Development of the Microstrip Circulator with a Magnetized Ferrite Sphere in Millimeter Wave Band

In this paper, a novel microstrip circulator with a magnetized ferrite sphere is proposed for various millimeter wave communications. A three-dimensional Finite-Difference Time-Domain (FDTD) approach for the analysis of this ferrite sphere based microstrip circulator is first presented. The electromagnetic fields inside the ferrite junction are calculated using special updating equations derived from the equation of motion of the magnetization vector and Maxwell's curl equations in consistency. Frequency dependent insertion loss, isolation and reflection loss of circulator are calculated over a wide band of frequencies with a single FDTD run. Experimental results at Ka band are presented and compared with theoretical simulations. As a result, a good agreement is found between them.     

CAD of Millimeter Wave Y-Junction Circulators with a Ferrite Sphere

A gradient optimization technique along with a definition of cost function is applied to the CAD of the circulator with a magnetized ferrite sphere for millimeter wave communications. A three-dimensional Finite-Difference Time-Domain (FDTD) approach for the analysis of this ferrite sphere based microstrip circulator is presented. The topology of the structure is enforced at each step of optimization and its physical dimensions are used as optimization variables. The cost function is defined using location of zeros and poles of the circulator's transmission, isolation, and reflection functions. Numerical tests show that the optimization process converges from an arbitrarily selected starting point with the new definition of the cost function.     

微带阵列天线的时域散射特性

本文用时域有限差分方法(FDTD)研究了微带阵列天线的时域散射场,分析了入射脉冲极化方向不同以及入射方向不同时的散射场的分布情况;讨论了时域散射场的时域波形以及频谱与微带阵列天线结构的关系;用散射场分离算法讨论了地板对于微带贴片阵列散射场的影响.研究发现,有限大地板的微带阵列天线的散射场主要是由地板的边沿电流产生的,同时微带贴片阵列的谐振频率与入射脉冲的极化方向有关,因此不同的极化方向对应于不同的散射频谱. 关键词： 时域散射 微带天线 FDTD     

High-gain composite microstrip patch antenna with the near-zero-refractive-index metamaterial

A high-gain rectangular microstrip patch antenna which is covered by a single layer metamaterial (MTM) superstrate with the near zero refractive index is proposed. The refraction of the metamaterial at frequency 3.51 GHz–3.57 GHz is very close to zero. The metamaterial with the near zero refractive index is placed 42 mm above an ordinary rectangular microstrip patch antenna. The effectively zero refractive index behavior of metamaterial superstrate can gather the wave emitted from the microstrip patch antenna and collimate it toward the normal direction of the antenna. The finite element method (FEM) and the finite difference time domain (FDTD) method are used to study the characteristics of this antenna. The results of the two methods indicate that the realized gain of the proposed antenna is increased by more than 6 dB, and the antenna has a flatness high gain in the predicted frequency band, where the proposed MTM is designed to have a near zero index of refraction. Therefore, the high-gain antenna is effectively enhanced based on the near-zero-refractive-index metamaterial.     

垂直极化平行板有界波电磁脉冲模拟器辐射近场的快速估算方法

为快速估算出垂直极化平行板有界波电磁脉冲(EMP)模拟器的时域近场,将散射传递函数法应用于该类型模拟器近场的时域计算中,即对于给定的脉冲源,先寻找有效频谱范围能覆盖该源的高斯脉冲源,并应用时域有限差分(FDTD)方法计算该高斯脉冲源激励时模拟器中测试点场的时域响应,再利用傅里叶变换、系统的传递函数及傅里叶逆变换计算得到给定脉冲源激励时各测试点场的瞬态响应。所得计算结果与直接使用给定脉冲源激励时FDTD方法的计算结果符合较好。所述方法可用于同一模拟器在不同脉冲源激励时辐射近场的快速估算,能大大减少FDTD模拟计算的次数,尤其对于中大型模拟器能有效减少计算时间和内存。     

X波段叠层片式微带铁氧体环行器的设计

采用叠层片式化设计有望实现微波环形器与低温共烧陶瓷(LTCC)技术的结合。借助三维电磁仿真手段设计了一种X波段微带铁氧体环行器,基片采用具有不同饱和磁化强度的旋磁材料构成叠层片式结构。研究结果表明,叠片数目及其饱和磁化强度的搭配对环形器的回波损耗和隔离度特性影响显著,这与叠层结构引入的界面及叠片变化的饱和磁化强度影响了环形器的等效输入电路参数有关。通过优化设计,可以获得具有高回波损耗、高隔离度及低插入损耗等优良性能的器件,但带宽受叠片数目及其饱和磁化强度的搭配影响较小,难以通过优化进行拓展。     

A microstrip resonator filter using sandwich structure

We present results for a compact, multiple gap and multiple pass band microstrip resonator filter. The microstrip resonator filter, consisting of a sandwich substrate with a metallic fractal pattern, shows multiple gaps from 40 MHz to 10 GHz. The transmission characteristics of the microstrip resonator filter show multiple pass bands and stop bands for electromagnetic waves over the microwave frequency range. Experimental observations are in good agreement with the results of finite difference time domain (FDTD) simulations. These properties can be useful in the application in compact microwave circuits, microwave filters, and microwave switches. PACS 84.30.Vn; 84.40.Az; 95.85.Bh     

用二维时域有限差分法分析条形多层波导

为精确分析条形多层波导和多量子阱波导，本文提出了一种以二维时 限差分法为基础的全波数值方法，给出了场分布的色散特性的数值结果，并与矢量有限元法已有的结果作了比较；文中还研究了以二维时域有限差分法为基础的标量近似技术，提出了它的有效性和精度的局限性。     

Numerical Stability Analysis of the Thompson-FDTD Method

The stability criterion for the numerical solutions of two-dimensional Maxwell's equations obtained by the method of difference-Thompson transformation (DTTR) combined with the finite difference time domain (FDTD) method is obtained for the first time.     

粒子模拟中的时偏FDTD算法

给出一种能自动对高频噪声进行过滤的时域有限差分(FDTD)算法,称为时偏FDTD算法.在中心差分FDTD算法的基础上,引入时间偏置和松弛迭代处理,得到该算法的计算公式,并进行稳定性与收敛性分析.通过对相对论磁控管的计算,与中心差分FDTD算法比较,验证了该算法的滤波特性.     

复合介质等效电磁参数的数值研究

利用时域有限差分(FDTD)方法研究了掺杂介质材料等效电磁参数的反演方法.首先用FDTD方法计算掺杂介质的反射、透射系数,然后结合遗传算法和传播矩阵法反演不同掺杂比率的等效电磁参数,得到了等效电磁参数随掺杂比率变化的关系曲线.在复合材料的掺杂比率较低和较高时,等效电磁参数计算公式之间以及数值方法得到的结果比较一致;当掺杂比率处于中间值时,则稍有差别.结果显示用数值方法反演复合材料等效电磁参数具有可行性.     

PML-FDTD法在分析负折射率材料中的应用

将时域有限差分(FDTD)法引入了对负折射率材料物理现象的仿真研究.给出了二维TM波在负折射率材料中的时域差分方程,并且在吸收边界处使用了理想匹配层(PML).为了避免在迭代过程中出现的不稳定现象,在差分方程的推导中引入了Drude模型, 并对Pendry提出的由负折射率材料构成的平板透镜具有的完美成像现象进行了数值仿真验证.由仿真结果发现,完美成像现象只在平板透镜的折射率n=－1时出现,当n≠－1时则会出现近轴聚焦效应.     

LED光学传播的有限元研究

有限时域差分(FDTD)广泛应用于提高发光二极管(LED)芯片外量子效率.这种方法是针对波导结构的一种分析计算,对于激光器是有效的,但是对LED很难模拟其有源层多种模式出射的情况.应用有限元电磁场分析方法对LED进行光学建模并对光子晶体结构的外量子效率进行了计算.特别在对光源的处理上,使用了点光源球面波来进行分析并且考...     

Mie scattering calculation by FDTD employing a modified Debye model for Gold material

The parameters calculation for the modified Debye model in the electromagnetic finite difference time domain (FDTD) method is discussed. Validation for the selected parameters is done comparing the FDTD results with the Mie analytical solutions of a gold nanometer sphere under an optical plane wave incidence. Good agreement with an average relative error 6.7% has been demonstrated as to total electrical field amplitudes on the surface of the gold sphere. It indicates FDTD could be adopted in the optical region for a material even with a negative real relative permittivity particularly as metals.     

一种有损非均匀传输线时域分析方法

提出利用等效电路法解决电磁脉冲注入下有损非均匀传输线及其网络端接非线性负载的时域响应问题。采用分段逼近级联方法建立了有损非均匀传输线的等效电路模型。利用设计的快沿电磁脉冲源对有损非均匀微带线端接电阻、瞬态抑制二极管的响应进行了试验和仿真对比分析,验证了该等效电路模型的正确性和解决非线性负载响应问题上的有效性。通过与FDTD法对更复杂的有损非均匀传输线、不等长有损非均匀传输线、有损非均匀传输线网络的仿真结果和计算机运行时间进行对比分析,进一步验证了该等效电路法的正确性以及在解决有损非均匀传输线问题上的普遍适用性和高效性。     

Complete analysis of photonic crystal fibers by full-vectorial 2D-FDTD method

In this paper, an extended finite difference time domain (FDTD) algorithm for the full-vectorial analysis of photonic crystal fibers has been derived. For achieving a good convergence and high accuracy, a kind of modified conformal FDTD method has been applied. An anisotropic perfectly matched layer for truncation of boundary conditions has been introduced. Material and chromatic dispersions are numerically investigated for the photonic crystal fibers with different dimensions and geometrical parameters and different dispersion behaviors are exhibited.     

Calculation of Dispersion Characteristics of a Circular Waveguide with Deep Helical Corrugation by the FDTD Method

We study the dispersion characteristics of a circular waveguide with helical corrugation, which are used in microwave amplifiers and oscillators. The results of calculations by the finite difference time domain (FDTD) method are compared with the results obtained using the perturbation theory and the experimental results. The problems of improving the calculation accuracy are considered     

FDTD Method in the Analysis of Lithium Niobate Modulator

The Mach-Zehnder traveling-wave lithium niobate modulator is simulated by time domain finite difference (FDTD)method for different device geometry. The result is comparable to the reported value by finite element method.     

周期对称结构R-FDTD方法及其减元优化

论述减缩时域有限差分方法(R-FDTD)中暂存场分量边值补充计算的必要性,提出周期对称结构R-FDTD方法,基于对称关系和周期边界条件(PBC),给出需要补充计算的暂存分量表达式.利用对称性,将计算空间缩减为原来的1/4,对称面外侧场分量由对称关系得到,1/4空间周期对称结构R-FDTD可更进一步将计算区域的内存使用量降为FDTD算法的1/6,且不影响计算精度.计算无限大钢筋网和钢筋混凝土墙壁的电磁脉冲响应,结果与FDTD的计算结果吻合.改进的算法在内存使用和计算时间上具有明显的优势.     

FDTD结合DFT分析宽频高功率微波大气传播

联立麦克斯韦方程与电子流体方程,用时域有限差分法(FDTD)模拟高斯型和阻尼正弦型等宽频高功率微波(HPM)的大气传播.在每个时间网格上,根据窄带脉冲的电子速度,通过离散傅立叶变换(DFT)方法求解出宽频脉冲的等效电场,将等效电场和压强代入电离参数公式,使电离参数随空间网格不断更新,提高计算准确性.结果表明,宽频HPM脉冲幅值、脉宽以及海拔高度等参数对大气击穿有明显的影响;大气击穿导致尾蚀效应;随着传播距离的增加,宽频HPM脉冲的尾部衰减加剧,脉宽缩短,引起宽频脉冲的频谱出现展宽、分裂及中心频率移动等现象.