Research And Design Of Miniaturized High Isolation UWB MIMO Antennas

With the rapid development of wireless communication,people require more communication quality and high-speed rates.The multiple-input and multiple-output(MIMO)technique is proposed to improve the system capacity and reliability.Among them,a MIMO antenna is structured by loading multiple antenna elements in a system.Since the ultra-wideband(UWB)system has the disadvantage of multipath fading,the MIMO technology is introduced into the UWB system,thereby providing high-capacity and high-speed wireless communication.Most of the existing UWB MIMO antennas cannot combine miniaturization and high isolation performance,and the ground plane of multiple antenna elements is not shared.In this paper,the proposed UWB MIMO antennas with shared ground plane and high isolation are of great significance and application value.This thesis investigates the miniaturization and high isolation of UWB MIMO antennas with the following innovative work.The method to improve the isolation by loading parasitic branches increases the overall antenna design size and introduces the problem that most MIMO antennas do not share the ground plane.Based on the first UWB antenna designed,two-port and four-port MIMO antennas are proposed.The design method that contributes to the miniaturization of MIMO antennas using miniaturized antenna elements is achieved by placing the antenna elements,which are miniaturized using the curved flow technique,upside down on the same dielectric substrate.Three crossed X-shaped stubs are loaded between the ground planes of the two-port antenna to ensure the miniaturization of the antenna structure and the sharing of one ground plane while improving the isolation of the antenna.The two-port antenna is further extended to a four-port antenna with the same ground plane connection structure,verifying that this isolation structure is also applicable to the decoupling design of the four-port antenna.For the problem that the antenna elements in the MIMO antenna with diversity technique are placed orthogonally to each other,which increases the antenna size,a semicircular two-port MIMO antenna is proposed.By placing the antenna elements miniaturized by the half-parity technique upside down on the same dielectric substrate and using the inherent directional radiation characteristics of the two semicircular antenna elements,the antenna miniaturization is ensured while achieving higher isolation.For the problem that the adoption of defective ground structure will change the upper and lower bands of the antenna,a two-port MIMO antenna is proposed based on the second UWB antenna designed.By loading a stepped notch in the center of the ground plane of the seamlessly connected two semicircular antenna elements,higher isolation is achieved while ensuring the antenna’s upper and lower working bands.The two-port MIMO antenna consisting of the second miniaturized semicircular antenna element was expanded to an eight-port MIMO antenna with antenna elements placed orthogonally.The same ground plane connection structure with loaded cross-stubs is used.It is verified that such an isolation structure is also suitable for the decoupling design of an eight-port antenna.The simulation and measurement of the designed UWB MIMO antennas show that the designed MIMO antennas can achieve greater than 20 d B isolation in the UWB band.At the same time,the miniaturized size,good radiation characteristics,and envelope correlation coefficients that meet design requirements can be applied to modern MIMO communication systems,and related research provides theoretical support for their commercial application.The paper has 71 figures,4 tables and 95 references.