Diversity performance of the intelligent quadrifilar helix antenna in mobile satellite systems

An investigation, via measurement, is presented of the potential for using a quadrifilar helix antenna (QHA) as a diversity antenna within a mobile satellite communications environment where there is a non-line-of-sight (LOS) link between the satellite base station and the mobile. Received signals from the four elements of the QHA were collected at different sites, such that the effects of the presence of both buildings and trees were observed. Diversity gains of up to 14 dB relative to a standard QHA have been observed in areas where the signal is greatly shadowed. However, there is a penalty of up to 6 dB due to the noise from the extra receivers when using maximum ratio diversity combining within areas where the signals are not decorrelated, such as in LOS situations or in areas where there is little shadowing or multipath effect. A potential solution to the performance degradation in LOS situations is by applying complex weights to the signals and summing them prior to the receiver, rather than applying them after the receiver chain at baseband. However, there are complexity and cost penalties associated with this solution