https://scholars.lib.ntu.edu.tw/handle/123456789/122903
標題: | 微型化與寬頻帶前向式方向耦合器之設計 Design of Miniaturized and Broadband Forward-Wave Directional Couplers |
作者: | 顏睿志 Yen, Jui-Chih |
關鍵字: | 寬頻帶;耦合線;方向耦合器;比例頻寬;微型化;週期性結構;慢波效應;broadband;coupled lines;directional couplers;fractional bandwidth;miniaturization;periodic structures;slow-wave effects | 公開日期: | 2012 | 摘要: | 方向耦合器已被廣泛地使用在多種微波及毫米波電路中,其主要的功能,在於將訊號做分波及合波的處理。方向耦合器能以各種不同的元件來實現。其中,利用耦合微帶線能設計出具有前向式耦合特性的方向耦合器,其耦合機制來自於奇模態和偶模態相位變化的差異,當此一相位差距愈大時,耦合量就愈高。然而,由於傳統的耦合微帶線其奇偶模態的相位常數差異並不大,因此,要實現高耦合量的前向式耦合器通常需要較長的耦合線段。此外,又由於傳統耦合微帶線其奇偶模態的相位差會隨頻率變化而呈現單調遞增的特性,這類耦合器的頻寬通常都很小。鑑於以上這些缺點,本論文主要致力於前向式方向耦合器的微型化以及寬頻帶之設計。 首先,在探討過耦合線方向耦合器的基本理論後,本論文提出一種新的微小化的技術。此種技術除了在微帶線上加上週期性的電容性負載之外,還另外埋入周期性的金屬片於介質中。藉由這些埋入的金屬片,能使微帶線上的電容性負載在奇模態和偶模態中具有大小不同的電容值,於是,便能增大奇偶模態之間的相位差距,而達到微小化的目的。而在理論分析方面,本論文依據所提出的結構建立了一精準的等效電路模型,藉此可以推導出其在奇模態和偶模態中的特性阻抗和電氣長度,同時,還能歸納出一套完整的設計流程。根據這種新的設計方法所設計出的0-dB及3-dB前向式方向耦合器,其電路大小分別只有0.39λg × 0.08λg 及0.20λg × 0.08λg。與文獻中的耦合器相比,本論文所提出的微型化技術能達到較小的電路尺寸。 除了方向耦合器的微小化之外,本論文還提出了另一新型的寬頻帶前向式方向耦合器。此一耦合電路是由一對耦合微帶線及週期性的Y字型接地金屬柱結構所組成。在奇偶模態的分析方面,此結構在兩個模態中皆能達到寬頻的阻抗匹配;更重要的是,藉由調整Y字型接地金屬柱結構的尺寸,其奇偶模態的相位差距在某一寬頻帶內能維持一固定值。根據上述這兩個特點,此種耦合電路能用來設計寬頻帶的前向式方向耦合器。在分析方面,本論文提出了一簡單的等效電路用以描述此新型態的耦合線在奇偶模態中的傳播特性,同時,還以此建立一套設計流程。利用此特殊的耦合電路所實現的0-dB及3-dB前向式方向耦合器,其比例頻寬可以分別達到79.2% 及62.5%。而這兩種耦合器的尺寸分別為2.02λg × 0.26λg 及 1.08λg × 0.28λg。與文獻中的前向式耦合器相比,這種新技術能達到較大的比例頻寬。 Directional couplers find numerous applications in microwave and millimeter wave circuits. The directional coupler using coupled microstrip lines has forward coupling due to the unequal electrical lengths of the even and odd modes along the lines. Conventional forward-wave directional couplers require long line length as a result of the small difference between the even- and odd-mode phase constants. Furthermore, since the phase difference between the two modes usually increases monotonically with frequency, the fractional bandwidth of this type of coupler is typically small. Therefore, the research of this thesis contains a miniaturization method to implement forward-wave couplers and a novel approach for broadband designs. In this thesis, after an overview of the basic theory, compact forward-wave directional couplers are proposed by using periodic capacitive loading with embedded patches. Owing to the presence of the embedded patches, the capacitive loadings have distinct equivalent capacitances of the even and odd modes, which makes the phase difference between the two modes enlarged. Therefore, the size of the proposed coupler can be significantly miniaturized. An equivalent model of the unit cell is constructed to predict the electrical lengths and the Bloch impedances for both the two modes. Moreover, a simple design procedure is provided. Based on this design methodology, a 0-dB coupler and a 3-dB coupler are designed with compact sizes of 0.39λg × 0.08λg and 0.20λg × 0.08λg, respectively. Compared with other previous works in related literature, this new idea can achieve a forward-wave directional coupler with more compact size. Next, in order to achieve broadband performances, the forward-wave directional couplers loaded with periodic Y-shaped ground via structures are proposed. Broadband impedance matching of the even and odd modes can be approximately achieved. The proposed coupler can provide an almost constant phase difference between the two modes over a wide frequency range. Therefore, a forward-wave coupler with a broad bandwidth can be expected. The Bloch impedances and the electrical lengths of both modes can be derived with the aid of the simple equivalent models. Also, a complete design procedure is presented. The fractional bandwidth of the proposed broadband 0-dB coupler and 3-dB coupler are 79.2% and 62.5%, respectively, and their circuit sizes are 2.02λg × 0.26λg and 1.08λg × 0.28λg, respectively. Compared with the other works in related literature, the proposed couplers possess superior broadband performances. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/252707 |
顯示於: | 電信工程學研究所 |
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ntu-101-R99942015-1.pdf | 23.32 kB | Adobe PDF | 檢視/開啟 |
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