臺灣博碩士論文加值系統

微波介電共振器具有高介電常數、高品質因素及趨近於零的溫度頻率飄移係數等特性，適合用於介質共振天線、濾波器、震盪器和雙工器。近年來，由於微波通訊系統的演進及發展，微型化、高效能和低成本已經成為微波元件的主要需求。因此，高品質因素介電材料常應用於通訊系統中。由於具有低損耗的特性表現，也常設計於高效能微波元件上。然而，高介電常數陶瓷材料亦可達到微型化的目的，所以材料的選擇也是相當重要的課題。針對以上所述，本論文將以三個部分加以探討及研究：

一、高品質因素介質共振器之開發
[a]鈦酸鎂陶瓷之研究:
(1)二元的鈦酸鎂(Mg1.8Ti1.1O4)介電陶瓷擁有 er~15.7，Q×f~141,000 GHz，τf~–52.4 ppm/°C的微波介電特性，並且具有極低的介電損耗和低成本的特色，適用於全球衛星定位系統和無線區域網路上。因此，尖晶石結構的鈦酸鎂是非常值得研究及探討其微波介電性質。
(2)在本論文中，嘗試開發具有更高Q值的尖晶石陶瓷系統，分別利用Co或Zn部分取代Mg原子，可得到具有更佳微波介電特性的 (Mg0.95Co0.05)1.8Ti1.1O4 (Q×f~207,500 GHz)及(Mg0.94Zn0.06)1.8Ti1.1O4 (Q×f~210,700 GHz)。
(3)Mg1.8Ti1.1O4雖有極佳的Q×f值，但其共振頻率溫度飄移係數仍然為負值，無法有效運用於微波元件上。因此，予以加入具有正溫度飄移係數的陶瓷材料碳酸鈣(CaTiO3)，形成(1–x)Mg1.8Ti1.1O4–xCaTiO3陶瓷系統，以獲得具有高溫度穩定性的微波陶瓷材料。針對上述研究，並使用XRD、EDX及SEM來加以鑑定及分析。作為實際的應用，0.91Mg1.8Ti1.1O4–0.09CaTiO3陶瓷材料燒結在1330°C，持溫4小時，擁有良好的微波介電特性(er~19.6，Q×f~72,700 GHz，τf~–3.7 ppm/°C)，可以應用於微波介質共振天線上。

[b]鈦酸鋰陶瓷之研究:
(1)岩鹽結構的Li2MgTiO4 介電陶瓷是利用傳統的混合氧化物方法合成，透過SEM分析來觀察其表面微結構，並研究其微波介電特性。然而，陶瓷材料的燒結條件及晶體結構皆會影響其介電性質。在本論文中，一個新穎的微波介電材料Li2MgTiO4燒結在1360°C，擁有er~17.3，Q×f~97,300 GHz，τf~–27.2 ppm/°C的微波介電特性。
(2)(1–x)Li2TiO3–xZnO (x = 0.1–0.5)陶瓷系統是利用傳統的混合氧化物方法合成，透過XRD分析來作為相的鑑定、SEM分析來觀察其表面微結構，並研究其微波介電特性。然而，陶瓷材料的緻密化及表面微結構皆會影響其介電性質。除此之外，Q×f降低的原因，由於高比例ZnO添加量(x 〉 0.3)，將使得超晶格繞射面(002)的強度下降，且晶體結構將會轉變為無序化排列的岩鹽結構。作為實際的應用，一個新穎的0.7Li2TiO3–0.3ZnO陶瓷材料擁有良好的微波介電特性(er~23，Q×f~99,800 GHz，τf~0 ppm/°C)，可以應用於微波介質共振天線上。在本論文中，將設計與製造一個低損耗隙縫耦合介電共振天線，並研究其微波特性表現。

二、高介電常數微波材料之研究
高介電常數和低損耗(1–x)Ca4MgNb2TiO12–xCaTiO3陶瓷系統是利用傳統的固態反應法合成，透過XRD分析來作為相的鑑定並測量晶格參數的變化。當添加比例x = 0.1–0.9時，晶格參數呈線性變化，分別為a = 5.5478 Å、b = 7.7710 Å和 c = 5.4543 Å 下降至a = 5.4718 Å、b = 7.6799 Å和 c = 5.4262 Å。而且，當添加比例x = 0.3時，具有一趨近於零的τf 值(~–6.9 ppm/°C)，低損耗的Q×f 值(~20,200 GHz)及較高的介電常數(er~ 43.9)值。

三、微波介質共振天線之設計與製作
一個新穎的三頻介質共振天線(簡稱為DRA)，是由一高介電常數之介質共振器放置於FR4纖維基板上，並透過50 Ω的共平面波導(簡稱CPW)傳輸線饋入而組成。為了達到寬頻的應用，天線使用兩段寄生倒L型的微帶線產生兩個共振頻率，並覆蓋於3.5和5.2 GHz。最後，測量結果顯示，介質共振天線覆蓋的頻率範圍為2.30–2.72，3.45–3.61和 5.05–6.23 GHz，可以應用於無線通訊系統上。在本論文中，模擬與實作結果之頻率響應也呈現一致性。除此之外，良好的天線增益，輻射效率和輻射場型也將於論文中詳細敘述及討論。

The microwave dielectric resonators (DR) having a high dielectric constant, high quality factor and near-zero temperature coefficient of resonant frequency and other features, suitable for a dielectric resonator antennas, filters, oscillators, and duplexers. In recent years, due to the evolution and development of microwave communication system, miniaturized, high performance and low cost has become the main demand of the microwave components. Therefore, the high quality factor dielectric material often used in communications systems. With low loss characteristics performance, often designed for high-performance microwave components. However, the high dielectric constant ceramic material can also achieve the purpose of miniaturization, so the choice of material is also a very important issue. As mentioned above, the main study of this dissertation is divided three parts which preparation of high dielectric constant, high quality factor, design and fabrication of the microwave dielectric resonator antennas.

1.Development of High Q Microwave Dielectric Materials
[a]Study of Mg1.8Ti1.1O4 Ceramics:
(1)Binary titanate microwave dielectric ceramic Mg1.8Ti1.1O4 (er~ 15.7, Q×f~141,000 GHz at 10.57 GHz, and τf~–52.4 ppm/°C), having an extremely low dielectric loss and a low cost, were reported as suitable materials for global positioning system (GPS) and wireless local area network (WLAN). Therefore, the spinel-structured Mg1.8Ti1.1O4 is worthy to investigate its microwave properties.
(2)In this dissertation, with partial replacement of Mg by Co or Zn, the Q×f of the dielectrics (Mg0.95Co0.05)1.8Ti1.1O4 (er~ 16.1, Q×f~207,500 GHz at 10.72 GHz, and τf~–52.6 ppm/°C) and (Mg0.94Zn0.06)1.8Ti1.1O4 (er~16.5, Q×f~210,700 GHz at 10.52 GHz, and τf~–62.3 ppm/°C) can be easily boosted to a value higher than 200,000 GHz and retain compatible and τf.
(3)In order to achieve temperature-stable materials, CaTiO3 was added to form the (1–x) Mg1.8Ti1.1O4–xCaTiO3 ceramic system. A three-phase system was confined by X-ray diffraction patterns and EDX analysis. The microstructures of the ceramics were characterized by SEM. The microwave dielectric properties of the ceramics can be effectively controlled by varying the x value. For practical applications, a fine combination of microwave dielectric properties (er~19.6, Q×f~72,700 GHz at 9.03 GHz, τf~–3.7 ppm/°C) was achieved for 0.91Mg1.8Ti1.1O4–0.09CaTiO3 ceramics sintered at 1330°C for 4 h, which makes it is a very promising candidate material for applications in dielectric resonator antenna.

[b]Study of Li2TiO3 Ceramics:
(1)Development of Li2MgTiO4 Ceramics
Rock-salt-structured Li2MgTiO4 ceramic was prepared by the conventional mixed oxide route and its microwave dielectric properties were investigated. The microstructures of the ceramics were characterized by SEM. The dielectric properties of the ceramics exhibited a significant dependence on the sintering condition and crystal structure. A new microwave dielectric material, Li2MgTiO4 sintered at 1360°C has a dielectric constant (er) of ~17.3, a Q×f of ~97,300 GHz (where f = 9.86 GHz, is the resonant frequency) and a τf of ~–27.2 ppm/°C. The microwave dielectric properties of the ceramic are reported for the first time.
(2)Partial replacement of Li2TiO3 by ZnO
The microwave dielectric properties of the (1–x)Li2TiO3–xZnO (x = 0.1–0.5) ceramic system prepared by mixed oxide route have been investigated. The rock-salt structured (1–x)Li2TiO3–xZnO were confirmed by using X-ray diffraction spectra, scanning electron microcopy (SEM). The dielectric properties are strongly dependent on the compositions, the densifications and the microstructures of the specimens. The decrease of Q×f value at high-level ZnO addition (x 〉 0.3) was owing to the intensity of the (002) superstructure reflection decreased and became disordered rock-salt structure. For practical applications, a new microwave dielectric material 0.7Li2TiO3–0.3ZnO is suggested and it possesses a good combination of dielectric properties with an er of ~ 23, a Q×f of ~99,800 GHz (measured at 8.91 GHz), and a τf of ~0 ppm/°C. A low-loss dielectric resonant antenna using aperture-coupled cylindrical dielectric resonant was designed and fabricated using the proposed dielectric to study its performance.

2.Research of High K Microwave Dielectric Materials
High-dielectric-constant and low-loss ceramics in (1–x)Ca4MgNb2TiO12–xCaTiO3 system have been prepared by the conventional solid-state route. The forming of complete (1–x)Ca4MgNb2TiO12–xCaTiO3 solid solutions were confirmed by the X-ray diffraction pattern analysis and the measured lattice parameters,which linearly varied from a = 5.5478 Å, b = 7.7710 Å, and c = 5.4543 Å for x = 0.1 to a = 5.4718 Å, b = 7.6799 Å, and c = 5.4262 Å for x = 0.9. By increasing x, not only could the τf of the ceramics be turned to a near-zero value (~ –6.9 ppm/°C) at x = 0.3, a substantial Q×f (~ 20,200 GHz) and er (~ 43.9) could aslo be achieved simultaneously.

3. Design and Fabrication of Microwave Dielectric Resonator Antennas
A new triple-band dielectric resonator antenna (DRA) fed by a coplanar waveguide (CPW) is presented. The proposed antenna, composed of a high permittivity dielectric resonator and printed on FR4 substrate, is fed by a 50 Ω coplanar waveguide transmission line. In order to achieve wideband applications, the antenna with two parasitic inverted-L strips is demonstrated to generate two resonant frequencies covering 3.5- and 5.2-GHz. The measured results show that the antenna covers the frequency bands 2.30–2.72, 3.45–3.61, and 5.05–6.23 GHz with less than –10 dB of S11. The frequency response of the simulation results shows good agreement with the measured data. Good antenna gain, radiation efficiency and radiation patterns of the proposed antenna have also been observed across the operation band. Details of the proposed antenna design and experimental results are presented and discussed.

Abstract I
Contents XII
Table Captions XIV
Figure Captions XVI
Chapter 1 Introduction 1
Chapter 2 Theory 8
2-1 Theory of Microwave Dielectric Properties 8
2-2 Measurement of Dielectric Resonator 11
2-3 Basic Theory of Microwave Dielectric Resonator Antenna 12
2-3-1 Overview of dielectric resonator antenna 13
2-3-2 Characteristics of the cylindrical dielectric resonator antenna 14
2-3-2-1 A resonant frequency and quality factor 14
2-3-2-2 Near-field of the dielectric resonator antenna 22
2-3-2-3 Far-field of the dielectric resonator antenna 26
Chapter 3 Development of High Q Microwave Dielectric Materials 28
3-1 Mg1.8Ti1.1O4 Ceramics 28
3-1-1 Introduction 28
3-1-2 Experimental Procedures 30
3-1-3 Results and Discussion 32
3-1-3-1 Mg1.8Ti1.1O4 Ceramics 32
3-1-3-2 (1–x)Mg1.8Ti1.1O4–xCaTiO3 Ceramic System 37
3-1-3-3 Partial Replacement of Mg2+ by Co2+ in Mg1.8Ti1.1O4 Ceramics 45
3-1-3-4 Partial Replacement of Mg2+ by Zn2+ in Mg1.8Ti1.1O4 Ceramics 53
Chapter 4 Dielectric Properties of Rock Salt Li2MgTiO4 Ceramics at Microwave Frequency 63
4-1 Introduction 63
4-2 Experimental Procedures 63
4-3 Results and Discussion 65
Chapter 5 High-Q Dielectrics Using ZnO-Modified Li2TiO3 Ceramics for Microwave Applications 70
5-1 Introduction 70
5-2 Experimental Procedures 71
5-3 Results and Discussion 73
Chapter 6 Structure, Dielectric Properties and Applications of CaTiO3-Modified Ca4MgNb2TiO12 Ceramics at Microwave Frequency 86
6-1 Introduction 86
6-2 Experimental Procedures 87
6-3 Results and Discussion 88
Chapter 7 Wideband CPW-Fed Dielectric Resonator Antenna with Parasitic Inverted-L Strips for Wireless Communication Applications 96
7-1 Introduction 96
7-2 Antenna description 97
7-3 Results and discussions 100
Chapter 8 Conclusions 107
References 111
Publication List 122

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