寬頻微波系統之被動元件設計

Design of Passive Components for Wideband Microwave Systems

曾建臺(Chien-Tai Tseng)

指導教授 ： 湯敬文

國立中正大學/工學院/電機工程學系/博士(2014年)

摘要

在現代社會中無線微波系統已經被廣泛的應用。而手持式無線裝置更是經常的使用在日常生活中。因此，輕、薄、短、小、功能多、省電、價格便宜、速度快、美觀，將會是一個非常重要的趨勢。要達到此目的，所有的射頻電子零組件均已朝向多頻帶、多功能、高效能與低成本的方向邁進。在射頻收發模組中，關鍵的射頻零組件，如帶通濾波器、平衡至非平衡轉換器、耦合器，都是非常重要的功能性元件，均需具備寬頻帶及寬截止頻帶的電氣功能。因此本論文針對這三種關鍵零組件，做了深入的研究及探討。
本論文的第一部份是一具有寬截止頻帶的可調式帶通濾波器。此濾波器是由二個修正型耦合線及一個變容二極體負載殘斷所組成。當傳輸零點在頻帶的右邊時，量測時具有寬的可調範圍 0.95 – 1.55 GHz (48%)。而且具有可調的固定頻寬 120 MHz。在可調範圍內其插入損耗為 2.4 – 2.8 dB及返回損耗皆大於 20dB。
第二部份提出寬頻多階枝幹耦合器的設計。它是以各枝幹間的阻抗值關係為理論分析的基礎，並將此設計方法拓展至反射損耗頻寬上，使得擁有較低的最高阻抗值以方便電路的實作。在量測結果中比例頻寬(FBW)達70%，此外理論預測及量測間具有良好的一致性。
論文的第三個部份，是一新型寬截止頻帶的平衡至非平衡轉換器設計，此轉換器由二組步階式耦合線及兩段阻抗轉換器所構成。每一段耦合線的電氣長度都經過設計及優化並且兩兩串連，以達到最大的諧波抑制，而且，弱-強-弱步階式阻抗的耦合線，其諧波抑制的效果最顯著。最後模擬及量測比較圖可以發現其擁有良好的一致性。
第四個部份是一新型寬頻平衡至非平衡轉換器，此轉換器由寬頻功率分配器及180°相移器所組成。為了獲得更寬的操作頻帶，引入了修正型阻抗轉換器來設計平衡至非平衡轉換器。其設計實例為共平面波導(CPW)饋入的寬頻三階平衡至非平衡轉換器。最後模擬和量測結果均有良好的一致性。
本論文所提出的三種關鍵性零組件的電路架構與 PCB 具有高整合度。隨著射頻收發模組小型化與多工化的趨勢，本論文所提出來的帶通濾波器、平衡至非平衡轉換器、耦合器這三種關鍵零組件，將非常適合整合在現今無線通訊裝置的主機板上。

關鍵字

修正型阻抗轉換器 ； 平衡至非平衡轉換器 ； 步階式耦合線 ； 多階枝幹耦合器 ； 枝幹耦合器 ； 變容二極體 ； 修正型耦合線 ； 帶通濾波器 ； 寬頻

並列摘要

Wireless microwave systems have enormous impact on modern society. Moreover, the portable devices nowadays are widely adopted in daily life. Furthermore, small size, lighting weight, multiple functionalities, inexpensive cost, high-speed transmission, and beautiful appearance are the current trend. In addition, the RF passive components with multi-band, multi-functional, high-performance, and low cost have increased dramatically. Therefore, the wide passband and broad stopband performances are the main demanding of the passive components, such as filters, baluns, and couplers. In my dissertation, three key components of filters, baluns, and couplers have been proposed with detailed theory and design procedures.
The wide tuning range bandpass filter with a broad stopband is the first design. This filter is composed of two modified coupled lines and one varactor-loaded stub. In terms of measurement, the tunable bandpass filter with the transmission zero within the higher passband skirt has a very wide tuning range, from 0.95 to 1.55 GHz (48%). Moreover, with the return loss greater than 10 dB, there is a controllable constant passband bandwidth 120 MHz. Furthermore, within the tuning range, the insertion loss is from 2.4 to 2.8 dB and the return loss is greater than 20 dB.
The second design is the broadband 3-dB branch-line couplers. The detailed design equations for the branch-line coupler are provided as well. In order to obtain a wide passband, the multi-section branch-lines are utilizing for the proposed 3-dB microstrip branch-line coupler; in addition, the internal impedance levels of branch-line couplers can be reduced to fit the use of microstrip lines. Further, in terms of measured results, there is a wide bandwidth (greater than 70%). Good agreement between theoretical calculation and measurement validates the proposed method.
The third design is a novel wide stopband microstrip balun. The proposed balun is composed of a pair of stepped coupled line and two impedance transformer. The electrical length of each stepped-coupled-line stage is optimize and cascaded together for harmonic suppression. Moreover, the stepped coupled line with weak–strong– weak coupling results in a wide stopband. The agreement between theoretical prediction and measurement validates the proposed structure.
The forth design is the broadband balun. The broadband balun is composed of a wideband power divider and one 180° phase inverter. In order to obtain a broad operating band, the modified impedance transformers are adopted for balun design. A broadband three-stage balun with the coplanar waveguide (CPW) structure has been developed as design examples. Well-matched results of simulation and measurement can validate the proposed approach.
With the advantages of highly integration, four crucial components fabricated on printed circuit board (PCB) have been provided. The proposed filters, baluns, and couplers with compact size, multifunctional, and high performance have been realized, which are suitable for the integrated circuit of modern wireless communication.

並列關鍵字

multisectional branch-line coupler ； balun ； stepped coupled line ； broadband ； modified impedance transformer ； varactor ； branch-line coupler ； modified coupled line ； Bandpass filter

參考文獻

[1] M. Sanchez-Renedo, M. Gomez-Garcia, J. I. Alonso, and C. Briso-Rodriguez, “Tunable combline filter with continuous control of center frequency and bandwidth,” IEEE Trans. Microw. Theory Tech., vol. 53, no. 1, pp. 191–963, Jan. 2005.

[2] H. Joshi, H. H. Sigmarsson, S. Moon, D. Peroulis, and W. J. Chappell, “High-Q fully reconfigurable tunable bandpass filter,” IEEE Trans. Microw. Theory Tech., vol. 57, no. 12, pp. 3525–3533, Dec. 2009.

[3] V. Sekar, M. Armendariz, and K. Entesari, “A 1.2–1.6-GHz substrate- integrated-waveguide RF MEMS tunable filter,” IEEE Trans. Microw. Theory Tech., vol. 59, no. 4, pp. 866–876, Apr. 2011.

[4] C. Lugo and J. Papapolymerou, “Dual mode reconfigurable filter with asymmetrical transmission zeros and center frequency control,” IEEE Microw.Wireless Compon. Lett., vol. 16, no. 9, pp. 499–501, Sep. 2006.

[5] J. Nath, D. Ghosh, J.-P. Maria, A. I. Kingon, W. Fathelbab, P. D. Franzon, and M. B. Steer, “An electronically tunable microstrip bandpass filter using thin-film barium-strontium-titanate (BST) varactors,” IEEE Trans. Microw. Theory Tech., vol. 53, no. 9, pp. 2707–2712, Sep. 2005.