Evaluation of Effective Permittivity of Multilayer Strip-Line Structure with Air Layers Under Substrate Deformation and Prototype of Deformation Suppression Structure

Strip-lines consisting of layers of inhomogeneous substrates are widely used in high-speed transmission and high-frequency circuits such as coupled-lines and hybrid couplers. In such multilayer structures, mechanical deformation of the substrates due to external factors such as loading causes changes in the effective permittivity, which is a problem that causes degradation of signal transmission characteristics. In this study, we analyzed the relationship between substrate deformation and changes in electrical characteristics in an inhomogeneous strip-line structure by visualizing the pressure distribution between substrates and measuring the effective permittivity. Based on the analysis results, we proposed a structure to suppress substrate deformation and verified its effectiveness.