| Summary: | 博士 === 國立成功大學 === 電機工程學系碩博士班 === 95 === Due to the development in wireless communication was rapidly, how to design the high quality, to make the demands of the light and low cost devices is very important. In order to achieve miniaturization of the dimensions of the devices and for the system work with high efficiency and stability, many researches have been focusing on developing dielectric materials with high quality factor (Q×f), high dielectric constant (εr) and near zero temperature coefficient of resonant frequency (τf) for the use of dielectric resonator and microwave device substrate. Moreover, reduce the sintering temperature of dielectric materials are also become main studied. As mentioned above, the main research of this dissertation is divided three parts to study and discuss.
1. Development novel microwave ceramic material which has high dielectric constant, high-quality factor and microwave of high temperature stability:
(1) In the topic, the dielectric resonators of La(Co1/2Ti1/2)O3 system were prepared and studied. The dielectric constant values (εr) saturated at 29.8-30. The Q×f values of 34,000-67,000 (at 10 GHz) can be obtained when the sintering temperatures are in the range of 1410-1470oC. The temperature coefficient of resonant frequency τf was not sensitive to the sintering temperature. The εr value of 30, Q×f value of 67,000 (at 10 GHz) and τf value of -63.7 ppm/oC were obtained for La(Co1/2Ti1/2)O3 ceramics sintered at 1440oC for 6 h.
(2) The DRs of Nd(Co1/2Ti1/2)O3 system were prepared and investigated in this topic. The microwave dielectric properties and the microstructures of Nd(Co1/2Ti1/2)O3 ceramics prepared by conventional solid-state route have been studied. The prepared Nd(Co1/2Ti1/2)O3 exhibited a mixture of Co and Ti showing 1:1 order in the B-site. The εr value of 27, Q×f value of 140,000(at 9GHz) and τf value of -46 ppm/oC were obtained for Nd(Co1/2Ti1/2)O3 ceramics sintering at 1440oC for 4 h.
2. Effect of Additives on Microstructures and Microwave Dielectric Properties of A(Co1/2Ti1/2)O3 (A = La, Nd)Compositions:
(1) The dielectric properties of B2O3 and CuO doped La(Co1/2Ti1/2)O3 ceramics have been investigated. The optimum dielectric properties were obtained for La(Co1/2Ti1/2)O3 ceramics sintered at 1440oC for 6 h. However, the sintering temperatures of conventional microwave dielectric ceramics used for dielectric resonators, filters and other communication devices normally at 1200-1400oC. For practical applications, it is necessary to reduce the sintering temperature of La(Co1/2Ti1/2)O3 ceramics. Low melting glass addition is generally advantageous to reduce the sintering temperature of dielectric materials. In this dissertation, B2O3 and CuO were added to further lower the respective sintering temperature. A large sintering temperature reduction (about 100~200oC) can be achieved by adding B2O3 and CuO to the La(Co1/2Ti1/2)O3 ceramics.
(2) The crystalline phases, the microstructures and the microwave dielectric properties of B2O3 and CuO doped La(Co1/2Ti1/2)O3 ceramics were investigated. The εr value of 27, Q×f value of 140,000(at 9GHz) and τf value of -46 ppm/oC were obtained for Nd(Co1/2Ti1/2)O3 ceramics sintering at 1440oC for 4 h. B2O3 and CuO were added to lower the respective sintering temperature. With 0.75 wt% B2O3 addition, a dielectric constant of 27.2, a Q×f value of 153000 (GHz) and a τf value of 0 ppm/oC were obtained for Nd(Co1/2Ti1/2)O3 ceramics at 1320oC for 4 h, and higher than the dielectric properties of purity Nd(Co1/2Ti1/2)O3 ceramics. With 0.5 wt% CuO addition, a dielectric constant of 27.6, a Q×f value of 165000 (at 9 GHz) and τf value of -20 ppm/oC were obtained for Nd(Co1/2Ti1/2)O3 ceramics sintered at 1350oC for 4 h.
3. Design and Fabrication of Planar Monopole Antennas:
Two planar monopole antennas, one is crisscross monopole antenna and the other is a monopole antenna with a shorted parasitic element, for wireless system application have been investigated in this part. The impedance bandwidth changes significantly with varying the feed-gap. By tuning the feed gap height d between the ground plane and feed point, optimal wideband performance was obtained. The planar monopole antennas were also implemented and characteristics with normal planar monopole antennas were also investigated in different substrate materials.
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