Complex Permittivity and Permeability of Low-Temperature Sintered M-Type Barium Hexaferrite in Ka-Band Frequency Range

The magnetic permeability and dielectric permittivity of M-type barium hexaferrites (BaM) sintered at 920 °C with different additive amount of Bi₂O₃ are studied in Ka-band frequencies (26.5 ~ 40 GHz). The permeability and permittivity spectra of these low-temperature sintered BaM are determined for the first time in the millimeter-wave range due to their potential application in various millimeter-wave devices. The phases, microstructures and density have been also analyzed. The results show that there is not much difference in the permeability values, but the dielectric constant ε´ is improved from ~9 to ~18, with the increasing Bi₂O₃ amount from 0 to 5 wt%. Besides, much lower dielectric loss can be obtained with Bi₂O₃ content in the range of 2-3 wt%. These low-temperature sintered BaM exhibit lower dielectric loss at Ka-band frequencies compared with that sintered at high temperature.