Wireless communication is rapidly becoming the most popular solution to deliver voice and data services due to flexibility and mobility that can be offered at moderate infrastructure costs. Unfortunately, current wireless systems are unable to support some services offered by wire line systems due to the limited data rates achievable over wireless links. At the same time, there is a growing demand from the operators for better coverage to reduce infrastructure costs and enhance the wireless experience of the customers. One of the most promising solutions to overcome these issues is multiple-input multiple-output (MIMO) technology.
A Multiple-input multiple-output (MIMO) Antenna system is a well-known technique to enhance the performance of wireless communication systems. The channel capacity that a MIMO antenna system provides is much larger than that provided by the conventional wireless system.
The MIMO wireless technology uses multiple antennas at the transmitter and receiver to produce significant capacity gains over single-input single-output (SISO) systems using the same bandwidth and transmit power. It has been shown that the capacity of a MIMO system increases linearly with the number of antennas in the presence of a scattering-rich environment.
In spite of this advantage, the MIMO antenna system has many practical problems because the signal processing techniques do not consider the degradation of the correlation coefficients due to the coupling between antenna elements. Many researchers try to resolve the problem system-wise, or by using baseband algorithms and signal processing techniques. Therefore, to solve this problem and to operate the MIMO antenna system with properly, the characteristics of the MIMO antenna in real environment must be considered when developing processing algorithms. To implement a MIMO antenna system in real MIMO environment, we must consider the mutual coupling between MIMO antenna elements. Suppressing the coupling between antenna elements is an important problem in MIMO or multiple antenna systems because the coupling between the antenna elements influences the correlation coefficient in free space significantly.
This thesis describes several design techniques for MIMO antenna system having low mutual coupling between each antenna element. Two examples of the proposed models employed parasitic elements for mutual coupling suppression they show strong possibility of mutual coupling suppression between patch antenna elements to realize an independent channel for MIMO antenna system. It is proposed a compact 2-channel WiBro-MIMO antenna for the practical handy terminal. It is employed the projected (凸) ground structure for isolation between two antenna elements and it suppressed both of the mutual coupling and the radiation coupling. In addition, for the MIMO application, a ultra small and ultra wideband antenna having a novel antenna input impedance matching structure is proposed in this thesis.
The MIMO antenna design techniques proposed in this thesis are shown very low mutual coupling and very good antenna characteristics such as radiation pattern, antenna gain, resonable antenna size, etc.. Due to the these merits of the proposed design techniques, it is expected the proposed design techniques could be applied in the wireless communication system which is employed in MIMO system.