具阻抗轉換特性之共面波導至帶線轉接

Abstract

為配合發展多層毫米波收發模組，本研究將研發多層共面波導至帶線轉接，作為單面型單晶微波積體電路與多層基板中內埋之被動元件間的電性連接，以建立相關無線收發模組之關鍵元組件技術。單面型傳輸線，如共面波導，擁有許多優於微帶線的特點，故常應用於單晶微波積體電路的研發；而帶線因為沒有輻射損耗，且可傳播TEM模態，非常適合於多層結構的被動元件設計。對於多層微波收發模組的應用而言，由於積體電路與多層基板的走線，其所在之平面不同，我們需要一精簡且低損耗的多層轉接器。本論文旨在討論共面波導至帶線轉接器的設計。 本論文所提出的共面波導至帶線轉接器之機制，主要由電磁耦合來實現，利用四分之ㄧ波長帶線開路共振器與四分之ㄧ波長槽線短路共振器，在共振頻率時，於兩者連接處有最大之耦合量，而能有效的由上層共面波導透過此電磁能量耦合傳至內層帶線。在多層電路的設計中，由於量測與連接外部電路的考量，常常需要使用連通柱(Via)來連接上下層金屬，以將訊號傳至表層。但在層數越多時，常常發生連通柱對不準，此製程誤差往往會造成高頻轉接頻率響應與阻抗匹配的偏移。由於本論文所提出之轉接器的主要電路不需使用連通柱，故可大幅降低因製程誤差所造成對電路特性的影響。 對於此轉接器，我們亦討論共面波導與帶線間基板厚度對電磁耦合量的影響，並轉換成等效電路中變壓器的圈數比，進而可使轉接器同時具有阻抗轉換器的效果。由於轉接器的阻抗轉換特性，吾人可利用線寬較寬的低阻抗帶線來設計多層基板中內埋的被動元件，進一步減小製程誤差對轉接器特性的影響，並將此轉接器應用於60GHz低溫共燒陶瓷無線收發機模組中的帶通濾波器設計。本論文所提之共面波導至帶線轉接器，具有寬頻且易於設計的優點，並可設計成符合所需之不同阻抗匹配，故適合應用於多層微波與毫米波收發模組的研發。

In order to cooperate with the development of multi-layered millimeter-wave transceiver module, the multi-layered coplanar-waveguide-to-stripline transition is proposed to facilitate the interconnection between uniplanar MMIC and embedded microwave passive components in the multi-layered substrate, so as to establish the key component technology for wireless transceiver modules. Uniplanar lines such as CPW has received increased attentions due to their merits over the conventional microstrip line. Therefore, it is widely used for MMIC designs. While Stripline features the advantages of no radiation loss and can support TEM mode, and is a very good candidate for embedded microwave passive component design in multi-layered substrate. Since the two transmission lines situate at different layers, implementation of compact and low-loss interconnections through the multi-layered substrate is of practical significance. In this study, a CPW-to-stripline transition is discussed and thoroughly investigated. The mechanism of the proposed transition is based on electromagnetic coupling between stripline quarter-wavelength open-stub and CPW quarter-wavelength short-stub. This transition design is capable of inducing strong coupling between CPW and stripline around the resonance frequency. As a result, the signal can be effectively transferred from upper CPW to embedded stripline through the electromagnetic coupling. In multi-layered circuit designs, vias are often used to transfer signals from the upper metal layer to the inner metal layer for the consideration of measurement and interconnection with other circuits. Misalignment of vias between layers could occur when more layers are used, which leads to shifts in transition frequency response and impedance matching, and becomes more serious as the operation frequency increases. Here, since the proposed transition requires no vias in the main circuit structure, we may reduce the shift in transition characteristic with fabrication error. For the proposed transition structure, the effect of substrate thickness between CPW and stripline on the amount of electromagnetic coupling is also investigated. The amount of coupling is represented by the transformer turn ratio in the equivalent-circuit model. As a result, the proposed transition also possesses the capability of impedance transformation. Based on the impedance-transforming property of proposed transition, one may employ low-impedance thus wider stripline for embedded microwave passive component designs, such that the sensitivity to fabrication error may be further reduced. The proposed transition is also applied to the design of bandpass filter in 60GHz low-temperature co-fired ceramic transceiver module. The proposed transitions have the advantages of wide bandwidth, low loss, and may be designed to provide impedance transformation between CPW and Stripline. They are attractive in implementing multi-layered microwave and millimeter-wave transceiver modules.