Research And Design On Miniaturization Of MIMO Antennas For Wireless Communication Systems

As the rapid development of the wireless communication technology,on one hand,the requirements of the data transfer rate,communication quality and channel capacity are much higher;on the other hand,the volumes of wireless communication devices are getting smaller with more and more functions.As one of the the key technologies at wireless communication field,MIMO technology can enhance the channel capacity by times,resist the channel fading effects and improve the communication qulity without additional frequency resources and transmission power.The miniaturized MIMO antennas with high isolation guarantee the applications of the MIMO technology in the small size wireless communication devices.In the dissertation,a few miniaturized MIIMO antennas with high isolation for WLAN wireless communication system,mobile communication system and UWB wireless communication system are studied and designed.After simulating and anaylizing,these antennas are fabricated and tested.Good results are obtained.The main contents of this dissertation are as follows:1.A small dual-band dual-stripline MIMO antenna is studied and designed.This antenna using a bent planar monopole antenna and an extra coupling metal stripline to reduce the size and radiate the operating bandwidth;an I-shaped ground stub as the isolated structure is introduced to increase the isolation and improve the impedance bandwidth.The effects of the radiating part and the isolated structure are studied and analyzied.Good agreements between the simulation and the experiment are achived.It is demonstrated that this antenna is suitable for the WLAN wireless communication system.2.A miniturized dual-band microstrip slot MIMO antenna is studied and designed.By ectching an inverted L-shaped slot on the ground planar of a planar microstrip antenna to enhance the operating bandwidth,the proposed antenna is successfully miniaturized.Meanwhile,hight isolation is abatianed by using a rectangle slot as the isolated structure.The effects of the monopole antenna and slots on the MIMO antenna are discussed and the experiment results show that the performances of this MIMO antenna are good and it is suitable for the WLAN system.3.A polarization reconfigurable antenna is studied and designed.As the opertating bandwidth and axial ratio bandwidth are narrow for the normal polarization reconfigurable antennas,a stair-slots perturbed defected ground structure is proposed and studied.With the PIN diodes as the switches on the ground,the complexity of the design is greatly reduced without isolation network of the bias circuit.The measured results show that this antenna works at the frequency band of WLAN system and it can be reconfigurable among linar polarization state,left-hand polarization state and right-hand polarization state.Compared to the references,the impedance bandwidth and the axial ratio bandwidth are both greatly enhanced.4.A MIMO antenna for mobile application is studied and designed.This antenna is composed of a bent planar monopole and a shorted metal stripline which improves the working bandwidth.Two inverted C-shaped ground branches are studied and used as the isolated structure.The test results show that this antenna has wide impedance bandwidth and low coupling with a small size of the radiating part.It can be used for most 2G,3G,4G frequency bands and parts of other mobile communication system.5.A miniaturized triple band-notched UWB-MIMO antenna is studied and designed.After analyzing the effects of the half-cutting method on the miniaturization for UWB monopole antenna,a half-cutting UWB-MIMO antenna is designed.After studying the influence of the T-shaped ground isolated structure,the miniaturization and high isolation for the MIMO antenna are archieved.For the requirement of filtering function in UWB system,two slots are etched to get three notched bands.The simulated and measured results show that the three notched bands fully cover the target bands;while the good radiating performances of the proposed antenna also demonstrate that it is a good candidate for the UWB-MIMO system.