| The main concerns in wireless communications are the effects of multipath fading and interference. One way to reduce these effects is through the use of antenna diversity i.e. using more than one receiver antenna. Various diversity schemes has been investigate for use in wireless communications. In this dissertation, several diversity schemes for use in WLANs are studied. The antenna system for this use has to be inexpensive, compact size should perform well in the multi-path rich indoor environment.; A comparison between space and polarization diversity using λ/2 dipoles is reported in terms of signal-to-interference-plus-noise-ratio (SINR), correlation coefficient (ρ) and mean effective gain (MEG). The results indicate that a combined scheme of space and ±45° polarization diversity performs better than the others. Arrays using this combined scheme was analyzed for use on the PCMCIA card of a laptop computer. It was seen that a square lattice array had the smallest size (0.9λg x 0.9λg) and the best performance in terms of SINK, ρ and MEG.; The possibility of using this combined space and polarization scheme in multiple-input-multiple-output (MIMO) system was also explored. As expected, the correlation coefficient of MIMO channel was noticeably lower than that of SIMO channel, however the difference in correlation coefficient and capacity between the pure polarization diversity and the combined space and polarization diversity was not that significant.; Another arrangement consisting of a ring array of four Yagi antennas, each consisting of three-elements was considered. It was seen that a ring of radius 8.5 mm, giving an overall size of (0.59λg × 0.59λg), worked very well. This arrangement, combining angle, space and polarization diversity, is small enough to be placed on a PCMCIA card of a laptop computer and shows excellent performance in an indoor environment in terms of radiation pattern, correlation coefficient, mean effective gain and output SINR. |
