Partially Filled Substrate Integrated Waveguide-Based Microwave Technique for Broadband Dielectric Characterization

Abstract

A novel partially filled substrate integrated waveguide (PFSIW)-based generalized microwave technique for broadband characterization of dielectric materials is presented. The proposed technique is based on the newly derived closed-form analytical formulation to extract the complex permittivity of test specimens placed in the PFSIW structure. The analytical formulations are further improved by developing an empirical model, which especially helps in extracting the loss tangent of the low-loss test specimen in the specified frequency band. The PFSIW structure along with appropriate planar microstrip transition section operating in the X-band region is designed using the full-wave electromagnetic solver, the CST-MWS. The designed substrate integrated waveguide (SIW) structure is fabricated on the commercially available FR-4 substrate, and accordingly, the S-parameters are measured under the unloaded condition which is in close agreement with the corresponding simulated data. Finally, a robust calibration methodology for the PFSIW structure is proposed by designing and fabricating a set of SIW calibration standards, which basically helps to translate the measured S-parameters to the sample interface by removing the effect of microstrip feed section. A number of standard planar RF substrates and dielectric specimens are measured using the designed PFSIW structure, and a close agreement between the extracted permittivity of these samples with their reference values shows the applicability of the proposed SIW technique.