【作者】 孟东林；

【导师】 沙斐；

【作者基本信息】 北京交通大学 ， 交通信息工程及控制， 2008， 博士

【摘要】 作为电磁辐射类测试场地代表的混响室和电波暗室都受限于低频性能,而采用射线追踪等方法在低频时分析的误差又较大。因此本文专注于研究二者的低频性能。首先,针对当前最新并且具有众多优点的固有混响室IRC,从基本混响理论、几何外形和散射器三个方面进行了研究:首次推导出了有源圆柱腔体中不仅物理意义清晰而且方便应用的电磁场解析式;扩展了采用本征函数叠加法得到的关于三维有源矩形腔体的有关理论的应用范围;详细地研究了不同几何腔体中的模密度和模结构;目的是通过深入研究混响室的工作机理,为寻求最优的混响室几何外形提供坚实的理论基础。这是本文最主要的创新成果。采用全波分析仿真的结果表明,在圆柱体、长方体、三棱柱和楔台这四种腔体中,在不同频段各有优缺点;就获取低频均匀性的能力而言,楔台腔体的总体效果最优。对散射器的研究发现,与Schroeder散射器相比,特定尺寸的球冠作为散射器更能改进低频场均匀性,而且对混响室没有明显的加载,即不会显著降低其0值。特定尺寸的球冠有望成为最有前途的散射器。这是本文另一主要创新成果。上述研究,为开发IRC指明了希望和思路;更重要的是,所得结论可用于改进机械搅拌混响室和电子模搅拌混响室的低频性能。其次,提出了一种改进的混响室低频段品质因数Q的时域估测方法。这种方法非常适合工程应用。再次,提出一种能准确计算各种射频吸波体反射率的全波分析方法,并针对各种吸波材料做了系统研究。这些分析方法和结果可直接用于吸波体的优化和生产。最后,研究如何采用全波分析方法来预测电波暗室的低频性能;并且用于研究影响电波暗室性能的关键因素。更多还原

【Abstract】 Both as typical radiation test sites, the performances of Reverberation Chamber (RC) and Anechoic Chamber (AC) at low frequency are deteriorated, which cannot be predicted accurately by ray-tracing method and so on. Therefore, this thesis focuses on this problem.A systematic study is made on the basic reverberating theory, geometrical shapes of RC and diffusers, in order to develop intrinsic reverberation chamber, which has lots of advantages over mechanical-stirring reverberation chamber.1) Expressions for electromagnetic fields in various regular cavities are deduced. An original expression is derived analytically for the electromagnetic field in current-active cylindrical cavity, and the expression is very convenient for application; the singularity, in the formula of reference [107] for 3D current-active rectangular cavity, is resolved. The mode density, as well as mode structure in diverse cavities is studied, too. These studies lay a theoretical foundation for optimizing the geometrical shape of RCs.2) Since it is very difficult to deduce electromagnetic formulae for irregular or asymetrical cavities, two numerical methods are adopted to study the effects of different geometrical shape of RCs on the field uniformity (FU), under the guidance of above mode density theory. The simulation results show that "truncated wedge" overmatch other shapes of chambers in acquiring better FU.3) The effects of different diffusers/diffractors on the FU are studied. The mode density theory, as well as simulation results shows that specific ball crowns (SBCs) are superior to other planar diffusers/diffractors, such as Schroeder diffusers/diffractors, because the FU improvement from SBC is more remarkable, and what’s more, SBCs will not load the RC notably.The above findings show a way to IRC (Intrinsic Reververation Chamber); what’s more important, the findings are useful to improve the performances of MSRC (Mechanical Stirring Reverberation Chamber) and EMSRC (Electronic Mode Stirring Reveration Chamber) at low frequency.Then, an improvement is made for time-domain method to evaluate rapidly the quality factor of RCs, which is good for industrial test.The second part of this thesis focuses on the problems of AC. First, an efficient method is put forward to calculate accurately the reflectivity of radio-frequency (RF) absorbers. These conclusions can be a good guide for manufacturing absorbers.The effects of RF-absorbers on the floor, on long-side-wall and on short-side-wall, on the performance of ACs are studied by Finite Element Method, with regard to the relation between sizes of shielding enclosure, the height of RF-absorbers and the incident angle. The cause of disputation occurred during radiation immunity test is illustrated visually by three-dimensional graph in the zone of EUT. The key RF-absorbers in AC area also found by comparing the effects of absorbers on different side walls. Such full-wave analysis method is valuable that the performance of a specific AC can be predicted accurately before practical construction.更多还原