Printed circuit board permittivity measurement using waveguide and resonator rings

Knowing the frequency dependent complex permittivity of Printed Circuit Board (PCB) substrates is important in modern electronics. In this paper, two methods for measuring the permittivity are applied to the same Flame Resistant (FR4) substrate and the results are compared. The reference measurement is performed by inserting the sample in a rectangular waveguide and measuring the scattering parameters. The other measurement is performed by etching a microstrip ring resonator on the same substrate and measuring the scattering parameters. The results are similar and suggest isotropy and homogeneity.