Research On The Key Technologies Of Planar Antennas For Millimeter Wave MIMO Systems

5G communication technology is developing to millimeter wave band,and the research of millimeter wave antenna and MIMO array has become one of the current hot spots.The wireless communication system puts forward higher requirements for the antenna,such as high gain,miniaturization,convenient processing,good radiation characteristics and so on,which are the specific characteristics of the antennas with good performances.Planar antenna is widely used in 5G millimeter wave communication system because of its low profile geometry,easy manufacturing and integration with other equipment.In this paper,the TSA antenna array,cylindrical Luneburg lens antenna and 28/38 GHz dual-band antenna in millimeter wave MIMO system are studied deeply and some research results are obtained.The main contents and innovations of this paper are summarized as follows:(1)A compact TSA array antenna is proposed.By using the loading design of the gradual length comb slits of the TSA element,the length of the current on the surface of the TSA is extended,the width of the TSA is reduced,and the impedance characteristics of the TSA element are optimized.In addition,with reasonable design of comb size,mutual superposition of surface currents on the comb slits of TSA is obtained,thus a more flat phase distribution on the antenna interface is generated,which can improve the far-field radiation characteristics of the antenna.By using the compact SIW power divider and the structure characteristics of TSA antenna with slits,the dimension of TSA array antenna is effectively reduced while two adjacent TSA elements'radiation fins are in inverted design.The S₁₁<-10d B bandwidth of the antenna is 38.2-46.2 GHz.Compared with the traditional TSA array antenna fed by the one eighth power divider,the dimension of the proposed antenna is reduced by about 71%.The research results have been published in the international conference 2017 IEEE International Symposium on Antennas and Propagation&USNC/URSI National Radio Science Meeting(APS&URSI)and international conference of IEEE 7th Asia-Pacific Conference on Antennas and Propagation(APCAP)Conference.(2)A method of adjusting the phase of SIW transmission line by using the second-order inductive window is proposed,and a TSA array antenna based on the second-order inductive window is designed.Based on the equivalent circuit model of the second-order inductive window and the analysis method of the Two-ports network,a method of adjusting the output phase of SIW transmission line by using the second-order inductive window is proposed for the first time.The output phase of the compact SIW 1/8 power divider can be adjusted by loading the second-order inductive window.Combined with the theory of array antenna,the second-order inductive window can optimize the gain and side lobe level of compact TSA array antenna at the side frequencies.The S₁₁<-10d B bandwidth of of TSA array antenna loaded with the second-order inductive window is 38.9-44.5 GHz.In the target frequency band of 40.5-43.5 GHz,the gain of the array antenna loaded with the inductive window is higher than 13.4 d Bi,and the sidelobe level is 3.2-8.6 d B lower than that of the antenna loaded without the inductive window,while the dimension of the antenna is only increased by4mm.The research results have been published in the international core journal of IEEE Transactions on Antennas and Propagation.(3)A method of loading metal mesh with cylindrical Luneburg lens is proposed,and three kinds of cylindrical Luneburg lens antennas converging on E-plane are designed with this method.For the cylindrical Luneburg lens antenna converging on the E-plane,the E-plane electromagnetic wave converges through the refraction of multi-layer medium.But for the H-plane,the traditional parallel metal plate is no longer applicable.This paper presents a method of loading metal mesh on both sides of the cylinder to change the phase distribution of H-plane magnetic field,so as to reduce the side lobe level of H-plane,reduce the beam width of H-plane and improve the antenna gain.In addition,the method of loading metal mesh is verified by machining method and 3D printing method of Luneburg lens antenna.Taking the machined antenna as an example,in the H-plane of the antenna,the HPBW of the loaded antenna is 34.2°at 26 GHz,which is 12.3°narrower than that of the unloaded antenna.The side lobe level of the H-plane is-15.1 d B,which is 7.6 d B lower than that of the unloaded antenna.The research results of this part have been published in the international core journal of IEEE Transactions on Antennas and Propagation,International Journal of RF and Microwave Computer-Aided Engineering and international conference of IEEE 2019 11th International Conference on Microwave and Millimeter Wave Technology(ICMMT).(4)A novel 28/38 GHz dual-band patch antenna is proposed.Through the coupling gap of SIW transmission line,a pair of metal arms printed on the upper dielectric plate is fed.Two metal arms are respectively loaded with paired shorting pins.The paired-arms antenna works at 38 GHz and the current direction on the upper surface of the two arms is the same,which is superposed in the far field to form radiation.The antenna at 28 GHz adopts the microstrip patch antenna loaded with paired-shorting pins,which is introduced to realize inductive loading effect of antenna.The 28-GHz microstrip antenna and 38-GHz metal arm antenna are combined for the dual-band antenna.Since the surface current area of the antenna is totally different when it works at two frequencies,the correlation between the two working frequencies of the dual frequency antenna is very small.This realizes the independent adjustment of the two working frequencies of the antenna,and the antenna is suitable for the application of different frequencies of 5G millimeter wave MIMO communication scenarios.The two separated S₁₁<10 d B bandwidths of the antenna are 27.7-28.7 GHz and 36.8-40.2GHz,which means the relative bandwidth is 3.8%and 9.0%.Moreover,the gain of the antenna is 8.4 d Bi at 28 GHz and 6.1 d Bi at 38 GHz.This part of research results have been submitted to the international conference 2020 IEEE International Symposium on Antennas and Propagation&USNC/URSI National Radio Science Meeting(APS&URSI)and published in the international core journal of IEEE access.