| In the development process of wireless communication,the user experience is continuously optimized.With the increasing demand for better communication quality among the people and various industries,the 5th generation of wireless systems(5G)has been gradually promoted.Among them,the use of millimeter-wave technology will alleviate the shortage of spectrum resources,greatly increase the data transmission rate and achieve low-latency communications at the same time.As an important part of wireless communication,millimeter wave antennas have attracted extremely high attention to researchers.However,many issues in promoting millimeter-wave applications should be noticed such as high loss,fast attenuation,limit propagation distance and narrow coverage.To address the above issues,this thesis focuses on the research of high-gain millimeter-wave multi-beam antennas operating in 24 GHz.Specifically,two dual-polarized millimeter wave multi-beam antenna arrays based on the improvedButler matrices are proposed,which achieved a wide-angle scanning with low sidelobe level.And a millimeter-wave multi-beam transmit array is proposed to realize a wide coverage and low gain tolerance,whose compensation phase distribution varies with the area.The main contributions of this thesis are listed as follows:1.Completed the research of dual-polarized multi-beam antenna array based on the conventional Butler matrix.Firstly,an analysis is made for the working principle of the 4×4Butler matrix,and a complete matrix is designed.Secondly,a dual-polarized antenna array is designed and optimised using a hybrid feed network.Finally,connecting the conventional Butler matrix with the dual-polarized antenna to form a multi-beam radiation,simulation result shows the antenna gain reaches to 17.1dBi.2.A dual-polarized multi-beam antenna array based on an improvedButler matrix is proposed.Two improvedButler matrices with unequal current distributions are designed and optimised for the problem of high sidelobe level caused by conventional Butler matrix feed networks,which effectively suppress the sidelobe level when the multi-beam antenna array makes wide-angle scanning.In particular,design I achieves a tapered power output from a4 x 4 Butler matrix by loading power dividers at the Butler matrix terminals,resulting in a sidelobe level maintained below-10 dB over the multi-beam pointing range and a maximum gain of 15.7 dBi.Compared to the conventional Butler matrix,the modified 4×4 Butler matrix achieves a 3dB drop in the sidelobe level at the maximum sweep angle.Based on this,Design II proposed a 4 x 6 Butler matrix to achieve a multi-beam antenna array with the maximum gain of 18 dBi.Meanwhile,the sidelobe level is maintained below-14 dB.3.A metasurface-based multi-beam antenna array with different compensation phases is proposed.A method of designing metasurface transmitarray based on partitioned hybrid phase distribution is proposed to address the problems of narrow scanning range and low gain tolerance of matasurface-based transmitarray.The method effectively widens the beam scanning range of the metasurface transmitarray and reduces the gain loss caused by beam scanning.Based on the above method,a multi-beam transmitarray antenna is proposed and simulation result shows the antenna reaches the scanning range of ±28°,a maximum gain of20.2 dBi and a gain tolerance of 0.8 dB.The measured result shows that the scanning range of the antenna is 56°,with the maximum gain of 19.9 dBi,and the gain tolarance of 1 dB. |
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