Exploitation of a novel magneto-dielectric substrate for miniaturization of wearable UHF antennas

A new magneto-dielectric material for wearable antenna applications at 868 MHz is presented. A barium–strontium hexaferrite is synthesized in order to achieve the best compromise between antenna dimensions and performances, exploiting the miniaturization properties offered by relative permeability greater than unity. The electrical properties of the substrate are then experimentally characterized and the corresponding material model is derived and used during the EM-simulation-based design of a patch antenna. The maximum antenna dimension is about λ/20 with a maximum directivity of 6.4 dBi. Broadband simulations and measurements of the reflection coefficient and of the radiated far-field are finally compared and demonstrate the reliability of the proposed design. A shielding solution by a conductive fabric allows to minimize back radiation and thus to avoid EM interference with human body tissues.

► Synthesis of a barium-strontium hexaferrite as planar antenna substrate.
► λ/20 miniaturization of the antenna, fully compatible with wearable applications.
► Radiation performance free of interactions with human body.
► 50 Ω broadband matching.