Research On Compact Dual-polarized MIMO Antennas For Wireless Communications

Massive MIMO(massive Multiple Input Multiple Output)technology is used in the fifth-generation mobile communication network being deployed now.In the MIMO system,the diversity gain and multiplexing gain are mainly increased by increasing the number of antennas,thereby the communication quality and data transmission rate are improved.The number of antennas has increased,but the space of the base station is limited,which makes it necessary to consider shortening the distance between antenna units.The reduction in distance between units makes the mutual coupling between units stronger and affects the performance of the antennas.Therefore,the study of decoupling of MIMO antenna applied to base station system with compact spacing is extremely important and meaningful.Based on these,the decoupling method of dual-polarized base station array with compact spacing is mainly studied in this paper,and then this method is used to design dual-polarized MIMO antennas.The contents of each chapter in this thesis are summarized as follows:Chapter 1 firstly introduces the development of decoupling methods from two aspects,that are blocking the coupling path and constructing the inverted coupling path,and then summarizes the current research progress about dual-polarization MIMO antennas.Chapter 2 mainly introduces the related knowledge of MIMO technology and the decoupling principle of the decoupling surface method that will be used in the follow-up design.And then the improved calculation method of the pattern of the dual-polarized antenna is also given in this chapter.Chapter 3 describes the designed miniaturized broadband±45°dual-polarized antenna.The impedance bandwidth of the antenna is 630 MHz(2.26-2.89 GHz),the size of the radiating structure is 0.295₀?×0.295₀?(₀?is the free space wavelength at 2.6GHz),the gain within the bandwidth is stable within 6.0-7.1 d Bi,and low cross polarization is also achieved.Chapter 4 introduces the exploration of the decoupling method of the compact two-unit dual-polarized MIMO antenna.In this chapter,the designed dual-polarized antenna unit in Chapter 3 is used to form a two-element MIMO antenna with a center-to-center spacing of only 0.4₀?,and then this two-element MIMO antenna is used to explore the decoupling method.In the process of exploring decoupling methods,firstly the decoupling surface is used to reduce the co-polarization mutual coupling between the dual-polarized MIMO antenna elements,and obtain good effect.And then three kinds of parasitic structures are independently designed,the cross-polarization mutual coupling between the elements is also sharply reduced.Finally,the decoupling surface and the parasitic structure are combined to reduce the mutual coupling.The reduction of both the co-polarization mutual coupling and the cross-polarization mutual coupling demonstrates it is practicable to combine the decoupling surface and the parasitic structure.Chapter 5 describes the design of multi-unit compact dual-polarized MIMO antenna.In this chapter,the designed broadband dual-polarized antenna in Chapter 3 is used to develop into four-element MIMO antenna without decoupling structure firstly.Then,through using the decoupling method proposed in Chapter 4,a suitable decoupling structure is designed for the four-element dual-polarization MIMO antenna,and the MIMO antenna with compact spacing achieves good performance and high isolation.Within 2.45-2.75 GHz,the isolation is better than 18 d B and the Envelope Correlation Coefficient(ECC)is less than 0.0025 between all ports.This result shows the good diversity effect of the antenna.Finally,a 4×4 large-scale dual-polarized MIMO antenna is designed,and the feasibility of the proposed method applied to large-scale dual-polarized MIMO antenna is demonstrated.Chapter 6 summarizes the main contents of this thesis,and puts forward the current deficiencies and suggestions for further research.