Research On Improving The Isolation Of Antenna In MIMO System

The antenna is an indispensable part of the MIMO system,the performance of the antenna determines the quality of the system.As the system grows in the direction of miniaturization and integration,multiple antennas are placed in the space of limited size,resulting in a reduction in the spacing between the antenna elements,which inevitably results in low isolation and high correlation.The research of this paper mainly aims at improving the isolation of dual-band MIMO antenna,and decoupling by adding decoupling network to the feed port of the antenna.The design of the phase shift,decoupling and matching of the method is carried out in turn,the design idea is clear,the design of the antenna and the design of the decoupling network are carried out separately to make it have a certain universality.The main research work of this paper includes:Firstly of all,the decoupling network is added in parallel in the antenna unit,and the method of transforming the scattering matrix into admittance matrix is used to analyze the dual-band decoupling condition and matching condition expressed by admittance.In order to enhance the matching performance of the antenna,the matching network of the LC lumped element and the matching network of the step impedance are analyzed.Secondly,the decoupling characteristic of the neutralization line is obtained according to the decoupling condition of the coupled antenna.The influence of the step impedance line and the uniform impedance line as the phase shift network on the antenna matching performance is analyzed and discussed.The LC lumped element matching networks in the enhanced antenna impedance matching with different ttopologies are also analyzed and discussed.After simulating and processing of physical,the antenna isolation is improved by more than 15 dB at low frequencies and9 dB at high frequencies.Thirdy,according to the coupled resonant method,the admittance matrix composed of coupling parameters is obtained.Based on the double-frequency decoupling condition and matching condition,a double resonator composed of an open resonant ring is designed as a decoupling network based on the step impedance line.The matching network composed of the step impedance line compensates the damage of the phase shift network to the original matching of the antenna and enhances its matching performance.Finally,the double resonator is replaced by the ring resonator as the decoupling network.The odd-even model method is used to obtain the admittance parameter of the ring resonator,which satisfies the decoupling condition to obtain the initial value of the ring resonator.The antenna unit with high isolation is obtained by the method of optimization.Antenna isolation with two different decoupling networks is increased to more than 20 dB at both low frequency and high frequency.