Axisymmetric modes of cylindrical resonators with cascadedinhomogeneous dielectrics

A generic numerical scheme is developed to calculate the resonant frequency of axisymmetric modes in an inhomogeneous cylindrical dielectric resonator. The resonator consists of sections of cylindrically stratified dielectrics within a cylindrical waveguide. In each section, the TM_0m and TE_0m waveguide modes are solved by expanding the H_φ and E_φ components in terms of the eigenmodes in an empty waveguide. The fields in each section are then expanded in terms of these TM_0m and TE_0m modes. The transverse resonance technique is then applied to obtain the resonant frequencies. Comparison with literatures validates the effectiveness of this approach. Results with continuous dielectric profiles are also obtained     

High-Q LaAlO3 dielectric resonator shielded byYBCO-films

We have investigated a dielectric resonator consisting of a single crystalline LaAlO₃-cylinder shielded by a cylindrically shaped copper cavity with endplates made from epitaxial films of YBa₂Cu₃O₇ or niobium. For YBa₂ Cu₃O₇ films unloaded quality factors Q₀ of 4.5·10⁵ at 10 K and 1.3·10⁵ at 77 K were achieved at 11.6 GHz using a compact shielding cavity with a diameter of 15 mm and a height of 3.8 mm. The loss contributions of the dielectric resonator, the normal conducting cylinder wall, and the superconducting endplates, with one of them being separated by a small distance h from the dielectric cylinder, were calculated by modeling the electromagnetic fields of the TE_0νμ-modes. The dielectric loss tangent of the LaAlO ₃-cylinders was found to be 10^-6 at 4.3 K and f=11.6 GHz and to increase slightly with temperature. Moreover, the calculations indicate the tunability of the resonance frequency by changing h over a range of 1 GHz without significant degradation of Q ₀. These resonators are considered to be useful devices for stable oscillators and narrowband filters     

Resonant frequency of cylindrical dielectric resonator placed in anMIC environment

An effective dielectric constant technique to determine the resonant frequency of the TE_01δ mode of a cylindrical dielectric resonator placed in a microwave integrated circuit (MIC) environment is discussed. An expression for the dielectric constant ε_eff which makes it possible to obtain results that compare favorably with rigorous methods is given. Experimental results demonstrating the method's validity are also reported. For a given resonant frequency, closed-form expressions for computing the height of the resonator are given     

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     

Microwave measurement of temperature and current dependences ofsurface impedance for high-Tc superconductors

Perturbation formulas for TE₀₁₁-mode dielectric rod resonator and for a TE₀₁₁-mode circular cavity resonator are derived to determine the surface impedance Z_s of superconductors from measured values of resonant frequencies and unloaded Q. The relation between the maximum surface current density of a superconductor, J_s, and output power from a signal generator is derived. On the basis of these analytical results, a measurement technique is proposed to evaluate the temperature and J_s dependencies of Z_s for superconductors. The measured results of the temperature dependence of Z_s for YBCO and copper plates are presented. From these results, it is verified that the dielectric resonator is suitable for measuring the surface reactance for YBCO. From these Z_s values the temperature dependences of the skin depth and the penetration depth and those of the complex conductivity are obtained on the basis of the two-fluid model. These measured values agree well with the theoretical curves     

A low-loss bandpass filter using electrically coupled high-Q TM01δ dielectric rod resonators

For a TM_01δ mode dielectric rod resonator placed coaxially in a TM₀₁ cutoff circular waveguide, characteristics such as the resonant frequency, its temperature coefficient, the unloaded Q, and the other resonances are discussed on the bases of accurate calculations using the mode-matching method. The results show that this resonator compares favorably with a conventional TE_01δ mode dielectric resonator, particularly for realization of a high unloaded Q. Analytical results also verify that interresonator coupling between these two resonators can be expressed equivalently by a capacitively coupled LC resonant circuit. A four-stage Chebyshev filter having a ripple of 0.035 dB and an equiripple bandwidth of 27 MHz at a center frequency of 11.958 GHz was fabricated using these resonators. Its insertion loss is 0.5 dB, which corresponds to an unloaded Q of 17000, and no spurious response appears in the frequency range below 17 GHz     

一种适用于波束扫描的宽带低剖面介质谐振器天线

近年来,为解决传统介质谐振器天线（dielectric resonator antenna, DRA）体积庞大等问题,新颖的低剖面DRA如介质贴片天线和平面介质天线被提出并迅速成为研究热点.然而,现有的低剖面DRA设计要么平面尺寸较大（>0.5λ0×0.5λ0）,要么带宽较窄（<10%）,限制了它们的实际应用.文中提出了一种具有小型化平面尺寸的宽带低剖面DRA.本天线采用介质贴片设计,顶部为高介电常数的介质贴片,中间为低介电常数的介质基板,底部为缝隙馈电结构.缝隙馈电结构可激励起介质贴片谐振器的基模TE111和高次模TE131两种工作模式,这两种模式的场分布在贴片边缘部分存在基模场强较弱而高次模场强较强的显著区别.本设计巧妙地利用了该区域的模式场强区别,通过略微增加贴片边缘部分高度来显著影响高次模谐振频率而轻微影响基模谐振频率,从而将高次模TE131的谐振频率迅速下拉并与基模TE111的谐振频率靠近合并,在不增大介质贴片平面尺寸的前提条件下获得宽带工作效果.本天线的三维尺寸为0.35λ0×0.35λ0×0.08λ0 (λ0为中心频率处的空气中波长),线极化实物案例测试结果表...     

Broadband linearly polarized beat-wave TEm1/TE11 mode converters

Broadband linearly polarized waveguide mode converters have been developed to transform the high-order cylindrical TE_m1 output wave from harmonic gyrotron amplifiers into the more useful TE₁₁ fundamental waveguide mode. The converter's corrugation period is equal to the beat between the two waves and the bandwidth is predicted to be inversely proportional to the number of periods. Four-period TE ₃₁/TE₁₁ and TE₄₁/TE₁₁ converters with an azimuthal perturbation of m_c=4 and m_c =5, respectively, have yielded a peak conversion efficiency of 98% with a bandwidth greater than 3% and a one-period beat-wave converter has been designed to yield 12% bandwidth. However, it has been observed in measurements that the strong coupling in a short converter can lead to a shift of the center-frequency with an accompanying reduction of the efficiency and bandwidth. A two-period TE₄₁/TE₁₁ converter with 5% bandwidth displayed a 5% frequency shift and a conversion efficiency of only 86%     

Full-wave analysis of the image hybrid dielectric/HTS resonator

An analysis of the image hybrid dielectric/high-temperature superconductor (HTS) resonator is carried out. A full-wave radial mode-matching method is used to obtain the electromagnetic fields inside the resonator for single TE₀₁ and dual HE₁₁ modes. Measured resonant frequencies and quality factors of these modes are compared with numerical results of the analysis. The resonator power-handling capability is estimated from the field at the surface of the HTS film, assuming a certain value for the critical field of the HTS film     

用时域有限差分法研究圆柱形谐振器

本文建立了圆柱坐标系下的时域有限差分(FD-TD)算法程序。运用算法分析了几种圆柱形谐振器(包括同轴形,圆柱形介质加载和开放式柱形介质谐振器)在各种模式下的谐振频率。数值结果与理论值、实验值进行了比较,表明具有很高的精度。本文还对计算中网格的选取原则进行了探讨;并计算了一种双层介质加载腔的谐振频率,从中得出一些有益的结论。     

Numerical analysis of a TM010 cavity for dielectricmeasurement

The properties of a TM₀₁₀ cavity containing a lossy dielectric material are investigated, using the transmission-line-matrix (TLM) technique with serial nodes in cylindrical coordinates. The cavity operates at 1.1 GHz and has three concentric layers and an air gap between the sample and cavity cover. The influence of this air gap on the Q-factor and the resonant frequency is studied. Compared with the TLM method in rectangular coordinates and uniform grids, the present method is more efficient and easier to program for the analysis of the cavity with cylindrical symmetry. Computed results show that the air gap between the sample and cavity cover is very critical to the accuracy of the measurement of the dielectric property of the sample when the sample diameter is small, but negligible when the diameter is large. Unfortunately, in the case of a highly lossy sample, a small sample diameter must be used to maintain a reasonably high Q-factor. Special techniques are recommended to minimize the error caused by the air gap     

FDTD simulation of radiation characteristics of half-volume HEM and TE-mode dielectric resonator antennas

Cylindrical and rectangular dielectric resonator antennas (DRAs) using HEM_11δ, TE_11δ, and TE_01δ mode were examined to see the radiation pattern, impedance, field distribution and resonant frequency that were achieved when the DRAs were bisected through an image plane by a conducting sheet. The resultant half DRAs are smaller in volume and have a more directional radiation pattern. The elevation angle of maximum radiation was lowered in some cases. Finite-difference time-domain simulation techniques were used     

Magnetic tuning of cylindrical H01δ-modedielectric resonators

The theory of magnetic tuning of cylindrical H_01δ dielectric resonators is developed. It is based on rigorous solutions to the dielectric resonator systems containing microwave ferrites. It is shown that the most effective magnetic tuning of H_01δ dielectric resonators can be accomplished by inserting a thin ferrite rod through an axial hole in the resonator. This kind of tuning utilizes the dependence of the parallel permeability tensor component μ_z on the magnetic field applied. Experiments have been performed which show that a 4% tuning range can be attained with a Q-factor of the resonant system of the order of 2000 at X -band. Using an appropriate DC magnetic field circuit, a 120 MHz tuning bandwidth has been obtained with a consumption of tuning power of about 75 mW     

Novel TE10δ rectangular-waveguide-type resonatorsand their bandpass filter applications

New dielectric-filled rectangular-waveguide-type TE_10δ resonators are presented. A dielectric-filled rectangular waveguide section (WGS) has inductive impedance at the open-end faces. Using this property and the frequency dependency of the wave impedance of the WGS, we calculated the resonant frequency and the slope parameter of the waveguide-type resonators. The resonant frequency depends strongly on the width of the WGS and loosely on the height and the length. The calculated resonant frequencies agree well with measured data. One of the proposed bandpass filters shows highly reduced spurious up to three times the center frequency. Quality factors of the resonator and effects of a housing are also discussed     

双/三模基片集成波导和共面波导混合结构滤波器设计

针对微波带通滤波器小型化、高性能的应用需求,提出使用双/三模方形基片集成波导和共面波导混合结构设计带通滤波器.通过改变双模基片集成波导中TE₁₀₂和TE₂₀₁的谐振频率和外部耦合的强弱,可实现具有近似椭圆、非对称和无传输零点响应的双模滤波器;两个相同尺寸的共面波导作为谐振器蚀刻在基片集成波导表面,与TE₁₀₂和TE₂₀₁共同形成一个通带,设计具有多样性响应的四阶滤波器.在具有非对称响应四阶滤波器的基础上,使主模TE₁₀₁频率移动到该通带附近,设计更宽带宽的五阶滤波器.并对设计的滤波器进行加工和测试.测试结果与仿真结果吻合,表明了该混合结构设计高性能滤波器方法的可行性.     

New scattering matrix parameter formulas for transmission modedielectric resonator filter networks

New scattering matrix parameter formulas are presented for the fundamental TE_01δ mode of a cylindrical dielectric resonator, coupled with two parallel microstrip transmission lines     

Resonant modes in shielded cylindrical ferrite and single-crystaldielectric resonators

The Galerkin-Rayleigh-Ritz method is applied for computing the first few lowest resonant frequencies of cylindrical anisotropic resonators in a cylindrical cavity. The resonators are allowed to have gyromagnetic and uniaxial dielectric anisotropy with respect to the z-axis of the cylinder. Results of computations of the resonant frequencies are compared to exact solutions for many simple resonant structures and to results of experiments for more complicated structures, with good agreement. A new method of measuring permeability tensor components is presented. The method utilizes two parallel-plate cylindrical resonators operating in the HE⁺-/₁₁₁ and H₀₁₁ modes. A method of measuring the permittivity tensor components of single crystals using one parallel-plate cylindrical resonator operating in two different modes is proposed     

Diagnostics of TM010-mode microwave cavity discharges inCO2-N2-He laser gas mixtures. I. Measurement ofdielectric constant

Plasma parameters in the microwave discharged CO₂ laser gas mixtures of CO₂-N₂-He=0.9/2.5/20 at 25 Torr obtained using the perturbation method for a TM₀₁₀-mode cylindrical resonant cavity were examined. From the changes in resonant frequencies and Q values of the cavity, dielectric constant of the discharged plasma under the condition of RF to laser output power conversion ratio of 14% at mass flow rate of 4.2 kg/h was determined to be nearly 0.96-0.01j. It was also obtained from the dielectric constants of the plasma that electron number density, the electron temperature, and discharge parameters (E/n) were (0.3-3)×10¹⁵m^-3, 0.5-2.7 eV, and (0.5-2)×10^-15 Vcm², respectively     

A method of analysis of TE11-to-HE11 modeconverters

An efficient method for the determination of the scattering matrix of TE₁₁-to-HE₁₁ corrugated cylindrical waveguide mode converters has been developed, based on the representation of the fields inside the corrugations by a small number of radial waveguide modes. Numerical results show that the method, when compared to the usual mode-matching techniques, reduces the computation time without loss of accuracy     

Surface resistance measurements of HTS films by means of sapphiredielectric resonators

A sapphire dielectric resonator with a copper cylindrical shield and two endplates replaced by high-temperature superconducting (HTS) layers was used for very accurate surface resistance measurements on laser-ablated YBCO films. A system using the TE₀₁₁ mode has a resonant frequency of about 18.1 GHz and parasitic-loss Q factor of about 120000. It allows 10 mm×10 mm samples to be measured with sensitivity of ±30 μΩ. Individual samples can be measured with somewhat lower accuracy. Using larger HTS samples, one can reduce parasitic losses of the system to an unsignificant level. The exact formulas presented for the resonant system allow for avoiding calibration procedures during the evaluation of the surface resistance