Millimeter wave absorber using M-type hexagonal ferrite

Millimeter wave absorption properties of M-type hexagonal ferrite SrFe/sub 12-x/Al/sub x/O/sub 19/ composites have been investigated. The complex permittivity and permeability of the materials were measured by a free space method. When ferric ion was partially substituted by aluminum ion, the ferromagnetic resonance frequency moved up from 52 GHz to 83 GHz, corresponding to the increase of substitution amount: x=0 to 2. The result of material constant measurement was applied to the design of the impedance matched wave absorbers, and it was found that thin sheet absorbers for the V-band are possible using M-type hexagonal ferrite composites.