Efficient IEFFT and PO Hybrid Analysis of Antennas around Electrically Large Platforms_jinlong
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Author:Ji Ma Abstract: An efficient hybrid analysis which combines integral equations (IE) with physical optics (PO) approximation is presented for antennas around an electrically large platform. In the analysis, the whole surface of the platform and antennas is divided into two regions, namely, the fullwave region and the PO region. In the fullwave region, the IE is modified by coupling into the PO contribution. Similar to the fast IE method, the modified impedance matrix is decomposed into the near field couplings and the wellseparated group couplings, respectively. By interpolating the Green’s function, the couplings between two wellseparated groups can be computed using fast Fourier transform (FFT). Due to the PO approximation, the hybrid method utilizes fewer unknowns and requires less solution time than the conventional IEFFT. Finally, the proposed method has proved to be valid by comparing with the EM software FEKO. The method of moments (MoM) has been very popular in solving the electromagnetic problems of 3D structures. However, in the situation that antennas are located near an electrically large platform, the efficiency of the conventional MoM may be lost due to excessive computer requirement. Hybrid method which combines MoM with physical optics (PO) asymptotic method appears to be able to well handle such problems. In this currentbased hybrid analysis, the impedance matrix is modified by coupling into the PO contribution. Each MoM basis function interacts with other MoM basis functions directly and through each PO triangle indirectly. Therefore, it is necessary to have as small a MoM region as possible. Otherwise, calculating the interaction between the MoM and PO regions will lead much longer solution time, which may make the analysis of electrically large problems become prohibitive. Another efficient analysis of the problems can be fast integral equation (IE) methods. Recent advancements of fast multipole method (FMM) and its extension called multilevel fast multipole algorithm (MLFMA) have made significant inroads toward solving realistic largesize problems. However, both the methods strongly depend on the integral kernels. The major drawback makes the application of FMM and MLFMA confined. On the other hand, there is another class of fast IE methods called gridbased approaches, such as precorrectedFFT (pFFT), the adaptive integral method (AIM) [14], and the algorithm of sparsematrix/canonicalgrid (SM/CG). In 2005, the IEFFT algorithm was proposed by Seung Mo Seo and JinFa Lee. This method interpolates the Green’s function on a regular Cartesian grid and is easier to implement than other gridbased approaches. All of these fast IE methods require less storage and lower complexity than the conventional MoM. This paper presents a novel hybrid technique, which combines the IEFFT method with PO method. The surfaces of the platform and antennas are modeled by triangular meshes. Antennas are assigned to be the fullwave region and the platform is chosen as the PO region. Thus the electric field integral equation (EFIE) in which the electric field radiated by the PO current is taken into account can be obtained in the fullwave region. Similar to the conventional IEFFT, the modified impedance matrix is decomposed into the near field couplings and the wellseparated group couplings, respectively. As a result of the Green’s function interpolated on a regular Cartesian grid, the couplings between two wellseparated groups can be computed using FFT. Compared with the conventional IEFFT, the proposed technique needs fewer unknowns and requires less solution time. On the other hand, the method has proved to be valid by comparing with the EM software FEKO.
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