以微波C形段設計雙頻阻抗轉換器

Abstract

本論文利用微波C形段(C- section)的傳輸線結構，設計雙頻阻抗轉換器，有效降低傳統二段傳輸線串聯設計之尺寸，其設計之方法可以透過奇模及偶模之分析再利用數值方法求解相關之參數。 本論文利用鋸齒耦合線結構，改善以微帶線實現微波C形段時，奇模與偶模的相位速度不一致的問題。因為奇模之相位速度大於偶模之相位速度，本文提出的方法就是在微波C形段的內圈加入鋸齒的結構，延長奇模的傳播路徑，以達到補償奇偶相位速度不一致的問題。 最後本文亦將此微波C形段之阻抗轉換器應用於雙頻濾波器的設計，藉由文獻上已知的參數，所製作的電路，量測與模擬的結果都相當一致。

A microwave C-section is used to contrive a dual-band impedance transformer. Based on the transmission-line theory, analysis equations are derived and design graphs are provided. On the basis of these design curves, structure parameters can be readily obtained. To tackle the difference of even- and odd-mode phase velocities of a microstrip C-section, a corrugated structure is employed. By properly tuning the structure parameters of a corrugated stage, excellent impedance matching can be achieved at the two designated bands. Two circuits designed at 2.5 GHz and 5.8 GHz with various termination impedances are realized and measured. The transformer is also applied to a dual-band bandpass filter design, based on the available data in literature. Good agreement between simulation and measurement results can be observed.