Tri-Band Aperture-Shared Antennas For Sub-6GHz Base Station Applications

The mobile communication in China faces the situation of multi-band,multi-standard,and multi-system coexistence.Due to the difficulty of site selection of base stations and limited installation space,base station antennas tend to develop in the direction of multi-frequency,miniaturization and lightweight.By combing multiple antennas working in different frequency bands on a shared aperture,a multi-band aperture-shared antenna can be formed,which is a desirable solution for the current and future base station antennas.Therefore,a comprehensive investigation has been carried out on the operating mechanism and implementation methods of the tri-band aperture-shared antennas and arrays in this thesis.The selected operation bands are 0.69-0.96 GHz for the low band,1.7-2.2 GHz for the middle band,and 4.8-5 GHz for the high band for 2G/3G/4G/5G applications.The specific contents are as follows:A fully aperture-shared tri-band antenna is proposed in this thesis,which is formed by placing a low-band(LB)antenna,a middle-band(MB)antenna,and a high-band(HB)antenna collinearly from top to bottom.Complex mutual coupling has arisen after the three antennas are aperture shared.Although there is no influence on the LB antenna,the MB antenna receives radiation shielding from the LB antenna,and the HB antenna encounters severe shielding effect from both the LB antenna and the MB antenna.This research proposes a decoupling technology based on choke and partially reflecting surface(PRS)to deal with the mutual coupling.A choke has been mounted on the LB antenna to suppress the induced MB current on the LB antenna,so that the performance of the MB antenna can be improved.After a PRS has been introduced above the HB antenna,a Fabry-Perot cavity is created between the PRS and the reflector to provide constructive interference for the HB radiation,so that the shielding effect on the HB antenna can be significantly alleviated.Meanwhile,the choke and PRS have little effect on the LBA.Experiment results show the fully aperture-shared tri-band antenna achieves good impedance matching and radiation performances over its three operation bands.A tri-band aperture-shared antenna of a LB antenna,a MB antenna and a HB array has been investigated.The tri-band aperture-shared antenna is developed from the fully aperture-shared tri-band antenna by extending the HB antenna to be a 2*2 HB array.The mutual coupling has the same effect on the LB and MB antennas with those for the fully aperture-shared tri-band antenna.There is double partial shielding effect on the HB array due to the new relative position between each element of the HB array with other antennas,leading to asymmetrical and distorted radiation patterns in the high band.The shielding effect on the MB antenna is still solved by using a choke.Two layers of PRS have been applied for dealing with the double partial shielding effect on the HB array.The choke and two PRSs have slight influence on the LBA.Simulation and experimental results illustrate that the tri-band aperture-shared antenna has good impedance matching,symmetrical radiation pattern and stable antenna gain over the three operation bands.A tri-band aperture-shared antenna array has been proposed and its subarray has been studied.The tri-band aperture-shared subarray is composed of a LB antenna,two MB arrays and four HB arrays,which are arranged with their center points collinearly placed from top to bottom.The mutual coupling is even more complex: there is an interference on the LB antenna from the induced common-mode current on the MB array;the MB array receives partial radiation shielding from the LB antenna;the HB array faces the double shielding effect from both the MB array and the LB antenna.Two kinds of different chokes have been applied on the LB antenna to solve the partial shielding effect on the MB array.Two newly designed PRSs have been introduced above the HB array to alleviate the double shielding effect on the HB array.Besides,ferrite cores are mounted on the feeding coaxial cables of the MB array to be used to suppress the induced common-mode current.It is shown that the tri-band aperture-shared subarray can be used to provide support for the three operation bands with good impedance and radiation performances.The investigation on the three tri-band aperture-shared antenna and array demonstrated that the decoupling technology based on choke and PRSs can effectively solve the mutual coupling of multi-band aperture-shared antennas,which provide a preferable technical solution for the implementation of mobile communication base station antennas.