Broadband Measurement of Dielectric Properties of Substrates up to 67 GHz using a Coaxial Air Line

This paper presents a useful low-cost wideband dielectric characterization technique for packaging substrates using a coaxial air line technique up to 67 GHz. To the authors’ knowledge, this is the first demonstration of dielectric properties up to 67 GHz using coaxial air lines. The proposed method to extract the material properties is reference-plane-invariant (RPI) which combines NRW and Baker-Jarvis methods. This method does not require that the material under test (MUT) be centered in the air line, relieving stress on the measurement setup. The method is validated using air as the MUT and compared with different calibration methods. SOLT and Offset with a Keysight 85058B calibration kit is used to extract the properties of RT/Duroid® 5880. The measurement results from 10 GHz to 67 GHz show εr ranging from 2.16 to 2.22 and tanδ ranging from -0.002 to 0.006, excluding the Fabry-Perot resonance at 37.5 GHz.