各类复杂情形下的电磁特性预估与分析一直是计算电磁学中的重要研究课题，该类问题通常具有电尺寸大、几何外形复杂、难以开展实验测量、难以获取真实电磁参数等特点，但又极具工程应用价值，因此得到了许多学者的广泛关注。计算电磁学中的高频近似方法因其计算效率高，消耗计算资源少，在研究此类问题时相比低频数值方法具有更多优势。本文以经典高频方法——弹跳射线法为主要算法，对微波暗室、飞机目标、大型油库等复杂情形下的目标电磁特性进行初步计算和分析。文章主要内容如下：

（1）简单介绍了弹跳射线法的基础理论，重点说明了算法中射线管生成、线面求交、射线路径与场强跟踪、远区场积分等关键步骤。介绍了雷达散射截面、雷达一维距离像等常见的表征目标电磁散射特性的物理量。对复杂目标的建模流程，以及MSH格式文件的组织方式进行了说明。最后选取部分典型目标进行计算，验证了算法的正确性。

（2）使用弹跳射线法对微波暗室的指向精度进行初步计算和分析。以某暗室模型为例，介绍了暗室的内部构造，吸波材料贴合情况、发射天线的频率和辐射方向图等计算条件，使用弹跳射线法对若干收发点的反射电平和指向角误差进行了计算，结果表明发射天线频率、收发点位置等因素均会对暗室性能产生影响。

（3）使用弹跳射线法分析某飞机目标的电磁散射特性。计算了某飞机目标分别在空载和挂载炸弹情况下的RCS和雷达一维距离像，结果表明从飞机下方能更好地探测到其挂载情况。另外，在飞机表面涂敷介质材料，对比了涂敷前后的RCS值，结果表明涂敷材料后能够在一定程度上降低雷达回波强度，具体效果与观察角度、入射频率、涂敷材料厚度等因素有关。

（4）使用弹跳射线法计算油库及背景复合目标的电磁散射特性。使用时域方法计算了某大型油库目标不同观察角度下的时域回波，并利用傅里叶变换得到其宽频带内的RCS值，使用频域方法计算单个频点下，不同观察角度时的单站RCS和雷达一维距离像，计算结果表明该复合目标的电磁散射特性随入射角度和频率的不同表现出丰富的变化。

Prediction and analysis of electromagnetic properties in various complex situations has always been a vital research topic in computational electromagnetics. These problems are usually characterized by large electrical size, complex geometry, difficulty in carrying out experimental measurements, and difficulty in obtaining true electromagnetic parameters. The topic has gained wide attention from the academic community because of its great engineering application value. The high frequency approximation method in computational electromagnetism has more advantages than the low frequency numerical method in studying such problems because of its high computational efficiency and less computational resources. This paper mainly uses the classical high-frequency method—The shooting and Bouncing Ray(SBR) to calculate and analyze the targets’ electromagnetic characteristics in complex situations such as microwave anechoic chamber, aircraft target and large oil depot. The main contents of thesis are as follows:

 

(1) The basic theory of Shooting and Bouncing Ray is briefly introducedwith emphasis on the key steps, for instance:ray tube generation, line intersection, ray path and field strength tracking, and far field integration. Then the common physical quantities that characterize the target’s electromagnetic scattering characteristics (radar cross section and radar one-dimensional range profile etc.) are presented in the paper.The modeling process for complex objects and the organization of MSH format files are further elaborated. Finally, the author sorts out some typical targets for calculation to verify the accuracy of the algorithm.

 

(2) Preliminary calculation and analysis of the pointing accuracy of the microwave anechoic chamber are conducted by using Shooting and Bouncing Ray. Taking the microwave anechoic chamber model as an example, the author expounds internal structure of the darkroom, the fitting of absorbing materials andthe frequency and radiation pattern of the transmitting antenna etc.. Then the reflection level and the pointing angle errors of several transmit-receive points are calculated by SBR. The results show that the frequency of the transmitting antenna and the position of the transmit-receive points both affect the performance of the microwave anechoic chamber.

 

(3) Based on the author’s analysis of the electromagnetic scattering characteristic for an aircraft target by using SBR. Then RCS and radar range profiles of an airplane target are calculated respectively in no-loading and mounting situations. The results show that the mounting situation can be better detected from the bottom of airplane. In addition, The RCS values before and after coating are compared by the author. The results reveal that the RCS values after coating can reduce the radar echo intensity to a certain extent. The specific effect is related to the observation angle, incidence frequency, coating material thickness and other factors.

 

(4) The electromagnetic scattering characteristics of fuel depot and background combinative objects are calculated by Shooting and Bouncing Ray. By using the time domain method ,the author calculates the time-domain echoes of a large fule reservoir target from different observation angles, and the RCS values in the broadband are using the Fourier transform. In addition, the frequency-domain method is utilized for the calculations of the single-station RCS and the one-dimensional range profile of radar from different observation perspectives under a single frequency. The calculationresults demonstrate that the electromagnetic scattering characteristics of the composite target vary abundantlywith the incident angle and frequency.

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