Frequency-Dependent Qf Value of Microwave Dielectric Ceramics

The microwave dielectric properties of some typical low-loss dielectric ceramics (CaNdAlO4, Ba(Mg1/3Nb2/3)O-3, Ba(Zn1/3Nb2/3)O-3, Ba4Sm9.33Ti18O54, Ca0.71Nd0.26TiO3 and SrTiO3) were evaluated at different frequencies by using high-order TE0np resonant modes of resonant cavity method. The dielectric constant shows little dependence on frequency for these microwave dielectric ceramics, while the Qf value increases with frequency in the measurement frequency range of 3-14GHz. The results indicate that the Qf value as a frequency-independent constant at microwave frequencies is not valid for these microwave dielectric ceramics, while the constant Qf value has been accepted as a common recognition for a long period. The frequency dependence of Qf value is attributed to the defects-induced extrinsic dielectric loss, which cannot be avoided in actual microwave dielectric ceramics.