Study on an evaluation technique for millimeter-wave circuit substrate materials

在毫米波平面电路设计中，有必要对覆铜基板进行评估。应在毫米波频段测量绝缘子的相对介电常数和铜的表面电阻。电路基板的绝缘子大部分由夹层玻璃布片组成，其中含有低损耗塑料树脂。因此，由于介电性质的不同，其相对介电常数一般具有各向异性。然而，电路基板供应商在他们的目录中很少向我们展示各向异性介电常数的数据。电路设计者经常被测试电路或器件的测量结果与预计结果的不一致所困扰。另一方面，对于导体特性，需要评估绝缘体和铜膜之间的边界情况对其有效电导率的影响，以估计所设计电路的导体损耗。测量了一些介质衬底材料在50~75 GHz频段的各向异性相对介电常数。将平面方向相对介电常数的测量结果与截止柱面波导法的测量结果进行了比较。其次，我们研究了导体材料毫米波表面电阻的测量技术。

In design of millimeter-wave planar circuits, it is necessary to evaluate the copper-clad substrates. The relative permittivity of the insulator and the surface resistance of the copper should be measured at the millimeter-wave frequency band. Most of the insulator for the circuit substrate consist of the laminated glass-cloth sheets which are contained the low-loss plastic resin. Therefore, its relative permittivity has anisotropy generally for their dielectric properties. The circuit substrate suppliers, however, hardly show us data of the anisotropic permittivity in their catalog. The circuit designers frequently are troubled with the disagreement between the measured and pre-estimated results for the test-manufactured circuits or devices.On the other hand, for the conductor properties, the influence of the boundary situation between the insulator and the copper film on its effective conductivity should be evaluated to estimate the conductor loss of the designed circuits.In this study, we investigate a measurement method to evaluate the anisotropy of the relative permittivity of the dielectric laminate substrates using Whispering-Gallery mode dielectric resonator method, at first. Some dielectric substrate materials are measured in the 50 to 75 GHz band and the anisotropic relative permittivities are evaluated. The measured results of the relative permittivitiy in planar direction are compared with the measured results by the cut-off cylindrical wave guide method. Secondary, we investigate the measurement techniques to evaluate the millimeter-wave surface resistance of the conductor materials.