| Multiple-Input Multiple-Output(MIMO)communication system has received much attention and research by scholars due to its large channel capacity and high transmission rates.As an indispensable part of the system,MIMO antennas play an important role in the present and future communication field.In the new era of 5G,the Massive MIMO technology,derived from MIMO technology,will also become one of the revolutionary technologies.However,while MIMO antennas have obvious advantages,they also have disadvantages.On the one hand,the electromagnetic coupling will reduce the channel capacity,throughput,and SNR(signal-to-noise ratio)on the system.On the other hand,it will reduce the efficiency and gain of the antenna,and change the radiation pattern on the element.Based on this research background and historical inevitability,three miniaturized MIMO antennas with good performance for the three decoupling directions of MIMO antennas are studied and designed respectively in this thesis.Firstly,the width of decoupling bands of MIMO antenna is studied.A two-port MIMO antenna with broadband decoupling is designed,with an antenna size of 26 mm ×38 mm × 1.6 mm,and working bandwidth of Ultra-Wide Band(UWB),in the frequency band 3.1-12 GHz.The isolation of the antenna is higher than 19 d B in the 3.4-12 GHz band,and the decoupling frequency band is generally wide.The antenna achieves its broadband decoupling goal by combining the T-shaped ground branches for decoupling in the low and medium frequency bands and a Complementary Split-Ring Resonator(CSRR)for decoupling at high frequencies.The antenna is finally fabricated on the FR4 dielectric substrate,and both the simulation and test results show that the proposed antenna performs well in the MIMO system.Secondly,the number of decoupling bands of MIMO antenna is studied.A dual-band decoupling two-port WLAN-MIMO antenna with dimensions of 60 mm × 50 mm × 1.6mm is designed,covering WLAN bands 2.4-2.484 GHz and 5.15-5.35 GHz,where the antenna isolation is over 20 d B.The antennas are dual band decoupling by diverting and resonating the currents in both bands through two orthogonal slots in the ground.The antenna is finally fabricated and measured,and the measured results verify the performance of the antenna is good.Lastly,the number of decoupling ports of MIMO antenna is studied.A four-port UWB-MIMO antenna with dual band-notched characteristics that relieve the coupling between multiple ports is designed.The antenna has dimentions of 44 mm × 44 mm × 0.8mm,an operating bandwidth of 2.9-11 GHz(excluding the notched-bands of 3.3-3.9 GHz and 5-6 GHz),a coupling between antenna ports of degree less than-15 d B in the UWB frequency band,and two notched frequency bands.The antenna realizes the decoupling and obtains the notched band of Wi MAX frequency band by adding inverted L-shaped double ground stubs,and the band rejection characteristic of WLAN frequency band is achieved by etching a C-shaped slot in the radiation patch.Finally,the antenna is tested and the results are in good agreement with the simulated data,proving that the proposed antenna has an excellent performance in the MIMO system. |
