【作者】 汤一铭；

【导师】 吴文；

【作者基本信息】 南京理工大学 ， 电子科学与技术， 2009， 博士

【摘要】 电磁带隙(EBG,Electromagnetic Band-Gap)波导通过对波导腔体进行金属EBG膜片加载形成。它同时具有EBG结构紧凑、禁带特性、带隙外慢波效应的特点以及腔体结构传输损耗小、功率容量大的优点,因此在微波毫米波中大功率系统、元器件及其小型化设计领域具有十分广泛的应用前景。本文对EBG加载波导的电磁特性及其在微波滤波器和喇叭天线设计中的应用进行研究,具体工作如下:(1)采用模式匹配技术(MMT)对四脊方波导的双面不连续性进行分析,得到了四脊方波导的本征值、截止频率、特性阻抗、单模工作带宽等特性与结构尺寸之间的关系。在此基础上采用多层感知器神经网络(MLPNN)模型对四脊方波导的双面不连续性进行建模。MLPNN模型的计算精度与磁场积分方程法(MFIE)、有限元法(FEM)等方法相当,而计算速度大大提高,为EBG波导滤波器的快速设计奠定基础。(2)针对EBG膜片阵列双排平行加载波导带通滤波器(BPF)的设计,分析了膜片高度、加载周期、平行间距等结构参数对频响特性的影响,在此基础上设计了中心频率为9GHz的BPF。测量结果表明本文所设计的BPF通带范围为6GHz～12GHz,通带内插入衰减小于1dB,阻带上边界频率由单排加载情形的14.2GHz提高到16GHz,阻带衰减最大值达到55dB。与单排EBG加载波导BPF相比,阻带带宽和衰减均得到提高,可用于带外杂波抑制。(3)采用EBG膜片阵列对称周期加载的方法,设计了双极化EBG加载方波导BPF。在分析膜片高度和加载周期对BPF频响特性影响的基础上,研制了中心频率为10.6GHz的BPF。测量结果表明,该滤波器通带范围7.5GHz～14GHz,带内插入衰减小于1dB,阻带范围14.5GHz～16.8GHz,阻带衰减最大值达到45dB,双正交线极化隔离度大于25dB,可用于双极化系统中的电路抗干扰。(4)采用EBG膜片阵列对称加载的方法,设计了EBG加载方形棱锥喇叭天线。与普通无加载喇叭、对称四脊加载喇叭的天线性能进行比较分析,结果表明对棱锥喇叭进行EBG膜片阵列对称加载,在相同外形尺寸的前提下,可以获得比普通无加载喇叭更低的旁瓣、比四脊喇叭更高的方向性。在此基础上研制了中心频率为12GHz的EBG膜片加载棱锥喇叭天线。测试结果表明,在10GHz～14GHz频带上天线的方向性系数大于13dB,E面方向图第一旁瓣电平比主瓣低17dB以上,双正交线极化隔离度及工作主模与其它模式的模式隔离度均高于40dB。(5)设计了多过渡段结构的微波宽带同轴-波导转换器,实现低阻抗同轴线-高阻抗波导的宽频转换,用于本文研制的EBG膜片加载BPF和喇叭天线的测试。更多还原

【Abstract】 EBG loaded waveguides are generally synthesized by loading metal EBG planes in waveguide housings. They possess the similar properties to the periodical photon crystals, such as compact physical configurations, stable pass-band/stop-band characteristics, good slow-wave effect on out-band of band-gap. On the other hand, they take the advantages of good mechanical intensity, large power capacity and small transmission attenuation as well as those of the traditional waveguides. Therefore, EBG-loaded waveguides can be well applied in the design of high powered systems, components and their miniaturization at microwave band. This dissertation focuses on the electro-magnetic characteristics of EBG-loaded waveguides and their applications in broadband filters and antennas designs with detailed considerations as follows.(1) The classical Mode-Matching Technology (MMT) is adopted to establish a model of dual-plane discontinuousness of the quadruple-ridged square waveguide, with which the characteristics parameters of quadruple-ridged square waveguide, such as eigenvalues, cutoff frequency, characteristic impedance, single-mode operation band and complex propagation constant, can be accurately obtained. Then Multilayer Perceptron Neural Network Model (MLPNN) and Back Propagation Algorithm (BP) are employed to improve the design efficiency. Corresponding results in this dissertation show good agreement with those deduced by MFIE, FEM in existing references. The model provides theoretical foundation for the design of the EBG loaded waveguide filters.(2) Double-array-loading in parallel is adopted to achieve apparent improvement of the stop-band characteristics referring to those of traditional single-array EBG loaded waveguide BPF. Generalized scattering matrix, equivalent circuit analysis and software simulation are employed to perform parametric optimization. Variation rules of BPF performances have been acquired with various structural parameters, such as inserts height, loading period and parallel distance. An EBG-loaded BPF with center frequency of 9GHz is fabricated. Measured results show 6GHz～12GHz pass-band with in-band insert attenuation less than 1dB and 12.5GHz～16GHz stop-band with the largest out-band attenuation 55dB has been obtained. The filter can be used for out-band high-ordered harmonic suppression.(3) Regarding the symmetrical structure and dual-polarization trait of regular square waveguide, a symmetrically quadruple-loaded BPF is designed. Influences of inserts height and loading period on the overall BPF characteristics are considered. The inserts shape is chose to be round-crown and rectangular-bottom, which can reduce the EM coupling between the two sets of distributed LC resonant planes in perpendicular position. An experimental filter is designed and measured results show good agreement with the predicted results. 7.5GHz～14GHz pass-band with insert attenuation less than 1dB and 14.5GHz～16.8GHz stop-band with largest out-band attenuation 45dB can be obtained. Good dual-polarization isolation, larger than 25dB, is achieved on the entire band. The BPF can be used for the high-ordered harmonic suppression of dual-polarized systems.(4) An EBG loaded square pyramidical horn antenna is designed to improve the performances of ordinary unloaded horn. Simulations of ordinary unloaded horn, symmetrically quadruple-ridged horn and EBG-plane symmetrically loaded horn are performed to compare their characteristics of return loss, modal isolation, E-plane and H-plane radiation patterns. A practical EBG loaded horn is fabricated and the measured results show good agreement with the predicted ones. On the condition of same dimensions, EBG-loaded horn can achieve larger directivity than quadruple-ridged horn and lower side lobes than ordinary unloaded horn.(5) A design of microwave broadband coaxial to waveguide transition is proposed for the measurement of EBG loaded filters and horn antenna. Designs of several components are presented, including the wideband coax to double ridged waveguide transition, double ridged waveguide to arbitrary sized rectangular waveguide transition, rectangular-square waveguide transition. Double ridged waveguides are used to obtain lower cutoff frequency and better impedance matching with standard coaxial 50Ω. Tapered waveguide and ridges are employed to provide the best transition between different waveguides with different cross-sections. Two sets of microwave broadband measurement loops are established respectively for the measurement of the EBG loaded waveguide BPFs and horn antenna.更多还原