The performance of polarization diversity antennas at 1800 MHz

Cellular radio systems have been in operation since the early 1970s and are experiencing tremendous growth. However, a major problem for cellular systems is the multipath, or short-term fading. One way to combat multipath fading on the uplink is to implement a diversity scheme at the base station. Until recently this was done by using two separate antennas positioned some distance apart from each other. The disadvantage with this method, however, is that the antennas have to be separated by several wavelengths to receive "independently fading" signals. Thus the antenna systems become large. With polarization diversity two antennas are also used but there is no need for any physical separation between them. Instead the two antennas are polarized in two orthogonal polarizations, e.g., horizontal/vertical or /spl plusmn/45 degrees slanted. In a study by Lotse et al. (see IEEE VTS 46th Vehicular Technology Conference Proceedings, vol.3, p.1643-46, 1996) it was found that space diversity yields typically about 1 dB better "diversity gain" than polarization diversity. However, how different antenna parameters affect the results has to our knowledge never been studied. The authors aim to fill this void.