The microwave characteristics of two dielectric resonator materials were investigated. This research included (Zr, Sn)TiO4, a material having the characteristics of a dielectric constant K= 38, Q= 7000 at 7 GHz, and temperature coefficient of resonant frequency τf, = 0 ppm/°C. The investigation determined the relations between the dielectric loss and micro-structures of this ceramic. Analysis by X-ray microanalyzer made it clear that the addition of Fe2O3 increased the dielectric loss of this ceramic because the Fe ions diffused into the grain. The other material investigated was BaO-PbO-Nd2O3-TiO2, a ceramic having a dielectric constant of K= 88, Q= 5000 at 1 GHz, and τf= 0 ppm/°C. As this ceramic has a very high dielectric constant, it is useful for applications at frequencies <1 GHz.

Microwave Characteristics of (Zr, Sn)TiO4 and BaO‐PbO‐Nd2O3‐TiO2 Dielectric Resonators

Since 1970s, many kinds of dielectric resonator materials with improved Q values and improved temperature coefficients have been developed. Representative of them are the systems, (Ba, Sr, Ca)(Zr, Ti)O3, MgTiO3-CaTiO3-La2O3 · TiO2, Ba2Ti9O20, (Zr, Sn)TiO4, (Sr, Ca)[(Li, Nb),Ti]O3, and BaO-Nd2O3-TiO2. In the past 15 years, the Q values of these materials have gradually been improved. Using these new materials, dielectric resonator filters and oscillators are being developed which are more compact and applicable to high power operation. Their main applications are cellular mobile radio systems and SHF-TV systems using direct broadcasting satellite. This paper will present the recent development in Japan of resonator materials and filters.

Recent development of dielectric resonator materials and filters in Japan

Ceramics with compositions in the solid solution region of the ZrO2-TiO2-SnO2 equilibrium diagram are finding wide application as dielectrics in filters for communications and radar systems operating at microwave frequencies. Commercially available compositions often incorporate sintering aids and dopants to reduce processing temperatures and modify the dielectric properties. However, the mechanism through which these additives influence dielectric loss is not obvious. The role of zinc oxide as a sintering aid and lanthanum and niobium as dopants, their effect upon microstructural development and their correlation with dielectric loss at microwave frequencies were investigated. For specimens of density greater than 90% theoretical, the influences of defect chemistry upon dielectric loss appear to dominate those of the microstructure. Properties close to those which might be considered intrinsic were attained through sintering for periods of up to 128h. Doping with lanthanum is detrimental to the dielectric loss, particularly after long sintering times.

Relationships between dopants, microstructure and the microwave dielectric properties of ZrO2-TiO2-SnO2 ceramics

Dielectric resonators are being used in microwave filters and oscillators now that high-dielectric-constant, high-Q, temperature-stable ceramics have been developed. This paper reviews dielectric resonators with emphasis on applications, contains tutorial material, deseribes new 2-, 4-, and 6GHz bandpass filters, and presents several examples of oscillator applications. A complete blbliography to English language publications on dielectric resonators is included.

Application of Dielectric Resonators in Microwave Components

Microwave measurements of Ba2Ti9O20 show that this ceramic is uniquely suited for dielectric resonators. (Suitable ceramics should have a high dielectric constant K, a low dielectric loss (high Q), and a low temperature coefficient of resonant frequency, τ.) At 4 GHz, Ba2Ti9O20 resonators have Q >8000, K= 39.8, and τ=2 ppm/°C. Measurements of Q and τ were made on unmetallized ceramic resonator disks positioned in a waveguide; K was measured using a dielectric post resonator technique. From 4 to 10 GHz, Q approaches that for a copper waveguide cavity, whereas the temperature coefficient is typically 8 times lower.

Ba2Ti9O20 as a Microwave Dielectric Resonator

The compounds SrZrO3 and CaZrO3 combine high permittivity with low loss and positive temperature coefficient of permittivity. Temperature-stable materials were produced by forming solid solutions between these zirconates and zirconates or titanates having negative coefficients. The properties of temperature-stable compositions in the systems Ca(Zr,Ti)O3 and (Ba,Sr)(Zr,Ti)O3 were investigated. At 4 GHz the relative permittivities were from 29 to 35 and the loss tangents from 3 to 11×10−4. Both permittivity and microwave loss increased as the principal alkaline-earth ion was changed from Ca to Sr to Ba, but the higher losses could be reduced by adding ∼1 mol% Nb or Ta. Dense fine-grained ceramics with the properties required for microwave applications were prepared.

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High-Permittivity Temperature-Stable Ceramic Dielectrics with Low Microwave Loss

Die Verbindungen SrZrO3 und CaZrO3 besitzen eine hohe Dielektrizitatskonstante mit geringem Verlust und einen positiven Temperaturkoeffizienten der Dielektrizitatskonstanten.

R. C. Kell

Papers

High-Permittivity Temperature-Stable Ceramic Dielectrics with Low Microwave Loss

High‐permittivity temperature‐stable ceramic dielectrics with low microwave loss

Low-Loss Temperature-Stable High-Permittivity Microwave Ceramics