具低阻抗及強耦合之改良微帶線及被動元件之應用

Abstract

本論文首先提出一種新的低阻抗微帶線結構，在傳統的微帶線內部加入接地線，使得微帶線的特性阻抗值可以由在同一平面上的訊號線及接地線所控制，以此來提升微帶線的等效電容值，使得其特性阻抗值較同樣線寬的傳統微帶線為低，此種方式對於降低厚基板的特性阻抗值特別顯著，此外，我們也將訊號線加入至傳統微帶線的地，來更為降低微帶線的特性阻抗值，將此種微帶線結構應用在四分之一波長的步階阻抗諧振腔上，以此來製作對製程誤差較不敏感的小型化濾波器，同時也使得濾波器有更小的尺寸及較寬的上截止帶響應；接著，我們提出了數種可以提供強耦合量的微帶線耦合結構，分別將其應用在小型化的寬頻濾波器和單節及多節的3-dB方向耦合器上，雖然本論文所提出的電路結構需要有較多的導通孔，但是均可以使用標準的印刷電路板製程在一般的單層基板上完成，因此電路具有容易製作及低成本的優點。

This dissertation first proposes a novel low-impedance microstrip line structure. By inserting ground strips inside the conventional microstrip line, the characteristic impedance of the microstrip line can be controlled by the signal and ground strips in a coplanar manner. Compared to the conventional microstrip line with the same transverse width, the effective capacitance of the microstrip line increases so that the characteristic impedance decreases. The decreasing amount is particularly large for the thick substrate. In addition, we also insert signal strips in the microstrip ground plane to further decrease the characteristic impedance. The low-impedance microstrip line is applied in the quarter-wavelength stepped-impedance resonator. The designed filter can be insensitive to fabrication tolerances and have a smaller size and a wider upper stopband. Then, we propose several coupled microstrip line structures which can provide strong coupling. These tight-coupling structures are used to design miniaturized wideband bandpass filters and single- and multi-section 3-dB directional couplers. Although the proposed circuits need more via-holes, they can be easily fabricated on a single-layer substrate by the conventional printed circuit board (PCB) process with low cost.