Radiation Efficiency Analysis of Balanced-Impedance Hexaferrite Substrate for Antenna Miniaturisation

Antenna miniaturisation in the low UHF band is required since the wavelengths are large compared to portable consumer terminals. Magneto-dielectric substrates such as hexaferrites which increase μ_r as well as ε_r have received attention for their miniaturisation potential, however there is a shortage of published results for the radiation efficiency of such antennas based on full 3D radiative characterisation in free space conditions. In this work, patch antennas fabricated on hexaferrite, FR-4 and RT5880 substrates were examined through simulation, fabrication and radiative measurement. While the frequency in hexaferrite was reduced by a factor of six compared to the RT5880 antennas, the efficiency in the hexaferrite antennas was low.
The combined effect of the losses in the hexaferrite and the electrically small size of the resulting patch antenna limits its use in long range transmitting applications, though it may still find application in short range or receiver applications