Study of Microwave Dielectric Resonators and Filters

• Main Authors: Yao-Chung Chen, 陳耀忠
• Other Authors: Cheng-Liang Huang
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/90546041596629349760

博士 === 國立成功大學 === 電機工程學系碩博士班 === 90 === Due to the development in mobile communication, mobile telephone systems, as well as in satellite broadcasting systems was rapidly, how to design the high-quality devices applied in analog circuit is the most important homework. There are two primary branches in this research. One part is to develop the dielectric ceramic systems that exhibit great dielectric properties. The other part is to design and realize the coaxial-type dielectric filters. 1.Study and fabrications of microwave dielectric resonators (a) The effect of CuO, ZnO and V2O5 additions to ReAlO3 (Re=Sm and Nd) were investigated. The sintering temperatures of ReAlO3 ceramics can be effectively reduced from 1650℃ to 1410~1430℃ due to the liquid-phase sintering effect. At low concentration levels (0.25-0.5 wt％), the ReAlO3 ceramics remained in the single phase and presented second phase Sm4Al2O9 and Nd4Al2O9 on SmAlO3 and NdAlO3, respectively with concentrations over 0.5 wt%. The Q×f values of 51000 and 41000 GHz was obtained at 1430℃ for 0.25 wt% CuO and ZnO-sintered SmAlO3 ceramics. The Q×f value of 63000 GHz was achieved at 1410~1430℃for 0.25 wt% CuO-sintered NdAlO3. The relative dielectric constant of ReAlO3 remains in the range from 19.6 to 22.5. The temperature coefficient of ReAlO3 ceramics depends on the additions and ranges from –30 to -65 ppm/℃. (b) The microwave dielectric properties and microstructure of Ba2-xSm4+2x/3Ti8+yO24+2y were investigated. The typical dielectric performances of εr = 68 to 79 and Q×f = 11000 to 12500GHz were obtained in well-sintered Ba2-xSm4+2x/3Ti9O26 ceramics. The τf values of Ba2-xSm4+2x/3Ti9O26 ceramics was adjusted from negative (－3ppm/℃ for x = 0) to positive ( + 6ppm/℃ for x = 0.3). The Ba2-xSm4+2x/3Ti8+yO24+2y ceramics with x = 0.1~0.3 and y = 0~2 formed the complete solid solution and were obtained in this reach. The typical dielectric performances of εr = 63 to 85 and Q×f = 8500 to 13000GHz were obtained. The τf values of the BST ceramics can be adjusted from a negative –12 ppm/℃ value to a positive value 17 ppm/℃ as y increases from 0 to 2. Second phases Ba2Ti9O2 and TiO2 appeared during sintering procedures and were identified. Not only dielectric constant, but also Q×f values are dependent on the densification of BST ceramics. 2. Design and construction of microwave ceramics dielectric filters Microwave dielectric properties of Ba(2-x)Sm(4+2x/3)Ti9O26 system (BST)(0.0≦x≦0.3 ) and design procedures of microwave coaxial dielectric bandpass filter have been investigated in this work. Dielectric coaxial resonators with excellent dielectric properties of εr =75∼80, Q×f value =11000 and great temperature stability at the resonant frequency. ( = ~ 0 ppm/℃)were used. Microwave badnpass filters for mobile communication system were constructed by using such coaxial resonators. Both air-gap coupling and direct coupling methods were applied as the coupling instruments in the transformation of electromagnetic energy. Comb-line theory was used to adjust the response of filters. The resonant frequency of each resonator, coupling coefficients between adjacent resonators, and external quality factor were adjusted to achieve the target specifications. The measured responses were in excellent agreement with the expected results.