基于Ba_xSr_(1-x)TiO_3薄膜电容的L波段可调滤波器

L-Band Tunable Filter Based on Ba_xSr_(1-x)TiO_3 Thin-Film Varactors

在蓝宝石基片上使用Ba_xSr_(1-x)TiO_3(BST)铁电薄膜电容作为可调元件制作出一种五阶梳状线可调带通滤波器。通过对BST平行板电容的材料特性(介电常数、损耗和可调率)的提取,其中40 V偏压下的可调率为43.1%,将这些特性运用于可调滤波器的制作。初步的实验结果分析表明,在20V直流偏置电压作用下,滤波器的中心频率从1.19GHz变化到1.31GHz(可调率为10.1%),带内插入损耗为13.5~13.7dB,回波损耗低于12dB。

A tunable fifth-order combline bandpass filter using thin-film Ba_xSr_(1-x)TiO_3(BST)varactors and fabricated on a sapphire substrate is presented in this paper.The voltage-dependent material properties(permittivity,loss tangent,and tunability)have been extracted and used in the development of a specific integrated metal-insulator-metal(MIM)capacitor that shows a measured tunability of 43.1% under 40 Vbias.After the BST parallel plate capacitors characterization,the varactors have been exploited in the design of the tunable combline bandpass filter.The analysis of some preliminary experimentalresults shows that the application of 20 Vbias varied the center frequency of the filter from 1.19 GHz to1.31 GHz which corresponds to a relative shift of 10.1%.The insertion loss varied from 13.7dB to 13.5dB,while the return loss was less than 12 dB over the bias range.