超宽带Marchand巴伦分析与设计

Analysis and design of ultra-wideband Marchand balun

给出了多层Marchand巴伦的等效电路,在此基础上讨论了巴伦的结构参数对带宽的影响。结论表明提高巴伦结构中短路线的阻抗同时降低开路线阻抗可以提升巴伦相对带宽的上限。应用所得的结论设计了一款超宽带紧凑型Marchand巴伦。通过弧线形的弯折将巴伦的主体结构尺寸控制在0.1 λ_g×0.1 λ_g(λ_g为中心频率对应的波长)以内,同时在传输线之间加入接地线以减小巴伦输出端口的不平衡度。仿真结果表明,设计的巴伦在1.5~18.5 GHz内具有良好的回波损耗,同时在通带内具有±5°的相位不平衡度和±0.5 dB的幅度不平衡度,与理论推导结果吻合较好。

An equivalent circuit of multi-layer Marchand balun is given and the influence of structural parameters on bandwidth is discussed. It is concluded that the maximum relative bandwidth of balun can be expand through increasing the impedance of the short line and reducing the impedance of the open line. A compact ultra-wideband Marchand balun is designed based on the suggested conclusion. To reduce the size, the transmission lines of balun are folded within 0.1 λ_g×0.1 λ_g, and the imbalance between the output-ports is reduced through the ground lines between the transmission lines. The suggested balun achieved a great return loss within 1.5~18.5 GHz, the phase imbalance is within 5° and the amplitude imbalance is within 0.5 dB, which is in good agreement with the theoretical results.