Quasi-optical Dielectric Resonator Research Articles

Особенности межтипового взаимодействия в дисковых квази-оптических диэлектрических резонаторах при внутреннем возбуждении паразитных типов колебаний

Особенности межтипового взаимодействия в дисковых квази-оптических диэлектрических резонаторах при внутреннем возбуждении паразитных типов колебаний

Influence of the Refractivity and Temperature of the Ambient Medium on the Eigenfrequencies of Quasioptical Cylindrical Dielectric Resonators

UDC 537.86 We attempt for the first time to separate the influences of the temperature and refractivity of the ambient air space on the spectral and energy characteristics of cylindrical Teflon and leucosapphire resonators with the whispering gallery modes in the millimeter-wave range. It is found that under conditions of natural fluctuations of the above-mentioned factors of the studied ambient medium, the degree of temperature influence on the resonator eigenfrequencies is more significant. We demonstrate that quasioptical cylindrical dielectric resonators can be used as sensors of the temperature of the ambient air medium and ensure an accuracy of 10 −4 ◦ C when their resonant frequencies are measured with an accuracy of 100 Hz. A method for determination of the air refractivity has been developed, which uses the considered resonator as a temperature sensor and a measuring cell of the microwave resonator refractometer. A refractometer sensor has been developed on the basis of two identical resonators with whispering gallery modes. The differential two-resonator refractometer compensates for the influence of changes in the temperature of the ambient medium on the measured difference of the eigenfrequencies of resonators with identical modes. It is found that the accuracy of determination of the air refractivity is ensured at a level of 10 −2 if the frequency difference is measured with an accuracy of 10 Hz.

A Unique Ka-Band Measurement System Based on Quasi-Optical Dielectric Resonator Technology for Studying Small Superconducting Samples

A new measurement system for microwave property study has been developed. Modified from the standard quasi-optical dielectric resonator technique, the sapphire cylinder resonator excited with whispering gallery modes has a narrow slit along the radius, within which a piece of small-sized single crystal or thin film sample can be positioned. Sandwiched by two pieces of YBCO films, the resonator is sealed in a specially designed vacuum vessel, which is soaked in liquid <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> He. A microwave signal is coupled to the vacuum vessel by stainless steel thin wall waveguides and then to the resonator by sapphire waveguides. Coupling between the resonator and the two sapphire waveguides can be controlled accurately during the measurement. Furthermore, a decompressed liquid <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> He port has been designed in the vacuum vessel so as to extend the measurement to lower temperatures down to 2.6 K. A high-quality single crystal pnictide superconductor of BaFeNiAs was used for testing.

Auto-oscillatory system based on dielectric resonator with whispering-gallery modes

The generation mechanism of microwave radiation in the system with azimuthally-periodical current of an electron beam that excites a high-Q quasi-optical dielectric resonator was developed. Eigen parameters of a cylindrical Teflon resonator were determined. Radiation was locked in the investigated system by a detector of 8-mm wave band. Design philosophy of microwave oscillators with high-Q resonators, in which electromagnetic “whispering gallery” modes are excited by electron beam, was developed.

Millimeter-Wave Surface Impedance Characterization of HTS Films and Single Crystals Using Quasi-Optical Sapphire Resonators

High-Q sapphire quasi-optical dielectric resonators (QDRs) excited on whispering-gallery modes are key techniques for accurate characterization in millimeter (mm) wavelength range of surface impedance of HTS large-area films and can be useful for impedance characterization of small HTS single crystals, including various unconventional superconductors. Hemispherical QDR-based technique for mm impedance characterization of HTS films is analysed theoretically and confirmed experimentally. Such an approach can be applied to QDR of modified forms. The temperature dependences of the YBaCuO films resistance properties using hemispherical resonator and the iron-pnictide single-crystal impedance properties using radially-slotted one are measured in Ka-band.

QUASI-OPTICAL ANNULAR SAPPHIRE RESONATOR WITH INTERNAL CYLINDRICAL CONDUCTOR

A new approach to measurement of the surface resistance Rs of large conductive samples is investigated. The technique for determining Rs with the use of an open annular quasi-optical dielectric resonator in which whispering gallery modes are excited, is presented. The basic characteristics of the cavity resonator have been investigated both theoretically and experimentally within the frequency range from 30 to 40 GHz. The possibility to apply an annular dielectric resonator for measurement Rs of high-temperature superconductors is demonstrated.

Quasioptical Sapphire Resonators in the Form of a Truncated Cone

This paper reports on a detailed experimental study of quasioptical dielectric resonators (QDRs) designed in the form of a truncated cone and excited on whispering-gallery modes. One aim of this paper is to study of the eigenfrequency spectrum and quality factors of single-crystal sapphire resonators. A second aim is to show the applicability of the resonator technique not only in optical but also in the millimeter-wave range, in particular, for studying the surface resistance (Rs) of high-temperature superconducting films. The measured frequencies of QDR as a function of the wedge angle of the cone resonator are in a good agreement with those frequencies simulated using the CST Microwave Studio 2006 program. Additionally, electrodynamic characteristics of the cone resonator and hemispherical dielectric resonator with conducting endplate are compared.

Improvement of Coupling Characteristics of Sapphire Quasioptical Dielectric Resonator by Microstrip Line

Improvement of Coupling Characteristics of Sapphire Quasioptical Dielectric Resonator by Microstrip Line

Two-layered disc quasi-optical dielectric resonators: electrodynamics and application perspectives for complex permittivity measurements of lossy liquids

Electromagnetic properties of novel quasi-optical resonators are studied theoretically and experimentally. The resonators are a radially two-layered dielectric disc sandwiched between conducting endplates. The internal layer can be filled with air or lossy liquid. Whispering gallery modes are excited in such a resonator and the mode energy is concentrated near the inner side of the cylindrical surface of an external layer. The measurement data obtained in the Ka-band are compared with theoretical calculations of eigenfrequencies and quality factors of the Teflon resonator filled with water, ethyl alcohol, benzene and aqueous solutions of ethyl alcohol. A number of ‘anomalous’ properties of the resonator can be described using Maxwell equations. The experimental data on the complex permittivity of a binary mixture water–ethyl alcohol are compared with the values calculated in terms of Debye's function. An important feature of the proposed technique is that it holds promise for making first principle microwave measurements of the permittivity of lossy liquids.

Active Oscillator Stabilized by Axial-Laminated Quasi-Optical Dielectric Resonator Such as Dielectrometer Cell

Active Oscillator Stabilized by Axial-Laminated Quasi-Optical Dielectric Resonator Such as Dielectrometer Cell

QUASI-OPTICAL DIELECTRIC RESONATORS WITH SMALL CUVETTE AND CAPILLARY FILLED WITH ETHANOL-WATER MIXTURES

Electrodynamic properties of quasi-optical dielectric resonators (QDRs) of two types with liquid-filled small cavities have been studied. Both eigen frequency and energy loss in the resonators depending on dimensions of the cavities are presented. One of the QDR types is a two-hemidisc resonator with a diametrical slot in which a cuvette with a thin (0.01– 0.1 mm) flat liquid layer is placed and the other is a disc resonator with a small diameter (0.3–2 mm) cylindrical capillary. Measurements have been carried out at room temperature in Ka-waveband by using the resonators made of Teflon material. The obtained results allow to conclude that the given approaches to the development of measuring technique for characterization of liquids in small and with arbitrary loss tangent (for example, water and aqueous solutions) are quite perspective. Advantages and disadvantages of each resonator are considered briefly. The necessity to carry out both theoretical description of the electrodynamic properties of the QDR containing small liquid-filled cavities and determination of maximal sensitivity conditions for the measurement techniques is underlined.

Microwave properties of HTS films: measurements in the millimeter wave range

A theoretical and experimental justification of an approach proposed and developed by us for surface impedance standard measurements of HTS films is presented. An analysis of the electromagnetic properties of quasi-optical dielectric resonators with conducting endplates, which provides a theoretical background for studies of HTS films in the millimeter wave range, is performed. With this technique, the highest-quality modes, namely whispering gallery modes, are excited in a dielectric cylindrical disc sandwiched between HTS films. Considerable enhancement of the sensitivity of surface resistance measurements in the millimeter wave range is demonstrated, which is important for the fundamental investigation of superconductor physics. It is also shown that the measured frequency shift in the resonator with the HTS endplates as a function of the temperature reveals a possibility for accurate evaluation of the field penetration depth in HTS films.

Effect of a ring layer filled with various substances on the eigenfrequency and Q-factor of a cylindrical quasi-optical dielectric resonator

The influence of a ring layer filled with various substances on the eigenfrequency and Q-factor of a cylindrical quasi-optical dielectric (Teflon) resonator has been investigated. The spectral and energy characteristics of an axially homogeneous whispering gallery eigenmode of this resonator are analyzed for the first time as dependent on the radius and thickness of the ring layer. It is established that the eigenfrequency behaves differently when the ring layer is filled with liquids characterized by large and small losses.

&amp;lt;tex&amp;gt;$Q$&amp;lt;/tex&amp;gt;-Factor Measurement of Quasi-Optical Dielectric Resonators Under Conditions of the Whispering Gallery Mode Degeneration Removal

An approach that allows one to determine the unloaded quality factor of a quasi-optical dielectric resonator (QDR) under conditions of the resonance line splitting corresponding to twofold degenerative whispering gallery (WG) mode has been proposed. The resonator is represented by an equivalent network as two oscillatory circuits with a certain coupling between them. The approach allows one to determine the Q-factor of a single oscillatory circuit using three measured parameters, namely: 1) ratio between specific amplitudes of the resonator amplitude-frequency response (or its second derivative); 2) resonant frequency; and 3) frequency splitting of the response (or its respective second derivative). The proposed technique is illustrated by the measurements in the millimeter-wave range for sapphire quasi-optical resonators with conducting and high-T/sub c/ superconducting (HTS) film endplates.

Microwave Losses in a Quasioptical Dielectric Resonator as a Function of the Thickness of Ultra-Thin Conducting Endplates

Microwave Losses in a Quasioptical Dielectric Resonator as a Function of the Thickness of Ultra-Thin Conducting Endplates

Measurements of Millimeter-Wave Surface Resistance and Temperature Dependence of Reactance of Thin HTS Films Using Quasi-Optical Dielectric Resonator

The technique proposed by authors earlier for accurate measurement of large-area HTS thin film surface resistance (R/sub s/) is developed further. It is based on application of quasioptical dielectric resonators (QDR). Data on R/sub s/ of individual Y-123 films obtained at 77 K by using "round robin" procedure are presented. The main attention is paid to developing technique of temperature dependence measurement of thin film surface reactance variation (/spl Delta/X/sub s/). The dependence obtained by experiment is analyzed by means of fitting procedure that allows one to determine the validity of theoretical models for the temperature dependence of field penetration depth. Particularly, the 3D XY critical regime, Ginzburg-Landau behavior and two-fluid model are compared near T/sub c/. Our data show that the former approach best follows the observed dependence.

Conical Quasioptical Dielectric Resonator

A dielectric resonator of the new type—conical quasioptical dielectric resonator—is proposed. The dependence of the resonance oscillation frequency, the quality factor, and the electric field distribution on the cone angle of such a resonator with a conducting screen in the base plane has been experimentally studied in the 8-mm (Ka-band) wavelength range.

Investigation of Dielectric Characteristics of Binary Solutions by Means of Self-Excited Gunn-Effect Oscillator Stabilized by Partly Shielded Quasi-Optical Dielectric Resonator

Investigation of Dielectric Characteristics of Binary Solutions by Means of Self-Excited Gunn-Effect Oscillator Stabilized by Partly Shielded Quasi-Optical Dielectric Resonator

Microwave impedance characterization of large-area HTS films: a novel approach

We recently reported a method for measuring the microwave surface resistance(Rs) of large-area HTS films. The device was formed from a sapphire quasi-opticaldielectric resonator (QDR) with conducting end-plates (CEP). In the present work,Rs-measurement procedures and data obtained under different conditionsare systematically analysed. The accuracy and the sensitivity of theRs-measurement are analysed. The results of the study clearly demonstrate that the proposedtechnique provides a sensitivity which is increased by at least one order in comparison withthe most accurate cavity resonator techniques in the millimetre wave range. In addition,the first experimental results on the temperature dependence of the QDR resonances withdifferent CEP (HTS and/or Cu) are discussed in terms of a surface reactance(Xs) measurement.

On the negative value of dielectric permittivity of the water surface layer

The present letter reports on experimental measurements of a resonant frequency shift of a radially two-layer quasioptical dielectric resonator with whispering gallery wave modes when the internal layer is water or benzine. The sign of the shift indicates that the real part of dielectric permittivity of the water surface layer adjacent to a solid-state dielectric becomes negative (ε′&amp;lt;0). The measurements were carried out at room temperature in microwave K band.