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 Nicolson-Ross-Weir (NRW) and Baker-Jarvis methods. This method does not require that the material under test (MUT) be centered into the air line, relieving stress on the measurement setup. The method is validated using air as the MUT and compared with different calibration methods. The SOLT and offset short technique are used with a Keysight 85058B calibration kit to extract the properties of RT/Duroid® 5880. The measurement results from 10 GHz to 67 GHz show ε
r
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.