Study On Mid-permittivity Microwave Dielectric Ceramics And Its Application On Cavity Filter

With the development of mobile and satellite communications technology in recent years, the market demands more and more high-performance and miniaturized microwave devices. Microwave dielectric ceramics have been given abroad attention as essential materials of microwave devices. Because of the rapid development and upgarading of mobile communications, markets demand more and more communication base stations with high performance. This gives microwave dielectric ceramics with medium dielectric constant which is used in communication base stations not only new opportunities, but also higher performance requirements.In this paper, CaTiO3-NdAlO3 ceramic system with medium dielectric constant had been studied and developed. We studied the ratio of the components of CaTiO3 and NdAlO3 and modification of CaTiO3-NdAlO3 ceramic by adding low melting B2O3 as a sintering aid. After testing and analyzing the CaTiO3-NdAlO3 ceramic’s density, phase composition, microstructure morphology and microwave dielectric properties, we found that the temperature coefficient of resonance frequency of xCaTiO3-(1-x)NdAlO3ceramic tended to zero when x was 0.7. CaTiO3-Nd AlO3 ceramic doped with 0.2wt%B2O3 sintered at 1425℃ could get the best microwave performance : εr = 46.2, Q×f =30927GHz, τf = 6.1ppm/ ℃. Cosolvent not only reduced the sintering temperature of CaTiO3-NdAlO3 ceramic, but also gave the ceramic good quality factors and temperature stabilities.A new kind ceramic system with medium dielectric constant BaLa4Ti4O15 has been studied. We improved the preparation technology of Ba La4Ti4O15 ceramic and did the research about the modified BaLa4Ti4O15 ceramic under the influence of different sintering aids(CuO, BCB, H3BO3) with low melting points. After testing and analyzing the BaLa4Ti4O15 ceramic’s density, phase composition, microstructure morphology and microwave dielectric properties, we found that BaLa4Ti4O15 ceramic calcined at 1200℃and sintered at 1525℃got excellent microwave properties : Q×f = 34991 GHz, εr = 45.6.BaLa4Ti4O15 ceramic doped with 0.1wt% sintering aids H3BO3 was sintered at 1375℃,the samples performed excellent dielectric properties : Q×f = 31705 GHz, εr = 43.2.After BaLa4Ti4O15 ceramic was modified by H3BO3, its sintering temperature reduces150 ℃. Meanwhile, microwave performance was still excellent. This greatly reduced BaLa4Ti4O15 ceramic’s cost of production, and improved its competitiveness in the mobile communication.We designed and produced a dielectric filter based on ceramic material of BaLa4Ti4O15 ceramic with good microwave properties. Through that, we could validate the performance of new microwave dielectric ceramic materials. The filter got excellent performance: center frequency f0 = 2.6GHz, passband insertion loss ≤1dB, the band return loss ≥18dB, stopband rejection ≥25dB which satisfied our project indicators.Experiment showed that the new type of microwave dielectric ceramics could be well applied to dielectric cavity filter and the filter had a excellent performance.