The advantages of coating a wire antenna with ferrite material, as opposed to dielectric material alone, have been demonstrated both theoretically and experimentally. It is established that apart from higher radiation efficiency and bandwidth, this material coating enables better control to be exerted over the antenna fields when placed close to the handset ground plane, and thus contributes to positioning an axial pattern null towards the head and having a very low SAR. This is unlike PIFA and meanderline antennas, which may have higher efficiencies in free-space but are greatly affected by their local environment and lead to reduced efficiencies and higher SAR values in the presence of the head.
Developmental simulation work translated the aforementioned attributes into a quad-band handset antenna design, which with a μ’ ~ 6.4 combined excellent band performance with high efficiency and a very low SAR. A tri-band antenna design was also developed (μ’ ~ 2) to explore the antenna’s potential with currently available ferrite material. Despite a drop in efficiency, the antenna behaved very satisfactorily both in terms of band coverage and SAR. It is concluded that the specific development of ferrite material that is more suitable for antenna applications, can lead to a commercially viable high efficiency and low SAR multiband handset antenna. |
