| Ultra-wideband MIMO antenna has the advantages of wide working frequency band,high transmission rate,large channel capacity,and strong anti-interference ability,so it has been studied by a large number of scholars.This thesis mainly studies the miniaturization design,high isolation design and multi-notch design of the ultra-wideband MIMO antenna.In view of the above aspects,the main work of this thesis is as follows:1.A two-unit high-isolation ultra-wideband MIMO antenna based on a parasitic decoupling structure is proposed.First,the design analysis of the ultra-wideband antenna unit is introduced,the elliptical monopole is used as the radiating structure of the antenna.The radiating structure is slotted and the rectangular feeder is improved to a graded feeder,which improves the impedance matching of the antenna.Secondly,the port matching and port isolation of the ultra-wideband MIMO antenna array are simulated and analyzed,and the high isolation design is carried out on the basis of this antenna,and the influence of loading different parasitic branches on the decoupling effect is discussed.By loading T-shaped stubs and closed square loop stubs on the common ground of the antenna,the isolation of the antenna is better than 25 d B in the operating frequency range of 3.1-12 GHz,which is lower than the initial array without any decoupling structure.It is improved by nearly 10 d B over the whole frequency band.The designed antenna is manufactured and measured,and the simulation results are basically consistent with the measured results,which further illustrates the feasibility of the design.2.Based on the two-unit high-isolation ultra-wideband MIMO antenna,double-notch design research is carried out.By etching the C-shaped groove on the antenna's radiation structure,the antenna's notch design in the WLAN frequency band(5.1-5.8GHz)is realized;split ring resonators are loaded on both sides of the antenna feeder to realize the antenna in the Wimax frequency band(3.3-3.7GHz)notch design.3.An ultra-wideband planar spiral antenna array is proposed.First,the array antenna unit is studied in depth.Because the Archimedes spiral antenna has the advantages of compact structure,wide frequency band and radiating circularly polarized waves,it is used in electronic warfare and electronics.It is widely used in countermeasures,so the Archimedes spiral structure is selected as the radiation structure of the antenna unit,and its related radiation performance is analyzed.Considering that the planar spiral antenna is a balanced feed,and the coaxial is an unbalanced feed,a broadband balun is designed to solve the problem of unbalanced feed of the planar spiral antenna.In addition,planar spiral antennas usually radiate bidirectionally,a wave-absorbing material is used to fill the metal back cavity to achieve unidirectional radiation of the antenna.Secondly,the previously designed Archimedes plane spiral structure,broadband balun and reflective back cavity are combined to form the overall structure of the array antenna unit,and the simulation analysis shows that the antenna S11<-10 d B in the 6-18 GHz working frequency band.Then the array antenna elements are formed into a four-element ultra-wideband planar spiral transmitting and receiving antenna array,and the port characteristics and isolation between the elements are analyzed.4.Based on the four-unit ultra-wideband planar spiral transmitting and receiving antenna array,in order to further improve the isolation between the transmitting and receiving antennas,a three-dimensional hybrid metamaterial structure is proposed to reduce the spatial wave coupling between the array antennas.It is composed of a broadband wave-absorbing structure,a frequency selective surface,and a trapezoidal reflective splitter.By placing the structure between the transmitting and receiving array antennas,the circular polarization decoupling between the array antennas is realized and the isolation is greatly improved.In order to further verify the actual effect of the simulation design,the array antenna and the decoupling structure were processed separately and combined and tested,and the test results were basically consistent with the simulation structure. |
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