The Design Of Reconfigurable Antenna For MIMO System

As one of the hottest research topics in the field of antenna, the reconfigurable antenna can significantly enhance the frequency resonant and radiation characteristics by changing the antenna radiator structure through electronic devices or using mechanical methods. Reconfigurable antenna can not only adapt to the fast and changeable wireless communication channels, but also can greatly reduce the number of antennas on the platform, Hence it has valuable applications in the future wireless communication system. In this thesis, we focus on the research of reconfigurable antenna and its application in MIMO system. The main achievements of this thesis are summarized as follows:Firstly, according to the principle that the operating frequency of the monopole antenna is closely related to its own physical length, a multi-band frequency reconfigurable antenna is designed, in which the monopole antennas with multiple resonant frequencies are integrated into the same dielectric substrate, and the radiation patch is connected to the switch. By controlling the state of the switch the operating frequency of the antenna can be changed, and therefore the frequency reconfigurable of the antenna can be achieved. In order to realize the miniaturization of the antenna, the Koch fractal structure of the antenna is loaded. On the basis of which, the proposed antenna makes up MIMO antenna array, and the simulation and test results reveal that the designed MIMO antenna has good port characteristics.Secondly, a planar printed Quasi-Yagi antenna is designed. In order to achieve a good impedance match, the modified ground structure is adopted and the structure of a microstrip line to the slot line is used to feed in the antenna. Furthermore, by arranging the antenna in vertical and horizontal way, a MIMO antenna array is designed. The simulation results show that the designed MIMO antenna array has a good impedance matching(|S11|<-10 d B) characteristics and a good isolation(|S12|<-15 d B) in the whole frequency band of 4.3-10.0GHz.Finally, a MIMO antenna for cognitive radio system is designed, which is composed of a reconfigurable filter and a stepped gradient ultra wideband antenna. A slot is etched in the upper part of the reconfigurable filter, and two separate PIN diodes are incorporated within the slot. By changing the state of these PIN diodes, the electrical length of the slot is changed. In this way, the bandpass filter can work at different frequencies. The working frequency of the stepped gradient UWB antenna can cover the entire frequency range of 3-10 GHz required by the cognitive radio system, thus spectrum sensing can be achieved. Simulation and experimental results show that the cognitive MIMO antenna has good isolations between adjacent antennas(|S12|<-15 d B).