Millimeter-wave open resonator-based dielectric characterization of printed circuit boards

In this work, a low-permittivity polymer rod-based open-resonator has been demonstrated for the dielectric characterization of some commonly used printed circuit board substrates at K
a
-band (26.5 GHz to 40 GHz). The concept of Fabry-Perot has been adapted at millimeter-wave frequency while ensuring a low-cost and robust design. First, the dielectric parameters and possible dielectric dispersion of the dielectric rod waveguide used in the open-resonator are investigated. This is done by fitting full-wave electromagnetic simulation results to the measured response. It is followed by introducing the test substrates into the resonant cavity of the open-resonator, thereby leading to an electromagnetic perturbation of the resonances. Finally, the dielectric parameters are extracted from the measured resonance frequency shifts for different test substrates. A wide range of relative permittivity is tested in the proposed setup, which features repeatability, considerable sensitivity to dielectric parameters, and relaxed assembly tolerances.