure with small features. However, the calculation of the response over a broad frequency band is very time-consuming. To achieve fast frequency sweeping, the Chebyshev approximation technique (CAT) is combined with AIM-PO through the expansion of the unknown equivalent currents into a Chebyshev series. Compared with the direct point-by-point simulations, much less Chebyshev sampling points are required. Therefore, the proposed AIM-PO-CAT method can significantly reduce the computational time without loss of accuracy.

A subdomain adaptive integral method for arbitrarily shaped objects

A novel subdomain adaptive integral method (SAIM) is presented for fast analysis of electromagnetic radiation and scattering from three dimensional objects of arbitrary shape. In conventional AIM, a uniform Cartesian grid is built up to entirely enclose the object, and auxiliary point sources are used to efficiently calculate far-zone interactions. However, adopting one Cartesian grid will actually cause large amount of auxiliary point sources redundant for the far-zone interaction calculation. To reduce the excess of those redundant auxiliary point sources, in the proposed SAIM, the whole domain is divided into several subdomains and then each subdomain is properly enclosed in its smaller Cartesian grid. Furthermore, the current continuity boundary condition between adjacent subdomains is employed to ensure the accuracy. Compared with the conventional AIM, the proposed SAIM technique can significantly reduce the number of auxiliary point sources and improve the convergence of iterative process. Numerical examples show the accuracy and efficiency of the proposed technique.

The hybrid higher-order MoM-UTD formulation for electromagnetic radiation problems

This paper presents a new efficient hybrid higher-order MoM-UTD method. It overcomes the limitation of traditional MoM-UTD method, which is difficult to be applied to the arbitrary structures because of complex ray tracing. Using the large quadrilateral patches and higher order basis functions, the hybrid method in this paper can save much more computer memory than the traditional low-order MoM with RWG basis functions. So it is feasible for complex and electrically large structures. Good accuracy is achieved as the numerical results illustrated.

Improved current continuity boundary condition of hybrid MoM-PO method

The current continuity between the MoM and PO regions is one of the crucial problems to limit the accuracy of the hybrid MoM-PO method. A new improved current continuity boundary condition for the method of moments (MoM) region and the physical optics (PO) is presented. This new boundary condition utilizes the excellent flexibility of the fast MoM-PO iterative scheme to avoid the implicit boundary condition enforced by the RWG basis functions. Numerical results show the good accuracy of the improved boundary condition.