基于微屏蔽线的140GHz低通滤波器研究

微屏蔽传输线是一种采用薄膜支撑的传输线结构，具有损耗小、阻抗可变范周大的特点。利用保角变换的方法对微屏蔽线单位长度的电容进行了分析，给出了单位电容值与相对介电常数、特征阻抗的关系。利用阶跃阻抗的结构．设计一个5阶的带内波纹为0．5dB、截止频率为140CHz的切比雪夫低通滤波器，并用HFSS仿真分析其传输特性，在滤波器的末端串联短接式短截线结构增强其带外抑制作用。

Research of 140GHz Low-pass Filter Based on Microshield Transmission Line

Microshield transmission line is a geometry supported by membrane,under which there is a metalized cavity.It has advantages like low loss and wide range of variable impedance.By Conformal Mapping Method,the capacitance per unit of microshield transmission line can be analyzed,and then the effective permittivity and impedance can be calculated.By means of the stepped-impedance structure,a 5-section Chebyshev low-pass filter with 140GHz cutoff frequency and 0.5dB ripples is designed.The transmission characteristic of the filter is simulated by HFSS,and the insertion loss of the filter is very low while the roll-off in the insertion loss is not sharp enough.A method by linking a short-end stub to the end of filter to improve the out-of-band rejection is analyzed.