Papers by Keyword: Dielectric Resonators

Abstract: Dielectric ceramics find application as dielectric resonators (DRs) in communications systems operating at microwave frequencies. RDs for this application require a unique set of properties: high value of the dielectric constant, low dielectric loss and high frequency stability. This paper presents an investigation of the correlation between the dielectric properties, the characteristics of microstructure and the crystalline phases of Ga₂O₃-doped ZnO-Nb₂O₅-TiO₂ ceramic system. The ceramics sintered at 1200 °C were characterized as for density, crystalline phases, microstructure and microwave dielectric properties. The results showed that these dielectric ceramics, obtained from the TiO₂ anatase crystalline structure, present dielectric constant and quality factor (Q) values appropriate for their use as dielectric resonators in microwave circuits. According to the experiments, as the gallium doping has raised, the dielectric constant increased, the Q factor decreased and the temperature coefficient had a tendency to decrease to a certain extent.

Abstract: The dielectric resonator (DR) is a ceramic component used in electronic circuits that can operate in microwave frequency range, where it plays the role of resonant element and enables the construction of high selective filters and oscillators. The dielectric properties of a ceramic resonator are influenced by their microstructure characteristics as pores amount. This work shows a study of the influence of pores amount (porosity) on the dielectric constant values of ceramics from ZnO-Nb₂O₅-TiO₂ system. Mixtures of Nb₂O₅, ZnO, and TiO₂ powders were compacted by uniaxial (100 MPa) and isostatic (300 MPa) pressing and sintered at 1100, 1200, and 1250°C. The experimental dielectric constant values of the sintered ceramics were corrected to eliminate the porosity influence. The results showed that the porosity, the type and quantities of crystalline chemical compounds in the ceramics influence the dielectric constant values.

Abstract: This paper presents an investigation of the correlation between dielectric properties and microstructure and TiO2 crystalline-phase characteristics (rutile and anatase) in ZnO-TiO2-Nb2O5 system ceramics. Such ceramics were produced from powder mixtures of zinc oxide, niobium oxide and titanium oxide. Powder mixtures were compressed by pressing (100 MPa uniaxial and 300 MPa isostatic) and sintered at 1100, 1200 and 1250 °C. The sintered ceramics were characterized on the crystalline phases, density and microstructure and microwave frequencies. As for the microwave dielectric properties, dielectric constant, quality factor and thermal coefficient in the temperature range from-20 to 50 °C were measured. The results showed that the type of titanium oxide structure (rutile or anatase) causes influence on the type and quantity of crystalline phases in relative density of sintered ceramics and, consequently in their dielectric properties measurements.

Abstract: This paper presents a systematic study about ceramics made of zirconium oxide and titanium oxide (ZrO2-TiO2) doped with tin oxide (SnO2), strontium oxide (SrO2) and niobium oxide (Nb2O5). These ceramics can be applied as dielectric resonators in microwave systems for telecommunications. For a good microwave performance, these ceramics must reach some parameter values as high dielectric constant and high quality factor due to the dielectric losses. The ceramics were manufactured using suitable powder mixtures of ZrO2-TiO2 with additions of 1 % of SnO2, SrO2 and Nb2O5, resulting in four different kinds of samples for analysis. The samples were compacted by an uniaxial (190 MPa) and an isostatic (300 MPa) pressing, sintered at 1200 °C for 3 hours, characterized in the chemical compound formation using X-ray Diffraction (XRD) and scanned for microstructure densification degree and grain distribution analysis in Scanning Electron Microscopy (SEM). The dielectric parameters were measured using a microwave system. The main goal of present procedure is manufacture ceramic materials for promising application as dielectric resonators.

Abstract: Automatic measurement system with multimode for microwave ceramic materials is developed. Based on traditional parallel-plate resonance method, the whole system is composed of a parallel-plate cavity, a vector network analyzer (VNA), an interface card for GPIB to USB, and a PC with measurement programs. Besides the fundamental mode, higher order resonant modes are also measured at the same time. Based on a platform of VEE, a set of analysis software is programmed with the functions of not only automatically calibrating and searching resonant frequencies but also automatically computing and displaying the dielectric parameters of microwave materials with high reliability and efficiency in a wide frequency range.

Abstract: In this paper, several kinds of synthesis techniques were adopted; not only conventional solidstate reaction method but also solution synthesis techniques, including co-precipitation and hydrothermal synthesis, in addition to the gel-casting for complex shape of ceramic components and tape-casting of large scale thin plate for microwave IC. Different kinds of microwave ceramics were prepared, such as materials with low permittivity and high quality factor, moderate permittivity and good quality factor, and, high permittivity and reasonable quality factor, in addition to near zero of temperature coefficient of resonance frequency. Series of microwave devices were developed, for examples, dielectric resonators, dielectric filters, GPS antennas, communication connectors, and thin substrates for microwave IC.

Abstract: Tin titanate zirconate (ZTS) is widely known for its good dielectric properties at high frequencies and has been widely employed as a dielectric resonator. ZTS does not sinter easily by solid state difusion and it is necessary to introduce sintering aids capable of increasing diffusion coefficients and/or leading to liquid phase sintering. Consequently, the dielectric properties in microwave frequencies can be reduced. This work focused on the utilization of high energy ball-milling as a method of reducing initial particle size and further improving sintering of ZTS.The powders obtained were characterized by X-ray diffraction as a function of milling time, as well as by a light scattering particle size analyzer.

Abstract: The effects of different concentrations of ZrO2 on the microstructure and dielectric properties of barium nanotitanate (Ba2Ti9O20) dielectric resonators (DRs) for microwave applications are reported. High dielectric constant, small dielectric loss as well as frequency high stability are very important for use in microwave telecommunication, particularly, in a local oscillator of an INPE Communication Satellite. Three different samples of Ba2Ti9O20 with different percentages of ZrO2 were prepared: with 2.0, 2.46 and 3.0 mol% dopant content. The dielectric constant and unloaded quality factor were determined for each different sample.