Analysis of the diversity potential of an intelligent quadrifilar helix antenna

Antenna diversity has been used as a method to mitigate multipath fading. For mobile communications, this has usually been at the base station, but there is an increasing demand for diversity antennas to be implemented at the mobile. In this case, there is often a main antenna, as in any other handset, and also a smaller diversity antenna. With such antennas, it is difficult for both to maintain high mean effective gain (MEG), which is a disadvantage to the overall system performance. Also, implementing more than two elements usually increases the handset volume. An intelligent quadrifilar helix antenna (IQHA) (see Leach, S.M. et al., IEE Proc. on Microwaves, Antennas and Propag., vol.147, no.3, p.219-23, 2000) is based on four helix antenna elements that can be combined to allow beam steering towards satellites and terrestrial base stations. Combining the elements in an appropriate fashion gives scope for a four-branch diversity system. The paper investigates why an IQHA provides good diversity potential. An IQHA is primarily an angular diversity system and it is shown that the equal gain combining (EGC) method (see Saunders, S.R., "Antennas and Propagation for Wireless Communication Systems", Wiley, 1999) provides the highest system gain since there is a significant increase in MEG. The analysis is carried out both for the standard sized IQHA and the reduced-size meandered IQHA.