  Polycrystalline samples of Z-type hexaferrites, having nominal compositions
$\mathrm{Ba_3Co_{2+x}Fe_{24-2x}M_xO_{41}}$ where M = $\mathrm{Ir^{4+}, Hf^{4+},
Mo^{4+}}$ and x=0 and 0.05, were processed via ceramic processing protocols in
pursuit of low magnetic and dielectric losses as well as equivalent
permittivity and permeability. Fine process control was conducted to ensure
optimal magnetic properties. Organic dispersants (i.e., isobutylene and maleic
anhydride) were employed to achieve maximum densities. Crystallographic
structure, characterized by X-ray diffraction, revealed that doping with
$\mathrm{Ir^{4+}, Hf^{4+}, Mo^{4+}}$ did not adversely affect the crystal
structure and phase purity of the Z-type hexaferrite. The measured microwave
and magnetic properties show that the resonant frequency shifts depending on
the specific dopant allowing for tunability of the operational frequency and
bandwidth. The frequency bandwidth in which permittivity and permeability are
very near equal (i.e., ~400 MHz for $\mathrm{Mo^{4+}}$ (x), where x=0.05
doping) is shown to occur at frequencies between 0.2 and 1.0 GHz depending on
dopant type. These results give rise to low loss at 650 MHz, with considerable
size reduction of an order of magnitude, while maintaining the characteristic
impedance of free space (i.e., 377 $\mathrm{\Omega}$). These results allow for
miniaturization and optimized band-pass performance of magnetodielectric
materials for communication devices such as antenna and radomes that can be
engineered to operate over desired frequency ranges using cost effective and
volumetric processing methodologies.
