Analysis of the Diversity Potential of an Intelligent Quadrifilar Helix Antenna

Antenna diversity has been used for many years as a method to mitigate multipath fading. For mobile communications, this has usually been conventionally at the base station, although there is an increasing demand for diversity antennas to be implemented at the mobile. The most common occurrence of this is in the Personal Digital Communications (PDC) network deployed in the Far East (1). Mobile handsets designed for this network often consist of a main antenna, like any other handset and also a smaller diversity antenna. Such a combination gives scope for a dual branch diversity system consisting of some spatial, angular and polarisation diversity (2). While such antennas may provide two signals with low correlation and similar signal to noise ratio, as required for diversity, it is difficult for them both to maintain high Mean Effective Gain (MEG), which is a disadvantage to the overall performance of the system. Further to this, implementing more than two elements is extremely difficult without increasing the handset volume, thereby limiting the maximum diversity gain achievable.