Research And Design Of MIMO Antennas With High Isolation

With the rapid development of the wireless communication systems,rich multimedia services require higher and higher information transmission rates.Although spectrum utilization can be improved by traditional wireless communication systems which can use the better technologies,but the channel capacity is still limited a great deal of by the finite spectrum resources.In view of the fact that the channel capacity and the data transmission rate can be significantly increase by MIMO technology through multi-path effects and channel fading without adding additional spectrum resources,so it has a broad application prospect in 4G and 5G communication systems.MIMO antenna is one of the key components of MIMO system,with the development trend of miniaturization of mobile communication systems,the miniaturization of the antenna and isolation between cells becomes a key issue in MIMO antenna design.Therefore,the design of the miniaturized,high isolation MIMO antennas is the focus of this study.The research background of the MIMO technology is recommended in this thesis,and the research status at home and abroad are also described,several common decoupling techniques are summarized from the decoupling principle.In this thesis,the decoupling of the MIMO antennas are studied by using the method of floor slotting,loading of floor resonance branch and the reactive load dummy elements.Two miniaturization and high isolation MIMO antennas are obtained enevtually.Using the method of floor slotting and loading floor resonating branch to improve antenna element isolation of the first MIMO antenna.The MIMO antenna is mainly composed of two folded inverted-F antennas to reduce the overall size of the antenna system.On the premise of without increasing the overall profile size of the antenna,the high isolation is achieved by etching an inverted T-shaped slot and loading the resonance branch on the ground between the antenna elements for the lower band and the higher band,respectively.In addition,two U-slits are etched on the feedlines to achieve a better impedance matching in the 5 GHz frequency band.Finally,the MIMO antenna achieves the coverage of 2.37-2.53 GHz and 4.79-5.86 GHz,including the 2.4 GHz,5.2 GHz,and 5.8 GHz frequency bands of the WLAN system.The isolation between the two antenna elements in the entire operating frequency band is greater than 15 d B.Therefore,the antenna has the good radiation characteristics.The isolation of the second MIMO antenna has been improved significantly by using the reactive loads dummy elements.The MIMO antenna is composed of three linear planar monopole antennas.Based on the parasitic element decoupling method,a theoretical derivation of the reactive loads dummys element decoupling method for three-port MIMO antennas is presented from the perspective of antenna impedance.The reactive loads dummy elements have been introduced between the adjacent antenna elements,then the reactive loads have been tuned by using ADS simulation software to acquire the best isolation in the operating frequency band.Each element can be independently matched by using an open-circuited stub or a lumped element.Finally,the antenna operates in the 3.5 GHz band and the isolation between adjacent antenna elements is better than 30 d B in the required frequency band,so it also shows the high efficiency of this decoupling technology.