Evaluation Of Multiple Antenna System In Compact Mobile Terminals

Research on multiple antenna systems has been a hot topic in recent years due to the demands for higher transmission rate and more reliable link in wireless communications. Using multiple antennas at both the transmitter side and the receiver side increases the channel capacity without additional frequency spectrum and transmit power. However, due to the limited space at the size-shrinking terminal devices, the most critical problem in designing multiple antennas is severe mutual coupling. The aim of this thesis is to provide compact, decoupled and efficient multiple antenna designs for terminal devices. At the same time, we propose simple and cost effective method in multiple antenna measurement. All those efforts contribute to the development of terminal devices for the fourth generation wireless communication.The background and theory of multiple antenna system are introduced first. Critical factors influencing the performance of multiple antennas are discussed, and the parameters to evaluate multiple antenna systems are analyzed in details. To design efficient multiple antenna systems, several decoupling methods, including defected ground plane, current localization and orthogonal polarization, are proposed. The working mechanism and design procedure of each method are introduced, and their effectivenesses are compared. Those methods can be applied to most of the terminal antennas, improving the isolation by6dB at least.In some special cases, especially at low frequency band below1GHz, the chassis of the device itself radiates like an antenna, which complicates the antenna decoupling. Thus, we extend general decoupling methods to the chassis excited cases. Based on characteristic mode analysis, two different solutions are provided, i.e., optimizing antenna location and creating orthogonal modes by using magnetic antenna. Those methods are applied to mobile phones, providing enhanced diversity and capacity performance.To design a good multiple antenna system, besides efficient decoupling, the performance of each single antenna is important. A miniaturized single antenna based on fractal structure is then developed. Frequency reconfigurable antenna is also designed, giving more flexibility to multiple antenna systems. All the efforts contribute to compact and efficient multiple antenna terminals.To measure the performance of a multiple antenna system, it is necessary to obtain the correlation coefficient. However, the traditional measurement technique, which requires the complex values of the electric field, is very expensive and time consuming. In this thesis, a more practical and convenient method is proposed. Fairly good accuracy is achieved when it is applied to various kinds of antennas.