Circuit materials are evaluated by a number of different parameters, including dielectric constant (Dk) and dissipation factor (Df). Those two parameters also have temperature-based variants that provide insight into the expected behavior of a circuit material with changes in temperature, notably the thermal coefficient of dielectric constant (TCDk) and the thermal coefficient of dissipation factor (TCDf).
John Coonrod of Rogers Corporation provides technical advice and information about RF/microwave materials in this new Blog. The first posting reviews "FR-4 Versus High Frequency Laminates."