Extraction of Dielectric and Rough Conductor Loss of Printed Circuit Board Using Differential Method at Microwave Frequencies

A differential measurement technique for extracting the complex permittivity of substrate material and the effective conductivity of rough conductor surface is proposed in this paper. In this method, substrate integrated waveguide (SIW) cavity resonators having the same footprints and varied thicknesses are utilized to separate the conductor loss of the top and bottom surfaces of SIW cavity resonators. The extraction of effective conductivity from the surfaces of SIW cavities is done through examining the difference of unloaded Q-factors between the SIW cavity resonators with varied thicknesses. In advance of getting knowledge of the dielectric loss of substrate material, the conductor loss contributed by the metallic via array must be characterized. The separation between the conductor loss of metallic via array and dielectric loss of substrate material is done through the analysis and comparison of unloaded Q-factors between the SIW cavity resonators with the same length but different widths. In order to verify the proposed method, complex permittivity of a commercial substrate is measured with this method at microwave frequencies. The extracted dielectric properties of substrate material are generally consistent with that provided by the manufacturer.