Design And Performance Study On Multiple-antenna For Mobile Terminals

This dissertation focuses on the design of multiple-antenna for mobile terminals and the study of their performances in typical propagation environments.Starting with the utilization of space resource, MIMO technology has great potential in improving the system capacity. The development of wireless communications has targeted toward high-speed, high-quality, and multi-service. MIMO technology has been considered to be one of the promising solutions to resolve the bottleneck in increasing capacity. The crucial issue of a MIMO system is the exploitation and utilization of the multipath in the propagation environment. In most prior multiple-antenna designs that suitable for mobile terminals, several antenna elements were arranged together simply; additional structures for isolation improvement were needed when the mutual coupling between elements was high. The overall sizes of the designs were large, and the radiation charectersitics of antenna elements, like polarization and the shape of the pattern, exhibited weak complementary, which make the MIMO system unable to fully exploit the multipath in the environment.In this dissertation, in order to achieve dual polarization and complementary radiation patterns for hand-held mobile terminals, some compact multiple-antenna designs have been proposed. A compact dual-polarized antenna has been proposed, using a pair of inverted-L antennas fed by 180°out-of-phase excitations, together with a low-profile monopole. A compact feeding structure has been proposed, which combines a section of CPW and a 1/4 wavelength slot antenna. And then a planar dual-polarized antenna has been designed with the feeding structure. Both the two-element antennas have achieved dual-polarized radiation as well as highly complementary patterns, which means they can realize polarization and pattern diversity at the same time, while the isolation between the two ports remains high. Further, based on the planar dual-polarized antenna, a compact planar four-element antenna configuration has been presented, of which different elements can be combined to provide different diversity. For MIMO arrays on portable devices like laptop, a compact, low-profile multiband antenna element has been proposed. Parasitic branches with different resonant frequencies are designed to obtain wide bandwidths to cover the GSM850, GSM900, DCS and PCS frequency bands.Based on field measurement in typical indoor environment, this dissertation has made comparisons and discussions on MIMO systems employing antennas with different polarization and radiation patterns, with the planar four-element antenna as a representative. By assessing the channel capacity, received SNR, and correlation coefficient between elements at the receiver, it has been demonstrated that for terminal applications, complementary radition patterns along with mixed polarizations are more promising in preserving channel capacity. The obtained conclusion is helpful in achiving compact multiple-antenna design for mobile terminal devices.