Broadband Measurement of Dielectric Constant on FR-4 PCB by Using Discontinuous Microstrip Lines

In this paper, we propose to investigate the use of the equivalent mode for the discontinuous microstrip lines to measure the dielectric constant of the substrate within the high-frequency printed circuit boards. Our planar-circuit non-resonant method of this project is based on standard two-port transmission/reflection methods and can be used to determine the effective dielectric constant over broadband frequencies. A simplified measurement formula is obtained by self-calibration using two different structures of microstrip lines, which can avoid more complicated calculations. Comparing to the previous work, we use a more accurate equivalent model for the discontinuous microstrip lines and the effect of dispersion on high frequency-microstrip lines are also considered in this method. The trace functions can be calculated from the calculations of the measurement results, and the dielectric constants will then be determined. The experimental setup of this method is easy to be implemented and low cost. According to my understanding, the measurement results are more accurate comparing to other methods. This measurement method for the dielectric constant can be adopted and used in the high-frequency laboratory with vector network analyzers.