【作者】 邹艳林；

【导师】 刘其中；

【作者基本信息】 西安电子科技大学 ， 电磁场与微波技术， 2007， 博士

【摘要】 随着军用电子技术的飞速发展,现代战争对飞机与导弹精确制导的要求也越来越高。机载、弹载天线外部的天线罩,在对天线进行物理保护的同时,也会在一定程度上影响天线的电磁性能,因而对天线-天线罩一体化系统进行精确的电磁分析不仅具有理论意义,而且具有国防应用价值。由于机载、弹载天线罩电尺寸很大,对其进行精确分析往往需要通过并行计算或在大型工作站上进行。考虑到大部分机载、弹载天线罩具有旋转对称的结构特性,我们可以利用这种结构上的特殊性降低计算需求。本文密切结合国防重点项目“天线-天线罩系统电磁特性一体化分析”,利用天线罩结构上的旋转对称特性,并通过一系列的改进措施,实现了在个人计算机上对电大尺寸天线-天线罩系统的快速精确分析。本文针对旋转体天线罩分析中的几个关键环节和难点问题展开研究,作者的主要工作和成果可以概括为：1.研究了基于表面积分方程的天线-旋转体天线罩的建模方法。针对天线罩底部封闭和不封闭两种情况,基于等效原理建立了两种等效模型,然后分别从两种等效模型出发,给出了表面积分方程建立的原理和过程以及矩量法矩阵方程建立的详细过程。为了利用矩量法的准确性并且降低计算需求量,对采用MoM-PO混合方法对旋转体天线罩建模也作了研究。2.研究了快速计算入射场模式分解系数的方法。通过抽样,将天线罩表面上沿方位角方向周期分布的入射场由空域连续信号转化为空域离散信号,进而将傅立叶级数转化为离散周期序列的傅立叶级数,从而可以通过快速傅立叶变换一次计算出特定环面上所有模式下的入射场模式分解系数,避免了传统的采用积分方法计算时每个模式下需要单独计算所导致的入射场模式分解系数计算时间过长的问题。3.提出了有效选取最小计算模式数的方法。对于旋转体目标分析中所采用的基于模式分解的矩量法,计算时间几乎与计算模式数成正比。模式数取得过少,计算结果尚未收敛；模式数取得过多,造成不必要的计算时间浪费。基于Parseval定理,本文提出通过引入能量谱图和平均能量系数来快速准确确定最小计算模式数,剔除不必要的计算,在保证计算结果收敛的前提下使计算量最小4.在天线罩表面的局部曲线坐标系下,对阻抗矩阵元素的计算进行了研究。从所建立的电磁场表面积分方程出发,经过细致的推导,给出了阻抗矩阵元素的计算表达式。将沿母线方向的三角形函数采用四段脉冲函数来近似,避免了沿母线方向的积分运算；当检验点和源点重合时,采用加一个微扰量的方法来避开奇异性问题,避免了矩阵元素计算中繁琐的奇异性处理过程。5.充分挖掘阻抗矩阵的特性,利用阻抗矩阵的对称性、正负模式之间矩阵元素的对应关系以及基函数的部分重叠性等几个方面的特点,提出了一系列改进措施,极大地减少了计算量,节约了内存需求。6.提出了针对天线-旋转体天线罩一体化系统的远场方向图的快速计算方法。分别介绍了采用直接积分和利用互易定理的两种远场计算方法,在两种方法下,均对方位角积分进行了解析处理,从而能够实现远场的快速计算。7.提出了当分析天线在罩内的扫描特性时,利用不同扫描角度下阻抗矩阵相同这一特点,在每个模式下共用阻抗矩阵的逆矩阵,同时计算所有角度的等效电磁流系数。这样就避免了不同扫描角度下阻抗矩阵的填充和求逆过程的反复执行,极大地减少了计算量。对某大型阵列天线在天线罩内的扫描特性进行了分析,给出了在天线罩影响下天线的主瓣衰减及瞄准误差等特性。更多还原

【Abstract】 With the rapid development of the military electronic technology, the modern warfare puts forward more and more requirements to the precision guidance of aircraft and missile. The airborne radome is necessary for providing physical protection to the antenna, but at the same time it affects the electromagnetic properties of the antenna to a certain extent. Therefore, the accurate electromagnetic analysis to the antenna-radome integration system is not only of theoretical significance, but also of national defense application value. Due to the electrically large size of the airborne radome, the accurate analysis to it is usually carried out through parallel computing or on a large workstation. Considering that most of the airborne radomes have the rotationally symmetric structure property, we can reduce the computational requirements by taking advantage of this property. Closely associated with the defense project, by utilizing the structure property of the radome and making a series of improvements, we realize the fast and accurate analysis of the electrically large antenna-radome integration system on the personal computer. Aiming at the key and difficult problems met in the analysis of the body of revolution radome, this dissertation makes in-depth research. The author’s major contributions are as follows:1. The modeling method based on the surface integral equation is presented to model the antenna-radome integration system. For the two cases that the radome bottom closes and uncloses, two equivalent models are established based on the equivalence principle. Then from these two models, the principle and process are presented in detail that how the surface integral equations and the moment-method matrix are established. In order to retain the accuracy of the method of moments (MoM) and reduce the computational requirements, a modeling technique based on the hybrid method of moments-physical optics (MoM-PO) is also introduced.2. A method to fast calculate the mode decomposition coefficients of the incident field is presented. By sampling, the incident field that is periodically distributed along the azimuthal direction on the radome surface is then transferred from continuous-space signal to discrete-space signal. Correspondingly, the Fourier Transform is translated into the discrete Fourier Transform, which can be performed by the Fast Fourier Transform (FFT). All modes’decomposed coefficients of a field component on a certain segment can be obtained with one FFT computation. It avoids the too long computing time caused by the individual computing under every mode when the conventional integral method is used.3. A method is presented to efficiently select the minimum number of calculated modes. For the MoM based on the mode decomposition technique, which is adopted in the analysis of the rotationally symmetric object, the computation time is proportional to the number of modes that MoM processes. On the one hand, if the number is too small, the computing result will not reach convergence. On the other hand, if the number is too large, it will cause unnecessary computation. Based on the Parseval theorem and by introducing the energy spectrum graphs and the average energy coefficients, a method to fast and accurately determine the minimum calculated mode number is introduced. It will alleviate unnecessary computation burden and save a lot of time.4. Under the local curvilinear coordinate system of the radome surface, the computing of the impedance matrix elements is introduced. Starting from the established electromagnetic surface integral equations and through detailed derivations, the computing expressions of the impedance matrix elements are presented. In order to avoid the integration of the arc length, every triangular function along the generatrix is approximated as four subsection pulse functions. By adding a perturbation, the fussy singularity processes in the computing of the matrix elements are avoided when the test point and the source point are superposed.5. The characteristics of the impedance matrix are distilled, such as the symmetry of the matrix, the correspondence between the matrix elements of the positive modes and that of the relative negative modes, and the superposition of the basis functions. By utilizing these characteristics, a series of improvements are made to reduce the computation and memory requirements extremely.6. A method is presented for the fast calculation of the far-field pattern of the antenna covered by the body of revolution radome. Two far-field calculating methods that directly by the surface integration and by the reciprocity theorem are introduced respectively. In both methods, the integrals with respect to the azimuthal angle are carried out in closed forms so that it’s easily to calculate the far-field pattern fast and exactly.7. When the scanning property of the antenna-radome integration system is analyzed, the sameness of the impedance matrix for various scanning angles can be utilized. Under every calculated mode, the equivalent current coefficients for all the scanning angles are calculated simultaneously to share the inverse of the impedance matrix, thus the processes of filling the impedance matrix and getting its inverse needn’t to be carried out repeatedly for various scanning angles. As an example, the scanning property of a large array antenna in the presence of a radome is analyzed and some parameters are calculated, such as the attenuation of the main lobe and the boresight error.更多还原