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Effects of the human head on the radiation pattern performance of the quadrifilar helix antenna

The emerging satellite personal communication networks (SPCN) will offer global communication coverage based on small handheld terminals. Briefly, the requirement for the antenna system is to have a radiation pattern of defined shape in the elevation direction in order to fulfil a G/T requirement of around -23 dB/K in the receiving mode, circular polarisation, bandwidth of around 2 % and finally size appropriate for use on a compact handheld terminal. The quadrifilar helix antenna (QHA) is the most promising radiator for such an application because it offers a pattern which can be shaped in elevation as required with small structure changes, and circular polarisation due to its symmetric four-element structure and its phase quadrature feeding configuration. It is then important for the system designer to know the exact behaviour of this radiator when it is placed on different size terminals and near to the human body in order to evaluate the link performance. This article aims to show the effects of the human head and hand on the radiation pattern of the QHA. The radiation pattern shape and polarisation performance of the antenna system (antenna structure, feeding arrangement and mobile phone case) are examined through simulations and measurements.