平面螺旋带线谐振器谐振频率的计算

提出了一个用来模拟、分析和计算平面螺旋带线谐振器谐振频率的物理模型和方法。借助该模型，采用矩量法计算了螺旋带线上的电荷分布，进行计算出平面螺旋带线谐振器的分布电容，从而得到其等效电路参量并最终计算出谐振频率，计算结果与实验数据十分一致。     

Design of superconducting MRI surface coil by using method of moment

A method of moment with an enhanced model to design high-temperature superconductor (HTS) RF surface coils for magnetic resonant image (MRI) is presented. The resonant frequency and quality factor (Q) of HTS RF spiral coils are simulated using this method. The agreements of resonant frequencies and Qs between the simulation and measurement are excellent with differences less than 1 % and 3 %, respectively. The 0.2-/spl mu/ m-thick YBaCuO (YBCO) thin films are deposited onto single side of 0.508-mm-thick LaAlO/sub 3/ (LAO) and sapphire substrate and patterned into a spiral shape. To accurately analyze the resonant frequency and Q of a coil, an enhanced two-fluid model is employed. HTS RF coils with diameter of 65 mm for 0.2 T and 1.5 T MRI systems are designed and fabricated with the measured Q of 19 K and 23 K, respectively. In addition, the shift of resonant frequency due to the mutual coupling between two HTS spiral coils is predicted by this method, which is important for design of HTS coil arrays in an MRI system.     

圆形螺旋线圈自感和分布电容的计算

提出了一种计算圆形螺旋线圈自感和分布电容的方法。在元件尺寸小于波长的准静态近似情况下用 Sommerfeld类型积分计算小段平面圆弧的自感和互感 ,然后用螺旋线方程对每一小段圆弧的自感和圆弧间的互感积分 ,算得螺旋线圈的自感。计算螺旋线圈分布电容时同样先计算出两小段同心圆弧间的电容 ,然后用螺旋线方程对其积分算得螺旋线圈的总分布电容。编制了相应的程序对多种情况下的螺旋线圈自感和分布电容进行了计算 ,计算与实验结果比较 ,有较好的一致性。与经验公式相比 ,计算自感的方法有更广的适用范围和对实验结果更好的逼近。而分布电容的计算方法比其它的方法大大减少了运算量。     

Miniaturization of wide-band VHF filters by using spiral resonators

The miniaturization of a wide-band VHF filter composed of distributed resonators has been studied. The miniaturized filter was realized with spiral resonant lines and lumped capacitors. The filter was designed using a prototype filter circuit composed of only series-resonant lumped-constant circuits. Each resonant circuit is transformed to another resonant circuit consisting of a spiral resonant line and two capacitors. One capacitor is connected to each end of the spiral resonant line. With this technique, the line length becomes very short, e.g., one-twentieth wavelength, in comparison with the line length in conventional resonant lines of one-half or one-quarter wavelength. A filter which has a 160-185 MHz passband and a volume of 3 × 4 × 10 cm³was realized with 10 spiral resonators. The filter exhibits superior characteristics with very little volume.     

A Quick Accurate Method to Measure the Dielectric Constant of Microwave Integrated-Circuit Substrates (Short Papers)

A technique is described that makes possible the accurate measurement of the dielectric constant of microwave integrated-circuit substrates. The substrate is metallized on all sides, hence forming a tiny resonant cavity, and the resonant frequencies are determined either from transmission or reflection. The dielectric constant is then calculated to an accuracy of better than 1 percent.     

Numerical solution of higher order mode cutoff frequencies inasymmetric TEM cells by Galerkin method

The authors describe a Galerkin method (GM), which determines efficiently the basis functions satisfying the edge conditions and the size of the elements on the Neumann boundaries in this paper. The calculated higher order mode cutoff frequencies in both symmetric and asymmetric TEM cells by the GM are presented. The authors could then solve the technical debate for TE₁₂-, TE₀₃-, TM ₁₁-, and TM₁₂-mode cutoff frequencies in the symmetric TEM cell. It is also shown that the measured resonant frequencies of a designed asymmetric TEM cell agree well with the predicted data by the GM     

垫片加载圆柱介质谐振器的谐振频率计算方法

本文利用开波导法对有垫片加载的圆柱型介质谐振器之谐振频率进行了计算,其计算结果与实验吻合，误差小于1％。此方法适宜于实际工程。     

Resonance in a superstrate-loaded cylindrical-rectangularmicrostrip structure

The complex resonant frequencies of the cylindrical-rectangular microstrip structure loaded with a dielectric superstrate layer is studied using a rigorous full-wave analysis, and the numerical results are obtained using the Galerkin moment method calculation. The numerical convergence for the selected sinusoidal basis functions with and without the edge singularity condition is also discussed. Numerical results for the dependence of the real and imaginary parts of the complex resonant frequencies on the superstrate permittivity and thickness are calculated and analyzed, and are compared with those obtained for the planar microstrip structure     

Dielectric ring-gap resonator for application in MMIC's

A dielectric resonator, the dielectric ring-gap resonator, is introduced and analyzed. The dielectric ring-gap resonator is obtained by sawing a narrow gap into a dielectric resonator. Resonant frequencies and unloaded Q-factors of quasi-TE_0pq mode in the ring-gap resonator have been calculated by an appropriate equivalent circuit starting from the resonant frequencies and the field distributions of the TE_0pq modes in the ring resonator. The calculated resonant frequencies of the fundamental quasi-TE₀₁₁ mode show an accuracy of <1% compared with the experimental results. Coupling techniques to couple the ring-gap resonator to a microstrip line on a thin substrate, using the electric fringing field near the gap, have been experimentally investigated. A rigorous method for determining resonant frequencies and field distributions of TE modes in a multicomposite multilayered cylindrical resonator is presented. This resonator consists of numbers of cylinders that are arbitrarily layered in the axial direction     

改进的计算贴片天线谐振频率的变分方法

本文提出一种具有较高精度的计算微带贴片天线谐振特性的变分方法，其主要改进在于用边界导纳计入贴片边缘场和辐射场的效应。文中导出了具有导纳边界的任意形状贴片天线谐振频率的泛函变分表达式，并对不同结构参数的圆形贴片天线进行了数值计算。所得结果与测量值比较表明，误差在１％以下     

Rigorous analysis of shielded cylindrical dielectric resonators bydyadic Green's functions

This paper presents a rigorous approach for the calculation of resonant frequencies of a metallic cavity loaded by a dielectric resonator. Tangential fields at the air-dielectric interface are derived from dyadic Green's functions and boundary conditions are applied. Dyadic Green's identity and the boundary element method are used to solve the numerical problem. In order to validate the method, resonant frequencies are calculated for a cylindrical cavity loaded with a dielectric cylinder and compared with available results in the literature. Then resonance is studied for dielectric cylinder in a rectangular cavity. In the case of multiple dielectric resonators in the cavity, the coupling coefficient is computed with an original method based on the use of symmetries     

Analytical and Experimental Considerations on the Resonant Frequency and the Quality Factor of Dielectric Resonators

A dielectric pillbox resonator placed on a dielectric substrate is analyzed by a new method, the approximate mode matching method, in which the cross section of such a resonator is subdivided into several sub-sections having a simple geometry of the boundaries, i.e., dielectric slab radial waveguides, and the continuity condition of fields between subsections is treated in the least-squares sense. The resonant frequencies and the intrinsic Q values due to the leakage loss through the dielectric substrate calculated by this method are presented together with experimental results obtained in the 50-GHz region. As a result, it is found that the experimental results for both the resonant frequencies and the Q values agree better with our calculated ones than with the results by other approximate method, and so it will be concluded that the analytical method presented here is almost enough to discuss precisely the resonant characteristics of a dielectric pillbox resonator.     

对称L型缺陷微带结构可调带通滤波器研究

设计了一种由对称L型缺陷微带结构实现的新型频率可调带通滤波器,并给出了相应的等效电路;对具有该结构的单频带带通滤波器的S参数频响特性进行了仿真与分析,并计算了耦合系数;依据上述结构设计制作了一种可调谐的双频带带通滤波器,并对其谐振频率的可调性进行了分析。结果表明:所制滤波器的谐振频率分别为2.4 GHz和3.5 GHz,相对带宽分别为4.63%和4.95%,有效电路尺寸仅为26.0 mm×1.2 mm。该L型缺陷微带结构带通滤波器具有结构简单紧凑、尺寸小、频率选择性好和谐振频率独立可调等优点。     

Resonant modes in shielded uniaxial-anisotropic dielectric rodresonators

Rigorous field analysis by the mode-matching method is presented for dielectric rod resonators, including such uniaxial dielectrics as sapphire, which are placed between two parallel conducting plates or in a conducting cavity. The wave equations for E_Z and H_Z in a uniaxial anisotropic dielectric medium are derived in a cylindrical coordinate system. Based on these wave equations, the characteristic equations for the two resonator structures are derived and can be used to calculate the resonant frequencies of any resonant mode. Cutoff conditions of the resonant modes are discussed for parallel-plate-type resonators. Resonant frequencies of some lower order modes are calculated for both types of resonator. Mode charts useful for designing the resonators are presented. It is verified that the mode-matching method used commonly for the analysis of isotropic-dielectric resonators can be applied successfully to uniaxial-dielectric resonators     

Determination of plasma electron-density distribution from the resonant frequencies of a parallel-plate cavity

A microwave resonant cavity method of plasma diagnostics is demonstrated for a parallel-plate cavity containing a cold, collisionless, and isotropic plasma. The method is extended to more general cavities and plasmas in the Appendix. The approach presented here differs from perturbational formulations in that assumptions about the perturbed fields are not made. The analysis gives an exact relation between the electron-density distribution and the resonant frequencies. Laboratory measurements of resonant frequencies then allow a spatially detailed computation of the electron-density distribution. Results are found to agree well with Langmuir probe measurements.     

基于奇异值分解的方法求解目标内谐振时的散射截面

表面积分方程已被广泛地用来分析电磁散射问题,但在离散的内谐振频率点上,用矩量法求解积分方程将得到错误的结果.本文基于电场积分方程,应用奇异值分解找出谐振模电流,并采用正交化方法将其舍去,从而得到非谐振模电流的分布.文中计算了一无限长理想导体圆柱内谐振时的散射截面,所得结果与解析解一致,并对一无限长理想导体三角柱的前向散射截面进行了计算,结果表明本文方法是有效和准确的.     

大的标准TEM小室内谐振频率的计算

本文分别用FD-TD(时域有限差分)法和不均匀划分TLM(传输线矩阵)法计算标准TEM小室的谐振频率。在FD-TD法的计算中,提出一种新的磁边界条件的处理方法,节省了计算量,给出了大量未曾发表过的标准TEM小室内谐振频率的计量结果。在不均匀划分TLM方法的计算中,按小室的自然结构不均匀的划分小室内的传播空间,也达到了节省计算量的目的。最后,对这两种方法和计算结果进行了比较。给出了若干结论。     

Accurate determination of modes in dielectric-loaded cylindricalcavities using a one-dimensional finite element method

A unified approach is presented for calculating the resonant frequencies of all the modes in cylindrical cavities axisymmetrically loaded with dielectrics. In this method, the radial variations of the field components in the resonator are expressed in terms of first-degree finite-element polynomials, whereas the axial variations of the field components are approximated by trigonometric functions. To calculate the resonant frequencies, an H-vector variational formulation is employed and minimized with respect to the coefficients of the expanded field components. Spurious solutions which are inherent in the finite-element technique are effectively eliminated by means of a penalty term included in the variational expression, imposing a divergence-free magnetic field constraint. To show the capability of the method, resonant frequencies of several cylindrical cavities, including those loaded with dielectric rods and dielectric rings, were calculated. A mode chart is presented which can be used for designing certain multimode dielectric-loaded cavity filters. In contrast to other rigorous techniques reported in the literature, the present method is highly efficient when dielectrics are fully extended along the cavity length     

A multicomposite, multilayered cylindrical dielectric resonator forapplication in MMIC's

A method, based on the mode matching technique, to study various resonant modes of a multicomposite, multilayered cylindrical dielectric resonator is presented. Dielectric sphere and cone resonators placed in practical environments are investigated. The calculated resonant frequencies show very good agreement compared with the numerical results of the finite difference method for the spherical resonator and with the measured values for the conical resonator, respectively. Experimental investigations show that the conical resonator can be coupled to a circular microstrip line, which has small size at high frequencies and may be integrated together with an oscillator     

横电磁波传输室的三维FDTD法分析

本文运用时域有限差分（FDTD）法模拟电磁波在TEMcell（横电磁波传输室）中的传输，并对之进行了三维分析，给出了TEMcell中TEM模场的横截面分布及纵向分布；计算了TEM模与高阶模的谐振频率；分析了TEMcell的上限可用频率。此结果对横电波传输室的设计和使用具有重要意义。