| In recent years,wireless communication technology has shown explosive growth.MIMO(Multiple-Input Multiple-Output)technology can build massive parallel data streams between the transceiver systems through spatial diversity and multiplexing.Under the condition of finite spectrum resources,the communication efficiency and reliability of the system are improved exponentially by MIMO technology,so MIMO technology stands out in the fifth generation mobile communication technology(5G).As an important carrier of MIMO technology,MIMO antenna plays a vital role.The coupling problem between antennas is a key problem faced by MIMO antenna technology.And for handheld mobile terminal devices,it is extremely challenging to place multiple antennas in an extremely narrow space and maintain a low degree of coupling between the antennas.The multi-port antenna has the characteristics of an array,which can further reduce the size of the MIMO antennas and improve the performance of the MIMO system.This paper mainly studies the working principle and design method of multi-port antenna,the formation mechanism and suppression method of mutual coupling between ports.The specific work content and innovation points of this paper are as follows:1.A high-isolation dual-port antenna with self-decoupling characteristics is designed for5 G mobile terminals.The antenna structure is that two ports simultaneously asymmetrically excite the F-type radiating patch.An equivalent transmission line theoretical model is proposed to explore the working principle of the dual-port antenna.The analysis results show that when the two ports of the antenna satisfy a specific layout,high isolation can be achieved without adding any decoupling structures.The-6 d B impedance bandwidth of the dual-port antenna is 3.4-3.6 GHz,the isolation between the two ports is greater than 16 d B,and the Envelope Correlation Coefficient(ECC)is less than 0.042.A set of 8 × 8 MIMO antenna arrays are designed and fabricated by placing four dual-port antennas mirror-symmetrically on both sides of the mobile phone substrate.The measured isolation and ECC of the designed 8 × 8 MIMO antenna array among the 8ports are greater than 15 d B and less than 0.2,respectively.The measured total efficiency is greater than 38.75 %,and the calculated channel capacity is 38.4-39.1 bps/Hz.2.A dual-port dual-loop antenna with zero clearance and high isolation is designed for 5G mobile terminals.The dual-port dual-loop antenna has a wider bandwidth than the dualport antenna in the previous section,and there is no clearance between the metal ground and the phone frame,which can still ensure wideband radiation performance.The reflection coefficient of the dual-port dual-loop antenna is less than-6 d B in the 3.3-3.92 GHz band,the isolation is greater than 15 d B,and the ECC is less than 0.15.An 8 × 8MIMO antenna array is designed based on four dual-port dual-loop antennas.The simulation results show that the isolation and ECC between the eight ports are greater than10 d B and less than 0.15,respectively.The radiation efficiency is greater than 65%.3.A tri-port antenna with shared radiator and self-isolation characteristics is designed for5 G mobile terminals.Compared with the dual-port antenna in the previous section,the triport antenna accommodates more ports in the same size,further realizing the miniaturization of the MIMO antenna.The antenna structure is that three ports simultaneously excite the "I"-like radiator printed on the inner surface of the frame of the mobile phone.The self-isolation characteristics of the antenna are analyzed by the mode cancellation method and the active reflection coefficient method.The isolation between ports of the tri-port antenna in the 3.4-3.6 GHz band is greater than 10 d B and the ECCs are less than 0.14.A 12 × 12 MIMO antenna array is designed and fabricatied by arranging four tri-port antennas symmetrically on both sides of the phone frame.The measured isolation and ECCs between the 12 ports are greater than 10 dB and less than 0.14,respectively,the measured total efficiency is greater than 51 %,and the calculated channel capacity is as high as 57.98-59.87 bps/Hz. |
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