The analysis of the target's broadband electromagnetic scattering characteristics plays an important role in radar stealth and recognition areas. The traditional method of moments (MoM) needs to calculate the currents at each frequency point when analyzing the target. With the increase of the target electrical size and complexity, the radar cross section (RCS) of the target changes drastically with frequency, it is necessary to calculate the accurate frequency response with a small frequency interval, which is very time-consuming in calculation and not feasible. This paper proposes to combine the subdomain method of moments (SMoM) with the Chebyshev approximation technique (CAT) to efficiently analyze the electromagnetic scattering of arbitrary shaped objects over a broad frequency band. In the SMoM technique, the whole object can be divided into several regions, each of which can be independently solved by the method of moments (MoM). The CAT technique is employed to expand the unknown current coefficients into a Chebyshev series for achieving fast frequency sweeping. Instead of direct point-by-point simulations, it is only necessary to calculate the currents by SMoM at several Chebyshev-Gauss frequency sample points. Furthermore, the Chebyshev series are matched via the Maehly approximation to a rational function to improve the accuracy. Numerical examples show that the hybrid technique can greatly reduce the computation time without loss of accuracy.
© 2013 IEEE.

飞机等电大尺寸平台上装载着各种用途如通信、导航、探测目标的天线，因此多天线系统的电磁兼容性(EMC)分析一直是现代电磁工程中的难点课题之一。为了实现良好的兼容性，并使天线的性能得到正常发挥，机载多天线系统的电磁兼容性(EMC)分析成为了机载天线设计关键技术里的重中之重。本项目深入研究了高效的电磁算法，并将其用于目标电磁散射分析以及机载多天线系统的辐射特性分析中。本项目在以下几个方面取得重要进展和成果:(1)研究了基于区域分解的矩量法(MoM)和自适应积分算法(AIM),对每个子区域可独立求解，通过强加边界条件保证电流的连续性，利用迭代求解每个子区域上的表面电流从而高效求解得到整个目标上的电流密度。(2)发展了高效快速扫频技术，针对传统AIM和AIM-PO需要逐个频点求解积分方程消耗大量时间的问题，通过将切比雪夫逼近引入AIM-PO以及将渐进波形估计技术引入基于线面连接的AIM中，实现了机载天线宽带特性的高效计算。(3)开发了高阶矩量法与多层快速多极子的混合算法，将介质阵列天线区域采用高阶矩量法求解，平台采用多层快速多极子分析，通过考虑他们之间的耦合，利用迭代算法求解整个区域上的感应电流和感应磁流，从而可高效分析机载阵列天线的辐射特性。(4)研究出基于多天线系统的高低频混合算法，将每一个天线及其附近区域划分为MoM区域，平台划分为PO区域，通过考虑多个MoM区域之间的耦合以及MoM区域与PO区域之间的耦合，利用迭代算法求解多个MoM区域和PO区域上的表面电流，进而得到机载多天线系统的辐射特性。

A microstrip-fed slot antenna with dual rejection bands is designed and prototyped for ultrawideband (UWB) applications. The rejection band for WiMAX is achieved by symmetrical etching a pair of nested four-Arm spiral slots on the ground plane. Selfinterdigital electromagnetic band-gap (EBG) structures are embedded to create other rejection bands for WLAN and are placed on both sides of the gradient T-shaped microstrip-fed. The simulated result and measurement data show that the antenna impedance bandwidth (Voltage Standing Wave Ratio is less than 2) covers the entire UWB bandwidth range with two eliminated bands of 3.22-3.81 GHz (0.59 GHz, 16.7%) and 5.11- 5.84 GHz (0.73 GHz, 13.4%). In addition, the designed antenna achieves a stable gain and exhibits omnidirectional radiation patterns except at rejection frequency bands, which makes it a suitable candidate for UWB applications that will not be interfered by WiMAX/WLAN systems.
© ACES.

A microstrip-fed slot antenna with dual rejection bands is designed and prototyped for ultra-wideband (UWB) applications. The rejection band for WiMAX is achieved by symmetrical etching a pair of nested four-arm spiral slots on the ground plane. Selfinterdigital electromagnetic band-gap (EBG) structures are embedded to create other rejection bands for WLAN and are placed on both sides of the gradient T-shaped microstrip-fed. The simulated result and measurement data show that the antenna impedance bandwidth (Voltage Standing Wave Ratio is less than 2) covers the entire UWB bandwidth range with two eliminated bands of 3.22-3.81 GHz (0.59 GHz, 16.7%) and 5.11-5.84 GHz (0.73 GHz, 13.4%). In addition, the designed antenna achieves a stable gain and exhibits omnidirectional radiation patterns except at rejection frequency bands, which makes it a suitable candidate for UWB applications that will not be interfered by WiMAX/WLAN systems.

Experimental results reported in many literature have demonstrated that an antenna array should have two or more grating lobes in its scattering pattern; however, it is not clear how these grating lobes occur and vary. In this paper, we propose a new method to predict the number and location of scattering grating lobes generated by an array antenna. In the proposed method, the radar cross section (RCS) of array antenna can be decomposed into multiplication of the array RCS factor and the element RCS factor. The array RCS factor bears universal applicability so that it can be used to directly determine scattering properties of array antenna. Compared with the full-wave simulation techniques, the new method requires much less computation time and memory storage so that it is more suitable to be employed as the basis of a synthesis method to predict the desired RCS pattern of a large array antenna. As examples, the scattering properties of the dipole antenna arrays are investigated to validate the new method, numerical results demonstrate that the number and location of scattering grating lobes predicted by using the proposed method coincide with those simulated by using a MoM based commercial; software FEKO.
© ACES.

The PMCHWT-IE-FFT-BURA is applied to the wideband analysis of electromagnetic scattering property of homogeneous targets. Over the broad frequency band, the fast computation is achieved by the Maehly expansion on the basis of the Chebyshev approximation of the electric and magnetic currents. On the Chebyshev sampling points, PMCHWT-IE-FFT greatly reduces the memory requirement by sparsely storing the impedance matrix and decreases the computational time to the greatest degree by block acceleration of the matrix-vector product. Finally, numerical results show that the proposed method can make efficient analysis of wideband property of homogeneous targets without sacrificing accuracy much .
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