Polarization Diversity for Base Station Antennas

The use of space diversity in the reception of mobile radio signals is a well known technique to mitigate fading and is implemented in most wireless systems of today. The motivation for these antennas is the reduced cost for installation and the smaller space needed using polarization diversity instead of the traditionally used space diversity. Further, in a mobile communication system, base station antennas with a nominal ±45° to vertical linear polarizations are preferred since they provide equal mean power on both antenna branches. Dual polarized antennas are traditionally characterized in terms of port-to-port isolation and co- and cross-polar patterns. However, in the current situation, we identify the critical parameter when the antenna is used as a sensor in a polarization diversity reception system. This turns out to be the far-field coupling between the two channels. Two types of antenna configurations are analyzed in this current situation, a dual polarized aperture coupled patch and a pair of slanted dipoles. The antennas are analyzed using both measured and simulated radiation patterns.