Improvement of accuracy in measurements of the surface resistanceof superconductors using dielectric resonators

Two techniques to minimize the influence of parasitic losses on surface resistance measurements of superconductors employing dielectric resonators have been described. The first method optimizes the sapphire resonator aspect ratio to minimize the parasitic losses for given superconductor sample dimensions and measurement frequency. The second utilizes a reference resonator with a perfect conductor plane to cancel out the influence of parasitic losses by measurements of the resonant frequencies and Q-factors of two resonators. The second technique is recommended when materials having noticeable dielectric losses are used to construct dielectric resonators     

Accurate measurement of Q-factors of isolated dielectric resonators

In this paper, a set-up used to accurately measure the resonant frequencies and Q-factors of isolated dielectric resonators is described. The measured resonant frequencies and Q-factors of first five lowest order modes of two cylindrical dielectric resonators of relative permittivity 38.0 and 79.7 respectively are reported. The measured values are compared with those of rigorous numerical methods available in the literature     

Study of whispering gallery modes in anisotropic single-crystaldielectric resonators

The Rayleigh-Ritz method and the finite element method nongenerating spurious solutions are employed for analysis of whispering gallery modes (WGMs) in cylindrical single-crystal anisotropic dielectric resonators. These methods allow accurate computation of the resonant frequencies, the Q-factors (depending on the dielectric and on the conductor losses), and the electromagnetic field distributions for all WGMs in the presence of additional elements like metal shields, MIC substrate, or supports. Different families of modes are studied both theoretically and experimentally. The mode coupling phenomenon is investigated. A WGM single-crystal quartz resonator is presented having an unloaded Q-factor greater than 30000 at about 100 GHz, including radiation and dielectric losses     

Influence of substrate conductivity on characteristics of ZnO/SiO2-diaphragm piezoelectric resonators

Most of the ZnO/SiO2-diaphragm piezoelectric composite resonators on silicon substrates exhibit Q-factors of the anti-resonance much lower than those of the resonance. It is demonstrated both theoretically and experimentally that this is caused by the conductivity of the substrate.     

Dual-mode filters with conductor-loaded dielectric resonators

In this paper, a new class of dual-mode microwave filters is presented. These devices use conductor-loaded dielectric resonators with unloaded Q-factors of 2000-8000 achievable in half the physical size of TEM filters and with good spurious performance. The basic properties of this resonator have been examined with the aid of a finite-element field-analysis package. Fundamental design rules for bandpass filters have been developed. A design example of a transmit filter for a ground-signal-metal cellular-radio base station is demonstrated     

High-Temperature Measurements of Q-Factor in Rotated X-Cut Quartz Resonators

The Q-factors of piezoelectric resonators fabricated from natural and synthetic quartz with a 34° rotated X-cut orientation have been measured at temperatures up to 325°C. The synthetic material, which was purified by electrolysis, retains a high enough Q to be suitable for high-temperature pressure-transducer applications, whereas the natural quartz is excessively lossy above ~200°C application. The present results are compared to results obtained previously at AT-cut resonators.     

Radiation Loss from Open-Circuited Dielectric Resonators (Short Papers)

The Q factor of an open-circuited resonator is influenced by dielectric, conductor, and radiation losses. This short paper discusses these losses and shows that insight into the radiation loss can be obtained by an extension to the analysis given by Lewirt. This shows that the radiation loss is a maximum for the dominant mode and that provided the permittivity is not less than 9.0 the radiation losses are at a minimum for the second mode. It is suggested that these results may be applied to the design of filters based on dielectric resonators. The application of the results to stripline resonators in which the dielectric extends past the termination of the upper conducting strip is more difficult, and it is suggested that experimental work is required to investigate postulated improvements. Finally, some of the radiation patterns of the open-circuited dielectric resonators, obtained in this paper, show interesting directional properties which may be applied to the design of antenna systems.     

Accurate characterisation of DR coupling with new general-purpose CAD program

It is demonstrated that microwave structures incorporating dielectric resonators (DR) are accurately characterised by means of a 3-dimensional finite-difference CAD package. All major assumptions made so far have been dropped, offering the possibility of a rigorous analysis of the embedding of dielectric resonators into microwave structures. In particular, a finite thickness for the microstrip conductor has been taken into account. The coupling of the DR to a microstrip placed in a metallic housing has been theoretically and experimentally investigated. Theoretical and experimental results are in good agreement and give new insight into DR coupling to microstrip circuits.<>     

Analysis of mode characteristics for deformed square resonators by FDTD technique

The mode frequencies and quality factors (Q-factors) in two-dimensional (2-D) deformed square resonators are analyzed by finite-difference time-domain (FDTD) technique. The results show that the deformed square cavities with circular and cut corners have larger Q-factors than the perfect ones at certain conditions. For a square cavity with side length of 2 /spl mu/m and refractive index of 3.2, the mode Q-factor can increase 13 times as the perfect corners are replaced by a quarter of circle with radius of 0.3 /spl mu/m. Furthermore the blue shift with the increasing deformations is found as a result of the reduction in effective resonator area. In square cavities with periodic roughness at sidewalls which maintains the symmetry of the square, the Q-factors of the whispering gallery (WG)-like modes are still one order of magnitude larger that those of non-WG-like modes. However, the Q-factors of these two types of modes are of the same order in the square cavity with random roughness. We also find that the rectangular and rhombic deformation largely reduce the Q -factors with the increasing offset and cause the splitting of the doubly degenerate modes due to the breaking of certain symmetry properties.     

Rapid calculation of the Green's function in a rectangular enclosure with application to conductor loaded cavity resonators

A new technique for rapid calculation of the Green's functions in a rectangular cavity is presented. The method is based on a best polynomial approximation in three dimensions, which is implemented through a fast cosine transform. Generating the required samples for polynomial modeling is greatly accelerated through Ewald summation technique. To validate the efficiency of the resulting Chebyshev series for the potential Green's functions, a surface integral-equation (SIE) formulation is used to compute the resonant frequency of conductor loaded cavity resonators. The new scheme is proved to be considerably faster than Ewald transform in filling the method of moments (MoM) matrix. A SIE with the MoM can now be efficiently used for electromagnetic analysis and optimization of conductor or dielectric loaded resonators and filters with rectangular enclosures.     

Attenuation of a shielded rectangular dielectric rod waveguide

The attenuation coefficient of a rectangular dielectric line enclosed by a rectangular shield is obtained by the use of a rigorous mode-matching method to calculate the required mode field intensity. The cross section of the waveguide is overlaid by a grid, and numerical integration is used to determine the power flow, dielectric, and conductor losses and respective attenuation coefficients. To obtain experimental verification, a length of waveguide was made into a resonator, and measured and calculated Q factors were compared. The results for the E/sup y//sub 11/ mode show how the influence of the shield decreases with distance. This is relevant to the design of dielectric waveguide structures and in filter applications where dielectric resonators are used.     

Coupling and quality factors in parallelepiped nonradiative dielectric resonators

In this work, the quality factors and the coupling effects have been investigated for parallelepiped dielectric resonators in nonradiative dielectric (NRD) waveguide, in order to achieve fundamental information for the design of various types of advanced filters. The unloaded quality factor has been calculated taking into account both conductor and dielectric losses through a straightforward version of the perturbation method. The electromagnetic coupling as a function of the distance between NRD guide and resonators has been evaluated through proper extensions of typical lumped equivalent circuits, thus quantifying resonance frequency shifts, external and loaded quality factors, etc.. To validate the derived theoretical models, suitable measurements of all these parameters have been performed at microwaves on X-band NRD prototypes.     

一种基于介质谐振器的新型电磁超材料

文章设计了一种基于介质谐振器的新型混合左右手结构。该结构由工作在横电模式TE的介质谐振器嵌入到平行平板波导中组成。数值分析表明：工作频带为12 GHz～14 GHz,在13.15 GHz频率下相移为零。该结构在整个通带内插入损耗低于0.6 dB,同时具有极低的通带波纹,表现出了良好的传输特性。与普通的混合左右手结构相比,其结构简单,插入损耗较低,在高频时导体损耗也较低,在超级透镜、天线等领域具有很好的应用前景。     

Suppression of bulk-scattering loss at s.a.w.-resonator reflectors

Tapering of the groove depth at the edges of grooved-array reflectors is shown to be effective in suppressing surface-to-bulk-wave conversion losses at such reflectors in an s.a.w. resonator. With such tapering, Q-factors of 80,000 at 174 MHz and 61,000 at 157 MHz have been measured on evacuated LiNbO3 and s.t.-quartz resonators, respectively. These measurements were made on `empty? resonators having no transducers between the gratings. The latter value is within 3% of the best estimate of the material Q-factor of 63,000 at 157 MHz.     

Computations of Frequencies and Intrinsic Q Factors of TE/sub 0nm/ Modes of Dielectric Resonators (Short Papers)

The Rayleigh-Ritz method is described, which is used to calculate the resonant frequencies and intrinsic Q factors due to dielectric losses of quasi TE/sub onm/ modes of dielectric resonators. Electromagnetic fields of an auxiliary post dielectric resonator are taken as an electrodynamics basis for approximate solutions of this problem. The method provides upper bounds for true resonant frequencies. Numerical results are compared with previously published complementary calculations. The influence of a dielectic substrate on resonant frequencies and intrinsic Q values is demonstrated.     

Provisional model technique in the FDTD analysis of high-Q resonators

We propose A technique for extracting Q-factors and resonant frequencies of resonators from signal models constructed using samples provided by a time-domain simulator. The method involves two models. The first model is a provisional one and serves one to generate additional samples that prevent the original sequence from being corrupted during signal processing. The second model is the final one and gives directly the quality factors and the resonant frequencies for the structures of interest. We show the application of the new technique to the fast time domain analysis of structures with the unloaded Q-factor exceeding 106.     

Comparison of Q-Factors Between TE and TM Modes in 3-D Microsquares by FDTD Simulation

Mode characteristics of three-dimensional (3-D) microsquare resonators are investigated by finite-difference time-domain (FDTD) simulation for the transverse electric (TE)-like and the transverse magnetic (TM)-like modes. For a pillar microsquare with a side length of 2 mum in air, we have Q-factors about 5 times 10³ for TM-like modes at the wavelength of 1550 nm, which are one order larger than those of TE-like modes, as vertical refractive index distribution is 3.17/3.4/3.17 and the corresponding center layer thickness is 0.2 mum. The mode field patterns show that TM-like modes have much weaker vertical radiation coupling loss than TE-like modes. TM-like modes can have high Q-factors in a microsquare with weak vertical field confinement.     

Silicon-based high-Q inductors incorporating electroplated copperand low-K BCB dielectric

We have fabricated high-Q copper inductors using low-K benzocyclobutene (BCB) dielectric as an interface layer on standard CMOS silicon substrate. Metal ohmic loss and substrate loss, the two major factors that degrade the Q-factors of on-chip inductors, are suppressed by the employment of electroplated copper and the BCB dielectric, respectively. The inductors exhibit Q-factors as high as 25 at 2 GHz. The dependence of inductor's high-frequency performance on inductor's parameters, such as BCB and copper thickness, has been investigated in detail. The inductor fabrication process is low-cost and low-temperature, making it suitable for post-IC process for high-performance RFICs and MMICs     

Increasing Q-Factor of Planar Dielectric Resonators with Whisper Gallery Modes

Planar dielectric resonators (DR) with height significantly lower than the operating wavelength are investigated as a new class of disk dielectric resonators of the millimeter wavelength range with whispering gallery (WG) modes. It is known that in the open state, such resonators based on the WGmodes are not excited due to high radiation losses. It is shown that the solution of this problem is the partial shielding of the disk dielectric structures with a plane-parallel screen by placing the disk between two flat conducting mirrors. It has been established that by introducing an air gap between the flat base of the dielectric disk and one of the conductive mirrors, it is possible to increase the quality factor of the planar DR almost twice. One of the reasons for this is the partial displacement of the resonant field of the WG modes from the dielectric region to the air gap, where the dielectric losses are lower. In addition, an increase in the air gap in the range of optimal values, comparable to half the working wavelength, leads to a decrease in ohmic losses. The above causes an increase in the quality factor of planar DR as an air gap is extended.     

FM noise measurement of w-band impatt diodes with a quasi-optical direct detection system

A simple and accurate method for determining the FM noise of negative-resistance regenerative oscillators in the microwave region is the so-called direct detection system, where the FM-AM noise conversion is achieved with a discriminator, usually a high Q-factor cavity. With increasing oscillator frequency (above 30 GHz), however, it becomes increasingly difficult to obtain reliable discriminators with high Q-factors. This difficulty can be overcome by applying high-quality quasi-optical resonators for the FM-AM noise conversion.