Research On Compact Microstrip Circularly Polarized MIMO Antennas

With the rapid development of wireless communication technology,the communication system has the characteristics of high integration and large capacity,so the antenna in the communication system tends to be multi-polarization,miniaturization and wideband.Circular polarized wave(CP)has been paid more and more attention because of its important advantages in avoiding polarization mismatch and expanding antenna bandwidth.The circularly polarized multiple input multiple output(MIMO)antenna system does not have the problem of polarization mismatch between transmitter antenna and receiver antenna,and has outstanding characteristics in expanding channel capacity,improving spectrum efficiency and reducing production cost,thus realizing high quality wireless communication system.The traditional microstrip circularly polarized antenna has narrow relative bandwidth and single frequency band because of its high quality.Moreover,most circularly polarized antennas can only radiate circularly polarized waves in a single spin direction,which cannot meet the requirement of polarization diversity in communication systems.Therefore,three different types of microstrip circularly polarized antennas are proposed and fabricated in this paper.The main research contents are as follows:1)A microstrip dual circularly polarized antenna with a semicircular groove ground structure composed of two rectangular strips on the same side is proposed,which solves the problem that most circularly polarized antennas radiate single circularly polarized wave and have narrow relative bandwidth.The antenna optimizes the antenna’s circularly polarized radiation performance by etching a semi-circular slot on a rectangular patch in the upper left corner.The working frequency band of antenna can be changed by adjusting the size and position of the semicircular slot.The simulation results show that the antenna and its mirror antenna can generate left circularly polarized wave and right circularly polarized wave in the same frequency band.The antenna resonates in the 2.86-4.09 GHz band,and the axial ratio bandwidth of the dual circular polarization reaches 9.42%.The proposed antenna has polarization diversity and good radiation performance.2)A compact wideband dual-frequency microstrip circularly polarized antenna is proposed,which is composed of an embedded circular patch on a radial surface and a noncentral L-shaped feed and a ground surface.The antenna solves the problems of narrow band width and single frequency band of microstrip circular polarization antenna.Impedance matching of the antenna can be improved by adjusting the size and center position of the two circular patches on the ground.The measured results of the antenna show that the impedance bandwidth of the antenna is 46.4%(1.82-2.92GHz)and 40.5%(3.15-4.75GHz),and the antenna generates right-rotation circularly polarized waves in the of Wi-Fi(2.4-2.48GHz)and Sub-6G N77(3.3-4.2GHz)band.The proposed antenna meets the requirements of multiband,wide band and miniaturization of wireless communication technology.3)A compact four-port dual-circularly polarized MIMO antenna with a new decoupled structure consisting of type I and type II patches intersecting vertically is proposed,which solves the problems of large size and high coupling degree of most MIMO antennas at present.The MIMO antenna can radiate left or right circularly polarized waves at different ports.The new decoupled structure is cross-connected and merged at the antenna’s ground,which enables the antenna to achieve a wide axial ratio bandwidth and high isolation performance(16d B).The decoupled structure connects the four units of MIMO antenna to form a common ground,which ensures the practical performance of the designed MIMO antenna.The measured results show that the impedance bandwidth of the antenna is 14.6%(3.28-3.80GHz),and the axial ratio bandwidth is 30.3%(2.85-3.87GHz).The simulation results are basically consistent with the measured results,and the error is small.The antenna correlation coefficient,direction diagram and other indicators meet the technical requirements.