Μελέτη βελτιστοποίησης της αμοιβαίας σύζευξης μεταξύ στοιχείων κεραιών ΜΙΜΟ

Abstract

The last years, the rapidly increase and change in technology and its relevant services had as a consequence the parallel increase in demand of high data transmission capacity and high data rate, as well. In order for these demands to be fulfilled, the MIMO technology (Multiple – Input – Multiple – Output), which in fact is the evolution of an older mobile communication system which is called SISO (Single – Input – Single – Output), was implemented. A MIMO system presents the remarkable ability of simultaneously sending and receiving a large number of independent channels over the same radio channel, solving thus the problem of multipath propagation, in a satisfying degree. But, inspite of its advantages, the fact that the antennas in a MIMO system are placed in a densed proximity between them, in order to achieve the desired compact size which is essential for contemporary mobile appliances, can cause mutual coupling among the radiating elements. This phenomenon affects significantly the system overall performance by degrading antenna’s characteristics, and therefore it needs to be mitigated. The present dissertation under the title “Study on mutual coupling optimization between elements in MIMO antennas” concerns the investigation and analysis of MIMO systems, as well as the study of decoupling networks that lead to the reduction of the aforementioned coupling and the enhancement of the isolation between the radiating elements. Initially, there is a retrospection in the history of telecommunication systems. Afterwards, the logic and structure of MIMO systems are described, along with the way that these systems exploit the multipath phenomenon in order to achieve an increase in channel capacity. The channel transfer table which contains elements describing the channel's characteristics, is also defined. Then the advantages and disadvantages of MIMO systems are given, followed by a description of the phenomenon under study of mutual coupling and its reduction techniques, while each technique is explained by several recent examples found in modern literature. An essential part of this diplomatic MSc Thesis under the title “On reduction of Mutual Coupling Effect for Square Loop Antennas on a very Compact MIMO System”, in which my research regarding the design of a decoupling network and its results is shown. Finally, all the systems presented in this paper are compared and conclusions drawn from the whole are given.