On correlations between dual-polarized base station antennas

Several diversity techniques employing multiple antennas in the base station have been developed for mobile communication systems. However, the performance of diversity methods strongly depends on the correlation between antenna elements. When multiple copolarized antennas are used in base station, the practical factor limiting the number of diversity branches is the required antenna separation, because large antenna separation makes the antenna array unfavourable large while small antenna separation may result in high correlations between the antennas. Therefore, dual-polarized antennas are commonly used to implement two diversity branches. If more than two diversity branches are needed, spatially separated dual-polarized antennas provide an attractive solution alternative. In this paper we propose a model for calculating the correlations between the cross and copolarized antennas when employing spatially separated dual-polarized antennas with nominal ±45° inclination to vertical linear polarization. Results are of theoretical nature and show the relationship between base station antenna correlations and the properties of the physical channel, base station, and mobile station antennas.