An efficient antenna configuration for base station polarisation diversity with reduced angular dependence

Polarisation diversity at base station sites offers the promise of low branch cross-correlations with much reduced antenna spacings compared to those required for simple spatial diversity. This is particularly important at lower frequencies where the spacings required must be small in order to be practical. Previously suggested configurations have suffered from the disadvantage of having branch correlations which depend strongly on the direction of the mobile being received. A three element configuration which overcomes this problem is presented. The configuration ensures that at least one pair of elements will have a usefully low cross-correlation for any value of received wave incidence angle, even when the crosspolarisation discrimination of the propagation environment is low. The effect of combining the signals from the elements using a maximal ratio combiner is calculated and the resulting signal statistics are shown to be almost independent of the direction of wave arrival, while providing a useful degree of diversity gain