| The fifth generation mobile communication technology(5G)is booming,and the antenna is an indispensable device,which performance will affect the quality of the communication system.In order to meet the development needs of 5G communication technology,multiple-input multiple-output(MIMO)antennas are widely used due to their ability to solve signal multipath fading,improve channel capacity and spectrum utilization.The characteristics of miniaturization,multi-band,and high gain are the core directions of antenna development.But in MIMO antennas,miniaturization and high isolation are contradictory.This is a challenge,so this thesis focuses on the miniaturization,isolation and multi-band of MIMO antennas in the Sub-6 GHz(3.3～3.6 GHz,4.8～5.0 GHz)frequency band,weighing the contradiction between miniaturization and high isolation,and conduct research.The main works of the thesis are as follows:(1)A 4×4 compact MIMO antenna for the Sub-6 GHz frequency band is designed which antenna elements are placed orthogonally.The antenna elements include a feeder on the front face of the dielectric substrate,a loop embedded in the feeder,and L-shaped and F-shaped radiating patches connected the feeder line.Four separate ground patches were dug out 90°scallops and L-shaped floor branches for good isolation and miniaturization.Finally,the simulation results show that the designed MIMO antenna operates in the range of 3.24～3.68GHz and 4.77～5.04 GHz,and the isolation is better than-16 d B.The antenna uses two methods:adding parasitic elements and floor stubs to reduce Sub-6 GHz dual-band coupling and enhance impedance matching.In the Sub-6 GHz band,the gain varies from 2.7 to 4.4 d Bi and ECC is less than 0.025.(2)A compact three-band MIMO antenna is designed with a simple structure and its size is still 38×38 mm~2.The"S"-shaped antenna unit is constructed using bending radiating branch technology to cover the Sub-6 GHz low frequency band.The terminal is connected to the rectangular patch for fine-tuning the frequency band.The short parasitic branch next to the rectangular patch and the dug out T-shaped slot are for further Fine-tune the frequency band.Abandoning the time-consuming and labor-intensive shortcomings of the multi-branch method,the same antenna unit is used to place diagonally symmetrically so that the four ports can radiate two frequency bands:antenna port 1 and port 3 cover the low frequency band 3.06～3.74 GHz and 4.08～4.28 GHz;port 2 And port 4 covers the high frequency band 4.80～5.02 GHz.The isolation is better than-16.2 d B by adding a long parasitic element unit on the front of the substrate and four pinwheel-shaped metal patches orthogonally combined with four inferior arc circles in the center of the floor to enhance the isolation.In the sub-6 GHz band,the gain is up to 4.5 d Bi and ECC is less than 0.05.(3)A 4×4 MIMO antenna based on EBG and CSRR is proposed whose units are placed orthogonally.The antenna unit includes a feeder located on the front of the dielectric substrate.The left side of the connecting feeder is an L-shaped radiating patch with seven circular patches,the right side is a stepped radiating patch,and the left L-shaped radiating patch on the side covers the desired low frequency band,and the stepped radiating patch on the right covers the high frequency band.To improve return loss,four L-shaped CSRR structures were dug out of the ground.The embedded five-via mushroom EBG structure is to enhance isolation further.Finally,it is measured that the antenna obtains isolation less than-17.5 d B and-19.5 d B under the operating bandwidths of 3.28～3.62 GHz and 4.78～5.04 GHz,respectively.In the sub-6GHz band,the gain is up to 4.5 d Bi and ECC is less than 0.035. |
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