寬頻巴倫設計

Abstract

本篇論文利用傳統的印刷電路板製程，使用低介電係數(eps=3.38 )的微帶線設計了三種寬頻巴倫的架構。其中針對需要用到高偶模阻抗時，採用垂直安裝平面基板的結構來實現。針對兩個相同耦合線電路所組成的馬相巴倫介紹兩種設計方法，一為設計耦合量、另一為設計奇偶模阻抗，並且提供了1：2、1：4巴倫頻寬對應奇偶模阻抗曲線。以四分之一波長耦合線巴倫基礎來分析多節式阻抗轉換耦合線巴倫，在此也以奇偶模等效電路方法、微波網路分析來得到設計理論，並藉由串接多節耦合線來等效增加偶模阻抗，以便克制偶模訊號，得到寬頻巴倫特性；利用垂直安裝基板設計其中耦合線的偶模阻抗達到200 ，實作的巴倫具有100％頻寬，大小平衡1dB以內、相位平衡 。最後一寬頻巴倫前級使用衛更生等功率分配器，後級以開路與端路耦合線電路當作相位轉移的功能，得到頻寬大約120%，其大小平衡、相位平衡在1dB、+-10度以內。

This thesis presents three broadband balun designs which are fabricated on low dielectric substrates (eps=3.38 ) using conventional low cost PCB process. High even-mode impedances for coupled lines can be achieved by using Vertical Installed Planar ( VIP ) structures. The Marchand balun with two identical coupled lines can be designed using two methods: one is via the coupling, and the other is the even-odd mode impedances. Curves of the bandwidth versus the even-odd mode impedances for the 1:1 and 1:4 baluns are shown. The multisection impedance-transforming coupled-line baluns are analyzed by the quarter-wavelength coupled-line balun, and the design theory can be derived using the even-odd mode equivalent circuits and microwave network analysis. By cascading several coupled lines to increase the effective even-mode impedances, the even-mode excitations are rejected and the broadband baluns can be achieved. Using VIP coupled sections with even-mode impedance of 200Ω, the fabricated balun achieved 1-dB amplitude balance and phase balance over 100% bandwidth. The final broadband balun is consisted of a Wilkinson power divider and a pair of bandpass phase shifters. The amplitude and phase balanced are within 1dB and +-10 degree around 120% bandwidth, respectively.