Research On Key Techniques Of Millimeter-wave Antenna For 5G Communications

With the rapid development of the information society,the explosive data exchange from mobile devices requires a high data rate for mobile communications.Therefore,the fifth generation of mobile communications(5G)comes into being.Simultaneously,the millimeter-wave(mm-wave)band with extensive spectrum resources is favored by 5G communication.As the device for transmitting and receiving signals,the significance of the antenna for the communication system is self-evident,and its performance also affects the overall performance of the communication system.In order to meet the requirements of 5G mm-wave communication on the antenna layer,this thesis focuses on the key technique research of mm-wave antennas from two aspects:point-to-point communication and point-to-multipoint communication.Moreover,exploratory research on the improvement of 5G mm-wave communication capacity and quality is also carried out.The research contents are as follows:1.For the wideband applications in 5G point-to-point communications,a wideband mm-wave planar horn antenna with enhanced impedance bandwidth is proposed.The multi-layered structure of the planar horn is constructed by stacking the dielectric substrates.By employing the layered dielectric technique,the impedance bandwidth is greatly improved and a stable gain is obtained.Further,the array design with triangular lattice arrangement is realized by combining the microstrip-line coupling feed,then high gain and low sidelobe levels are obtained.The experiments show that the proposed antenna can cover the common 5G mm-wave band,and the relative impedance bandwidth is more than 58.5%(from 21.9 GHz to beyond 40 GHz).2.For in-band full-duplex applications in 5G point-to-point communications,a high-gain dual-linearly polarized antenna array with high isolation is proposed.This antenna is based on the leaky-wave antenna.A dual-polarized antenna array is constructed by the proposed leaky-wave unit cells which can suppress open stopband and are suitable for differential feed.To realize the high isolation and the fixed beam in the boresight direction,a differential feeding network with two orthogonal channels is further designed.Finally,a fixed beam in the boresight direction and the inter-port isolation of more than 51 d B(27.5 GHz-29.5 GHz)are realized.3.For time or frequency division duplex applications,a high-gain dual-circularly polarized(dual-CP)antenna array with a low profile is proposed.The antenna is also based on the leaky-wave antenna,and the same unit cells aforementioned are employed.To realize the fixed beam,the antenna employs a differential feed based on the center excitation.The novel coupler is further proposed to provide CP excitation,and a dual-sequentially rotated feeding network is used to realize the dual-CP radiation.The antenna achieves a peak gain of 27.2 d Bic with only a profile height of 0.15?₀.4.For the point-to-multipoint communications(multi-user communications),a multi-beam antenna consisting of a parallel-plate Luneburg lens and an SIW open-ended waveguide feed is proposed.The lens is composed of multi-layered annular dielectrics with different widths.By changing the widths of the dielectrics,the equivalent refractive indexes can be changed.To decrease the beam spacing,an SIW open-ended waveguide structure with a transition is proposed as the feed of the lens.Then,the antenna achieves 11 independent beams with a beam spacing of only 9°,which can cover the angular space from-45°to+45°.5.For the multi-user communications,a parallel-plate Luneburg lens multi-beam antenna with 9 independent beams and a beam spacing of 15°is also proposed,covering the angular space of-60°to+60°.The antenna is only composed of upper and lower metal components and a circular single-layered dielectric substrate.By changing the height of the parallel-plate waveguide,the volume ratio between air and dielectric is changed,then the equivalent refractive index can be controlled to realize the Luneburg lens.The integrated WR-28 standard rectangular waveguide is served as the feed.The measurements show that the inter-port isolations of the antenna are more than 18 d B.6.For the improvement of 5G mm-wave communication capacity and quality,a CP reconfigurable antenna with enhanced axial ratio(AR)bandwidth is proposed.By analyzing the mechanism of the traditional annular slot antenna,an AR bandwidth enhancement technique based on resistor loading is proposed,which can increase the AR bandwidth by about 30%.Further,the switchable polarization is realized by the diode switches.Two improvements are proposed in the radiating layer and the feeding layer for the degradation of the antenna performance due to the parasitic effect of the diode.Finally,the proposed design is verified in the microwave frequency band.