Broadband Balance-to-Unbalance ( Balun ) Design

• Main Authors: Jhe-Ching Lyu, 呂哲慶
• Other Authors: Chi-Yang Chang
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/35571617266466281915

碩士 === 國立交通大學 === 電信工程系所 === 94 === 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.