Compact Dielectric Constant Characterization of Low-Loss Thin Dielectric Slabs With Microwave Reflection Measurement

A microwave reflection measurement method is proposed to determine the dielectric constant of dielectric slabs without knowing their exact thickness. The expression of dielectric constant is derived according to the transmission line theory, in which the loss of material is neglected. Error analysis for lossy dielectric slabs has also been conducted. In-house measurement results on commercial polymethyl methacrylate, polytetrafluoroethylene, and FR4 samples have been presented to validate the proposed method. Excellent agreement has been achieved between the proposed method and the conventional free-space method. The proposed method is suitable for the dielectric constant characterization of thin-slab materials with low loss and low dielectric constant.