The effect of anisotropy field and saturation induction on phase shift at millimeter-wave frequencies has been examined for hexagonal ferrite materials. The analysis was done for both uniaxial and planar anisotropy at three particular frequencies of technological interest, 30, 60, and 90 GHz. The work was concerned primarily with materials; a simple thin slab device configuration was used for the analysis. Limitations on materials parameters due to propagation cutoff, phase error degradation over a specified bandwidth, and low field loss were also considered. The results indicate that any improvement in phase shift over conventional cubic ferrites will require a high saturation magnetization, comparable to that of Li-Zn ferrite, and moderate (6-10-kOe) to large (20-30-kOe) anisotropy fields, depending on the frequency.