寬頻與超寬頻微帶阻抗轉換器之設計

Abstract

本文研究由平行耦合線、傳輸線與短路殘段所設計的寬頻與超寬頻阻抗轉換器之設計，並以微帶線技術實現。此阻抗轉換器在通帶中有三個反射零點，透過傳輸線理論的分析，可以控制電路參數並調整反射零點的位置，達到增加頻寬且改善匹配效果。藉由電路的分析與設計方程式，可得電路的設計曲線。利用設計曲線，本文實作兩種阻抗轉換器。第一種寬頻轉換器的實作結果分別為 (A) 阻抗轉換比例1:2，反射損耗20 dB之比例頻寬為82%；(B) 阻抗轉換比例1:2，反射損耗30 dB之比例頻寬為68%；(C) 阻抗轉換比例1:2.8，反射損耗25 dB之比例頻寬為71%；電路面積皆小於λ/8×λ/8。第二種超寬頻轉換器實作結果分別為 (D) 阻抗轉換比例1:2，從3.1 ~ 10.6 GHz反射損耗低於15 dB；(E) 阻抗轉換比例1:4，從3.1 ~ 10.6 GHz反射損耗低於12 dB。量測與模擬的結果相當一致。

This thesis investigates design and analysis of compact impedance transformers consisting of a coupled-line section, a transmission line section and shorted quarter-wave stub for wideband and ultra-wideband applications. The proposed impedance transformers can be implemented by the microstrip technology. They are designed to have three reflection zeros within the passband. A wide bandwidth can be obtained for a wide range of transformed impedance ratios. The location of the reflection zeros can be tuned through the circuit parameters. Design curves of the transformers are plotted by solving the analytical equations. Using these curves, two kinds of microstrip impedance transformer has been implemented. The first wideband transformers are realized with (A) 1 : 2 impedance ratio with return loss better than 20 dB over a fractional bandwidth of 82%; (B) 1 : 2 impedance ratio with return loss better than 30 dB over a fractional bandwidth of 68%; (C) 1 : 2.8 impedance ratio with return loss better than 25 dB over a fractional bandwidth of 71%. Their circuit areas are all less than λ/8×λ/8. The second kind of transformer are realized with (D) 1 : 2 impedance ratio with return loss better than 15 dB over a frequency band from 3.1 to 10.6 GHz; (E) 1 : 4 impedance ratio with return loss better than 12 dB over a frequency band from 3.1 to 10.6 GHz. Good agreement between measured and simulation is obtained.