Untersuchung und Realisierung von Mehrtorantennen zur Kanalkapazitätssteigerung von MIMO Systemen in Innenraumszenarien

The demand on very high data rates for future wireless communication systems, which until today are limited to several tenths of Mbit/s (e.g. Wireless Local Area Network for IEEE 802.11a with 54MBit/s) is growing. In order to overcome this problem, new multiple antenna systems (MIMO: Multiple Output Multiple I nput) are investigated and probably will replace the conventional single antenna systems, which use only one antenna element at the transmit and receive side, respectively. Deploying more antennas at both sides of a radio channel yields in a linear increase of the channels capacity to the number of the antenna elements used. Thus an optimized trade-off between spatial diversity and spatial multiplexing can be achieved. As a result of the higher diversity order, the signal quality is getting better even in cases of very large distances between transmit and receive antennas. Additionally, because of the spatial multiplexing, the required higher data rates can be also achieved. In both cases, independent of the enlargement of the data rates, the transmit power as well as the signal bandwidth could be held constant. MIMO-systems need both at the base and the mobile station a certain number of antenna elements. Therefore the goal of this work is the investigation and the realization of such antennas. It is known, that spatial multiplexing can be achieved, if identical (same polarization), spatial separated antennas are used. An alternative solution can be found on systems, which utilize the different polarization characteristics of the antennas. The great advantage of these antennas is their compact form, which is essential especially in the mobile terminals, and the independence of the antenna orientation, which is important for handheld devices. Therefore the deployment of antennas with orthogonal radiation patterns, evaluated by the radiation pattern correlation factor, is an elegant method to overcome the problems mentioned above. The first investigations have been made using simple dual-polarized antenna configurations and some advantages could be found. This fact has led to the extensive investigation of multiport antennas with more than two ports located as near as possible (ideally in the same place). The idea to investigate first a three-port and later on a four-port antenna has occured. The realized antennas, fulfil the following specifications which makes them a potential candidate for future MIMO Systems:• all ports are matched• low coupling between the Antenna ports• low radiation pattern correlation factor• satisfactory relative bandwidth of the return loss bettet than 10 dBFurthermore, more than one antenna structure has been investigated, to make the manufacturing easier and to cover as many as possible realisation possibilities. The question, why are these antennas a potential candidate for MIMO-systems, will be answered. The realized antennas will be investigated in different simulation scenarios and the yielded channel capacity of such MIMO-systems will be evaluated. This channel capacity will be compared with the channel capacity of identically polarized, spatially separated antennas such as half-wavelength Dipole or isotropic radiators of a certain polarization. In the conclusion, these results will be discussed. It is proven that the deployment of such multiport antennas yield in similar channel capacity values as the identically polarized antenna elements. Additionally, it is shown that the radio channels capacity depends strongly on properties of the examined indoor scenario, on the receiver position in the scenario as well as on the orientation of the antennas