Orientation invariant diverstiy gain using transmit polarization diversity

Traditional polarization diversity systems have relied on the distribution of obstacles within the mobile medium to achieve signal decorrelation and power coupling between orthogonal polarizations. If the channel does not facilitate adequate power coupling, signal diversity is suboptimal because signal contribution from the polarization with lesser power is limited. Further, due to the presence of a dominant polarization, the signal power received in the orthogonal polarizations becomes a function of the transmitter orientation. The use of circular polarization at the transmitter is proposed to facilitate power coupling and alleviate the branch power imbalance between the vertical and horizontal polarizations. The analysis shows that if circular polarization is used, the branch power imbalance between the vertical and horizontal polarizations can be significantly lower than linear polarization, and that the cross polarization discrimination becomes independent of the transmitter orientation. The proposed antenna configuration to achieve circular polarization allows for polarization diversity to be implemented in the uplink and downlink.