在現代無線通訊系統中，濾波器（filter）在許多射頻與微波應用扮演著重要的角色。而面對新興的應用，使得濾波器除了須有好的特性外，還需要設計輕、薄、短、小，進而達到降低成本。在許多設計濾波器技術中，微帶線（microstrip）形式一直為設計者喜愛的方法之一，原因是它的製程容易，而且容易與其他被動和主動元件積體化。本論文利用傳統偶合線理論與彎折開迴路環形共振器（open-loop ring resonators, OLRRs）架構為基礎，將應用設計出雙工器（diplexer）、巴倫帶通濾波器（balun-bandpass filter）和巴倫雙工器（balun diplexer）。
首先，我們提出一個應用在 2.4/5.2 GHz 的雙工器，利用調整開迴路環形共振器（OLRRs）尺寸，可以調整雙工器之工作頻率。其設計頻率的插入損失（Insertion Loss）都小於 3 dB，且兩工作頻段間的衰減值可低於 25 dB 以上。第二為一創新而且簡單的巴倫濾波器，其工作頻率應用於 2.6 GHz。除了利用調整開迴路環形共振器（OLRRs）尺寸，可以調整巴倫濾波器之工作頻率，其平衡端的阻抗值也可藉由調整開路殘段（open stub）與平衡端微帶線的尺寸，可容易調整達到所需的阻抗值。其振幅比值可低於 2 dB，而相位差為180 ± 10∘。在共模抑制能力（common-mode suppression）可達 20 dB 以上。第三為一巴倫濾波器縮小化設計，且具有高共模抑制能力。其平衡端的阻抗值也可藉由調整開路殘段與平衡端微帶線的尺寸，可容易調整達到所需的阻抗值。其振幅比值可低於 0.4 dB，而相位差為180 ± 7∘在共模抑制能力（common-mode suppression）可達 25 dB 以上。第四為提供一簡單有效的方法設計一具有高隔離度與高共模抑制能力之頻率可調的巴倫雙工器，其頻率設計應用在 2.6 GHz和5.2 GHz。在低頻段中，其振幅比值可低於 0.2 dB，而相位差為180 ± 4∘；在低頻段中，其振幅比值可低於 0.3 dB，而相位差為180 ± 3∘。利用調整開迴路環形共振器（OLRRs）尺寸，可以達到頻率可調功能。兩工作頻段間的衰減值可低於 30 dB 以上，而且在共模抑制能力（common-mode suppression）可達 40 dB 以上。
本論文中，各種不同功能濾波器的實現，皆使用玻璃纖維（FR4）為基板，而基板上的導電材料為銅（Cu）箔。我們使用HFSS 電磁模擬軟體來進行參數調校與最佳化。論文中，所提出的各種濾波器在焊接SMA接頭後，以安捷倫 N5071C 網路分析儀進行量測。最後，由模擬與實測之結果顯示，本論文中所提出的各種濾波器，確實可以達到實用化之目的。

In modern wireless communication systems, filters play an important role in RF/microwave applications. New applications challenge RF/microwave filters with requirements for higher performance, smaller size, lighter weight, and lower cost. Among filter technologies, microstrip remains popular because it can be fabricated by photolithographic process and be easily integrated with other passive and active microwave devices. The main objective of this thesis is to explore a simple and effective structure based on traditional coupled-line theory and the configuration of folded open-loop ring resonators (OLRRs to design diplexer, balanced-to-unbalanced (balun)-bandpass filter (BPF) and balun diplexer.
This thesis covers four devices. First, a microstrip diplexer was proposed for 2.4/5.2 GHz applications. By adjusting the physical dimensions of the OLRRs, the center frequencies of the diplexer can be tuned separately over a wide range. The rejection between the two passbands is lower than 25 dB and the insertion loss for each band is lower than 3 dB. Second, a novel and simple single passband balun BPF is presented for 2.6 GHz applications. By adjusting the physical dimensions of the OLRRs, the center frequencies of the balun BPF can be tuned over a wide range. The balanced impedance is easily tuned by open stub and the width of the balanced microstrip. The amplitude difference is below 2 dB and the phase is within 180 ± 10∘for each operating band. The balun-bandpass filter presented excellent in-band balanced performance with common-mode rejection ratio more than 20 dB in the passbands. Third, a compact microstrip balun-bandpass filter with high common-mode suppression is presented. By tuning the sizes of the open stubs and the length of microstrip lines, the balanced impedance of the balun BPF can also be tuned. The amplitude difference is below 0.4 dB and the phase difference is within 180 ± 7∘at operating band. The simulated and measured common-mode suppression are both smaller than 25 dB within the operating bands of the two balun BPFs. Fourth, a simple and effective method for designing a frequency adjustable balun diplexer with high common-mode suppression and high isolation was presented for LTE (2.6 GHz) and WLAN (5.2 GHz) band applications. For low band, the amplitude difference is below 0.2 dB and the phase difference is within 180 ± 4o. For high band, the amplitude difference is below 0.3 dB and the phase difference is within 180 ± 3o. The two resonant frequencies of the balun diplexer are easily adjusted by changing the physical dimensions of the OLRRs. Rejection between the two passbands is lower than 40 dB and the common-mode suppression is smaller than 30 dB within the operating bands of two balun BPFs.
In this thesis, all designs were fabricated on an FR4 substrate and the electrode material was Cu foil. An electromagnetic simulator, Ansys HFSS, was used to adjust and optimize the associated parameters. The proposed filters are measured by Agilent N5071C network analyzer with SMA connectors welding. Finally, the simulated and measured results of proposed filters are in good agreement.

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