Behavior of έ(ω) and tan δ for a class of low-loss materials

We report a study on the relaxation behavior of the real part of the permittivity. We also discuss the loss tangent of a class of materials in the microwave to millimeter band of frequencies. For relaxation response we show that the permittivity is a monotonic decreasing function of frequency. Also, for many low-loss ceramics, glasses, crystals, and solid polymers we found that the loss tangent increases nearly linearly with frequency. This linearity is explained in terms of the pulse-response function and the Sparks-King-Mills model. We show that the linearity may be used to extrapolate the loss tangent beyond the measurement band.