Balanced wave - impedance “hexaferrite” substrates for antenna miniaturisation

In this talk, Oliver James introduces balanced wave-impedance materials for use in antennas. Certain hexagonal ferrites fall into this class of materials, exhibiting the property of equal electric permittivity and magnetic permeability, giving the material the same wave impedance as free space. Such materials are claimed to give efficient impedance matching between the antenna substrate and the transmission medium, but is this effect more important than conventional antenna substrate performance characteristics such as material loss tangent? Oliver discusses a radiatively characterised antenna built on such a substrate and considers the impact of the choice of material on antenna miniaturisation as well as the potential for frequency tuning