非對稱共平面細耦合線的共模特徵

Common-Mode Characteristics of Asymmetrical Coplanar Thin-Coupled Lines

楊超舜

《國家奈米元件實驗室奈米通訊》 24卷4期 (2017/12) Pp. 22-26

摘要

對稱形的共平面波導已經普遍使用在電路設計；然而，實際電路佈局常有兩側接地面不等寬，亦即非對稱的狀況。本篇文章討論當三條平面金屬線其中兩相鄰細線分別供正電時的非對稱形共平面波導，其可視為激發在共模態的一種非對稱共平面細耦合線，並使用保角映射法去分析與得到共模態的特徵阻抗、埠特徵阻抗與等效介電常數。注意到對稱形三平面金屬線在偶/奇模態的埠特徵阻抗相等，特徵阻抗為埠特徵阻抗的一半/兩倍。然而非對稱型三平面金屬線的特徵阻抗與埠特徵阻抗並非如此簡單的關係，因此這裡稱作共/差模態。此篇文章探討提出的結構在共模態下特徵阻抗與埠特徵阻抗的關係，進而能做電路阻抗轉換之設計。

關鍵字

共平面耦合線 ； 非對稱形共平面波導 ； 共模態

並列摘要

The symmetrical coplanar waveguides have been commonly used for circuit design. However, the width of two-side ground planes is often not equal in the practical circuit layout; that is the asymmetrical condition. This article discusses the asymmetrical coplanar waveguide when two adjacent thin lines of the three planar metal lines are applied with the positive voltages, and it can be considered as an asymmetrical coplanar thin-coupled line in the common mode. Here, the conformal mapping technique is used to analysis the common-mode characteristic impedance, port-characteristic impedance and effective dielectric constant. It should be noted that the port-characteristic impedances of symmetrical three planar metal lines for even/odd mode are equal, and the characteristic impedance is half port-characteristic impedance in the even mode and double port-characteristic impedance in the odd mode. However, the relation between the characteristic impedance and the port-characteristic impedance of asymmetrical three planar lines is not simple, which refers to common mode and differential mode. The relation between characteristic impedance and port-characteristic impedance of the asymmetrical coplanar thin-coupled line in the common mode derived in this article can be used for impedance transformation of the circuit design.

並列關鍵字

Coplanar Coupled line ； Asymmetrical Coplanar Waveguide ； Common Mode