Coupled-Resonator Bandpass Filters and Their Applications

本論文分別提出具有寬截止帯與寬通帯之兩種耦合共振器帶通濾波器。此外,也利用耦合共振器帶通濾波器分別來實現一個寬通帯之雙工器與兩種三工器。這些帶通濾波器與多工器可運用於不同需求之無線通訊系統中。 在延伸截止帯方面,本研究提出共面波導饋入微帶線之帶通濾波器,其利用寬邊耦合電容性饋入耦合結構,分別放在輸入/輸出以及共振器之間來提供額外之開路殘段,藉此用於產生許多傳輸零點。隨著調整這些傳輸零點在數個不希望的諧波通帶上,而達到有效壓制倍頻效應而延伸截止帯的目的。 在增加比例頻寬方面,利用上板微帶線共振器與下板共面波導共振器之寬邊耦合的雙層結構,本文提出兩個近似橢圓響應之寬頻帶通濾波器。此外,利用寬邊耦合濾波器亦提出ㄧ個可設計之寬頻雙工器。 最後,為了克服三工器複雜設計之缺點,利用二分之一波長饋入之連接步階性阻抗共振器,來提出用於微帶線三工器上之新型匹配電路。在設計步驟上,利用此步階性阻抗共振器來設計匹配電路,要比傳統之三工器簡單許多。In this dissertation, two types of coupled-resonator bandpass filters (BPFs) with stopband extension and wider fractional bandwidth, respectively, are presented. In addition, coupled-resonator filters are also utilized for implementing a wideband diplexer and two triplexers, respectively. These BPFs and multiplexers can find applications in a variety of wireless communication systems. For the stopband extension, the Coplanar-waveguide(CPW)-fed microstrip bandpass filters, with broadside-coupled capacitive-tapped couplings at I/O and interstage resonators to provide extra open stubs for creating several transmission zeros, are proposed. By adjusting these transmission zeros to distribute around the spurious passbands, the stopband rejection may effectively be improved. For extending the fractional bandwidth, the broadside-coupled dual-plane structure, which has microstrip resonators on the top metal plane and CPW resonators on the bottom metal plane, is adopted to implement two quasi-elliptic coupled-resonator bandpass filters with wider fractional bandwidth. In addition, a wideband diplexer using the broadside-coupled filters is proposed along with the associated design concepts. Finally, in order to overcome the drawbacks of complicated design in triplexer structures, new matching circuits for microstrip triplexers are proposed based on half-wavelength tapped-connected (or fed) stepped-impedance resonators (SIRs). By using these matching circuits, the design procedure of the proposed triplexer structures is much simpler than the conventional ones.Abstract Chapter 1. Introduction 1 1-1 Research Motivation……………………………………………….1 1-2 Literature Survey…………….…………………………………….2 1-3 Contribution………….….……………………………...………….8 1-4 Chapter Outlines………….….…………………………………...10 Chapter 2. Coupled-Resonator Bandpass Filters and Stepped-Impedance Resonators 12 2-1 Insertion Loss Method………………………………….………...13 2-2 Lowpass Prototype Filters and Elements…….…..……………….15 2-2.1 Butterworth Lowpass Prototype Filters…………….…..…16 2-2.2 Chebyshev Lowpass Prototype Filters………………….....17 2-3 Frequency and Element Transformations………………..……….19 2-4 Impedance or Admittance Inverters……………………………....23 2-4.1 Filters with Impedance or Admittance Inverters…………..23 2-4.2 Practical Realization of Impedance and Admittance Inverters…………………………………………………………………25 2-5 General Principle for Coupled-Resonator………………………...26 2-5.1 Electric Coupling……………………………………...…..26 2-5.2 Magnetic Coupling………………………………………...28 2-5.3 Mixed Coupling…………………………………………...30 2-5.4 External Quality Factor Qe………………………………...32 2-6 Design of Coupled-Resonator Filters………………………….….34 2-6.1 Coupled-Resonator Filter………………………………….34 2-6.2 Cross-Coupled Resonator Filter…………………………...36 2-7 Stepped-Impedance Resonators (SIRs)…………………………...38 2-7.1 Resonance Properties of the SIRs…………………………38 2-7.2 Characteristics of SIRs…………………………………….40 2-7.3 Tapped-fed SIRs………………………………………...…41 2-8 Conclusion………………………………………………………..45 Chapter 3. Coplanar-Waveguide-Fed Microstrip Bandpass Filters With Multiple Spurious Suppression 59 3-1 Introduction………………………………………………………59 3-2 Second-Order Bandpass Filter…………………………………....61 3-2.1 Filter Structure…………………………………………….61 3-2.2 Filter Implementation and Results………………………...65 3-3 Fifth-Order Filter…………………………………………………67 3-3 Conclusion………………………………………………………..69 Chapter 4. Novel Broadside-Coupled Bandpass Filters and Their Applications 81 4-1 Introduction……………………………………………………….81 4-2 Broadside-Coupled Filter…………………………………………83 4-3 Stopband-Extended Broadside-Coupled Filter…………………...88 4-4 Wideband Diplexer……………………………………………….90 4-4.1 Diplexer Structure and Design………………………….....90 4-4.2 Diplexer Implementation and Results……………………..93 4-5 Conclusion………………………………………………………..95 Chapter 5. Design of Matching Circuits for Microstrip Triplexers 106 5-1 Introduction……………………………………………………...106 5-2 Matching Circuits for Triplexer………………………………....107 5-3 Modified Matching Circuits for Triplexer……………………....112 5-4 Conclusion…………………………………………………...….115 Chapter 6. Conclusions 126 6-1 Summary……………………………………………..………….126 6-2 Future Works………………………………………………….....129 References 130 Publication List 14