Ultrawideband Characterization of Complex Dielectric Constant of Planar Materials for 5G Applications

A broadband (1-35 GHz) time-/frequency-domain reflection technique for measuring the complex dielectric constant of low-loss dielectric slabs is presented. The technique uses a coplanar waveguide (CPW) transmission line sample holder for measurements. In addition to the standard substrate materials, the technique is suitable for the characterization of materials, such as glass, as it does not require complicated sample machining and preparation. The procedure is based on comparing the measured effective dielectric constant and the attenuation constants for both the loaded and unloaded CPW line sample holder. The effective dielectric constant and the attenuation constant are first modeled as a function of the real and imaginary parts of the superstrate's dielectric constant using a 2-D numerical line calculator. Samples under test are assumed to be nonmagnetic and have their material resonances at frequencies substantially above 35 GHz. The technique is validated through measurements of known Rogers RT/duroid samples. Measured complex dielectric constants of different materials are in very good agreement with data reported in materials' datasheets.