Design of a Coplanar Sensor for RF Characterization of Thin Dielectric Samples

A multilayered conductor backed coplanar waveguide (MCCPW) sensor for the non-destructive characterization of thin dielectric samples in the RF and microwave frequency band is designed and developed. The newly designed sensor allows the measurement of complex permittivity of thin dielectric samples over a wide frequency band in a non-destructive way as it does not require any special sample preparation except for the fact that the surface of the test sample should be flat for good contact with the coplanar waveguide. The overall procedure is based on the measurement of scattering parameters of the test specimen placed at the top of the designed coplanar sensor in the specified frequency band using the vector network analyzer. The measured scattering data are then employed to compute the effective permittivity of the coplanar (MCCPW) structure using the revised form of the reflection-transmission approach. From the practical point of view, the advantage of the proposed technique is that it employs only two SMA to coplanar end launchers in lieu of the expensive microwave probe stations commonly being used in the past for carrying out such kinds of measurements. The applicability of the designed sensor is tested by extracting the permittivity of a number of reference samples from both the simulated and the experimental data.