Complex Permittivity Measurements in a Wide Temperature Range for Printed Circuit Board Material Used in Millimeter Wave Band

This paper discusses the temperature dependence of the complex permittivity in the millimeter-wave band of dielectric materials used in printed circuit boards and its transmission loss effect. In the structure of a newly developed balanced-type circular disk resonator, two dielectric material samples sandwiching a thin circular copper disk can expand and contract under uniform pressure against temperature changes, which means the frequency dependence of the complex permittivity between 10 GHz and 95 GHz can be stably measured in a temperature range from -30°C to 130°C. To confirm the validity of measured values, a printed circuit board having a transmission line with a microstrip structure was fabricated, and transmission loss was measured at room temperature. Then, the dielectric material and the copper foil were taken out, the frequency dependence was measured, and the transmission loss of the transmission line was calculated by HFSS (three-dimensional electromagnetic field analysis solver) using these measured values. In the present model, transmission loss value calculated using the measured value is 10% closer to the measured value than that using the catalog value, and almost 96% of the measured values could be fitted. The frequency dependence of other dielectric materials was measured between 10 GHz and 95 GHz at temperatures of -30°C, 25°C, and 130°C. A difference of up to 0.57 dB/cm was obtained between the transmission loss calculated from the complex permittivity of the catalog value for 10 GHz at the temperature of 25°C and the transmission loss calculated from the measured value, confirming the effect of the temperature dependence of complex permittivity.