Miniaturization And Key Technology Research Of 5G Base Station Antenna

The research on 5G base station antenna is becoming more and more popular with its development and promotion for the reason that the base station antenna in 5G communication system has greatly changed in function compared with 4G,especially the beam scanning,which is the most important function.There are two general ideas for the implementation of beam scanning of 5G base station antenna,one is to achieve the phase shift of the feed network by combining the large-scale antenna arrays;the other is to interchange the radio frequency（RF）switch with different feeds with the help of the converging effect of electromagnetic lens on electromagnetic beam.The key issues of 5G base station antenna research are roughly as the following based on these two ways of implementing beam scanning:1.The miniaturization of the base station antenna unit;2.Ensuring that the isolation degree between the ports in the array does not deteriorate while reducing the antenna array spacing;3.The manufacturing process of the electromagnetic lens;4.The structural design of the electromagnetic lens feed antenna.This thesis has designed and processed three physical objects based on the mentioned characteristics of 5G base station antenna:the first is a low-profile dual-polarized circular dielectric vertical column two-in-one patch antenna unit;the second is the decoupling radome used to improve the isolation degree of the antenna port array;the third is the millimeter wave dielectric lens antenna array based on 3D printing.The idea of making the first two physical objects achieve beam scanning is to combine large-scale antenna arrays,while the third is to employ the beam converging effect of the lens.Firstly,a low-profile dual-polarized circular dielectric patch antenna with a working frequency of 2.515-2.675GHz for Sub-6G has been designed and processed in response to the requirements of 5G for base station antenna miniaturization.The antenna part has been formed by pressing two layers of the same circular medium.There are circular metal patches on the top layer of the medium and a layer of metal in the middle of the antenna after pressing.This design makes a strong resonant electric field between the two layers of metal patch,thus obtaining higher gain.The feed network has been printed on a double-layer rectangular dielectric board,and the feeding has been achieved through±45°coupling line controlled by two ports to realize orthogonal dual polarization.The circular medium and the feed network are again bonded together by adhesive,making the overall structure simple and reliable.The final height of the antenna is only0.06λ₀（λ₀ is the wavelength at 2.6GHz）.The antenna has been physically processed and tested and the result shows that in the 2.515-2.675GHz band,the S11 parameter is less than-10dB,the isolation degree is about-30dB,and the actual gain measurement result is up to 9.8dB（at the 2.6GHz frequency point）,width of horizontal half power lobe is 80°±3°and the width of vertical half-power lobe is 33°±2°.Secondly,a decoupling radome for the antenna unit mentioned above has been designed in order to improve the isolation degree in the array.The main body of the radome is a layer of dielectric board with low dielectric constant and low loss,on which metal patch structure is periodically printed.By adjusting the shape of the metal patch and the distance between the radome and the antenna array,the reflected wave generated by the radome has the same amplitude and opposite phase as the coupling wave in the array,and the two cancel each other,thereby achieving the effect of increasing isolation degree.The above-designed units have been assembled into a binary antenna array to study the port isolation degree between adjacent units in the array.The radome and antenna array have been physically processed and jointly tested and the result shows that the isolation degree of the inner and outer elements is about-20dB and-22dB respectively before loading the decoupled radome;After the radome is loaded,the isolation degree of the inner unit is improved about 8dB between 2.5-2.61ghz,and the co polarization isolation degree between the units is significantly improved between 2.5-2.68ghz,besides 2.6GHz frequency point improved by 10dB.By comparing the radiation pattern characteristics of the antenna before and after loading the radome,it has been found that the radome can improve the port isolation degree under the premise that the radiation characteristics of the antenna unit are basically unchanged.Finally,a millimeter-wave dielectric lens antenna array based on 3D printing has been designed according to the manufacturing process of the electromagnetic lens and the structure of the feed antenna.3D printing technology used to make electromagnetic lens promises high accuracy and low cost.The working frequency of the lens antenna array is25.5-26.5GHz,and its structure is divided into two parts:the first part is a cylindrical dielectric lens based on 3D printing,with many regularly arranged air holes in a cylindrical medium,achieving a gradual change of dielectric constant from inside to outside;the second part is an arc-shaped feed antenna array and the antenna unit is patch antenna with the 4×8 arrangement.The antenna units are bonded to a metal circular arc-shaped structure,and the antenna unit is directly fed through 32 connectors.The structure of this feed antenna is highly matched with the cylindrical lens,and is easy to operate.The lens and antenna array have been physically processed and tested and the result shows that the lens has a convergence effect on the radiation pattern of the antenna unit,which increases the maximum gain by 9.8dB to 15dB,and the HPBW is about 15°±3°,which promises the beam scanning function can be realized within 120°of the horizontal plane and the spacing between adjacent beams is about 15°±3°.