Methods for minimizing quadrifilar helix antenna interactions with the human head

The quadrifilar helix antenna (QHA) has been widely selected as a preferred handset antenna for mobile satellite communication. It has the key attributes of near-hemispherical pattern with good circular polarisation within a compact form-factor. Concern has been expressed, however, with regard to the impact of relatively high transmit powers on absorption in the human head. This paper studies this issue, and proposes methods for minimizing any effects. Two methods for minimizing these interactions have been studied by comparing the results of measurements and simulations. A simple homogenous sphere human head model with a dipole has been used to verify the specific absorption rate (SAR) predictions of the transmission line modelling method (TLM) against an analytic formulation, using dyadic Green´s functions. By moving the feed points of the QHA to the top end of the antenna and changing the radials at the opposite end, the peak SAR is reduced by around 12 dB. By moving the antenna up above the handheld case by around 9 cm, the peak SAR is reduced by 29 dB. The radiation patterns in each case are presented and compared with measurement