Reflected Group Delay of a Capacitively Coupled Resonator for Characterization of Dielectric Constant and Loss Tangent of Microstrip Substrates

This paper presents a novel method to determine dielectric constant and loss tangent of substrates used in microstrip circuits. The method is based on the reflected group delay of a microstrip resonator coupled to the input by means of an interdigital capacitor. The proposed method is first validated through simulations carried out using Advanced Design System by Keysight Technologies. The results obtained from simulations established that the proposed method can characterize the microstrip substrates having dielectric constant in the range of 1.8 to 7.2 at a loss tangent of <inline-formula> <tex-math notation="LaTeX">$4\times 10^{-4}$ </tex-math></inline-formula> with an error of less than 5% and 80% respectively. Final validation of the method is performed by the testing of Teflon and some standard boards from Rogers Corp. The error in the extracted values of dielectric constant and loss tangent of the boards used in testing are also found in agreement to the suggested values during simulation. Dielectric characterization of Acrylonitrile Butadiene Styrene (ABS) and Polylactic Acid (PLA) are also done to present a potential application of the proposed method in characterizing 3-D printing materials for microstrip applications.