| With the rapid development of fifth-generation mobile communications(5G),the limited resources of the sub-6 GHz(Sub-6 GHz)microwave band cannot meet the massive data growth,while the millimeter-wave band has attracted much attention because of its abundant spectrum resources that can provide wider bandwidth and can significantly increase the data transmission rate.As an important component of millimeter-wave communication systems,millimeter-wave antennas are often required to have wide operating bandwidth,low cross-polarization level,stable radiation performance,and compact structure.Among various types of millimeter-wave antennas,planar dipole antennas have an important research value due to their excellent performance.It is foreseen that the millimeter wave band will work in concert with the Sub-6 GHz band in the future5 G communication system to meet different operating scenarios.Therefore,the study of broadband microwave/mm-wave common aperture antenna arrays is also of great importance.The dissertation focuses on millimeter-wave planar dipole antennas,and the main research works are as follows.1)A balanced antipodal dipole antenna unit fed by SICL is proposed.A balanced antipodal dipole antenna with three dipole arms is proposed based on the substrate integrated coaxial line(SICL)feeding structure.The middle dipole of this antenna is directly connected to the inner conductor,and the other two dipoles are placed face to face,so that the vector sum of electric field components from the middle dipole arm to the top dipole arm and the bottom dipole arm is parallel to the dielectric substrate,and the electric field components in the vertical direction will be cancelled,so that the cross-polarization level can be greatly improved,making the cross-polarization level below-30 dB.Meanwhile,the dipole arm can be used in the form of a long dipole arm and etching gaps on the arm,the dipole antenna can add an operating mode and obtain more than 65% of the operating bandwidth without changing the other structures of the antenna.2)Two 1×8 wideband planar dipole antenna arrays are proposed.Firstly,in order to further increase the gain to meet the demand for high gain in millimeter wave communication system,a1×8 equal amplitude fed broadband dipole antenna array is proposed with simple structure of array feeding network and in-band insertion loss less than 0.8 dB.And then,Then,a 1×8 low sidelobe broadband planar dipole antenna array is proposed using Taylor synthesis method in order to reduce the sidelobe of the array and improve the immunity of the antenna to electromagnetic interference.The overall sidelobe level of this array is below-18 dB,and the simulated feeding network has expected amplitude distribution and small phase difference.Both antenna arrays have more than 50% of the operating bandwidth and the cross-polarization levels are below-20 dB.3)A wideband common-aperture dipole antenna array for Sub-6 GHz and millimeter-wave bands is proposed.A common aperture antenna scheme is proposed based on the dipole antenna study in Chapter 3,where a 1×4 millimeter-wave array is nested on a Sub-6 GHz dipole antenna.The Sub-6 GHz antenna also takes the form of a long dipole antenna with gaps so that the antennas in both bands have a wide operating bandwidth.The millimeter-wave antenna is independently fed by SICL,which can achieve the integration of the two antennas and keep their radiation independently without interfering with each other,thus improving the isolation between the two bands.The final test results are in general agreement with the simulation results,achieving wide impedance bandwidths of 50% and 73.1%,cross-polarization levels below-22 dB and-20 dB,and isolation better than 30 dB and 15 dB in the Sub-6 GHz and millimeter wave bands,respectively. |
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