An accurate measurement method of high permittivity materials by numerical analysis of coplanar waveguide

An accurate and simple technique for evaluation of high permittivity materials, (Bs,Sr) TiO₃ (BST) ceramics, in the microwave region is developed with assistance of full-wave analysis of a coplanar waveguide (CPW). S-parameters of the CPW are measured from 0.5 to 40 GHz, and effective permittivity and attenuation constants at each frequency are obtained from the S-parameter data. Relative permittivity (ε_r) and tanδ are evaluated by numerical calculations using the extended spectral domain approach taking the conductor thickness effect into consideration. The estimated ε_r's of Ba_0.7Sr_0.3TiO₃, Ba_0.5Sr_0.5TiO₃, and Ba_0.3Sr_0.7TiO₃ are 660, 1650, and 4450, respectively. The ε_r decreases slightly as frequency increased due to dielectric dispersion. This technique enables the evaluation of even a small deviation in high permittivity materials.