| With the rapid development of communication technology,the Fifth Generation(5G)has been widely commercialized due to its characteristics of high speed,low latency,and multiple links.However,the commercialization of 5G will not lead to the traditional 2G/3G/4G network retiring in a short period of time,which will make the space resources of base stations extremely scarce,thus affecting the large-scale deployment process of 5G base stations.Therefore,the 5G antennas are expected to share the same reflector and antenna cover with traditional base station antennas,achieving multiband shared-aperture base station antennas.In multiband shared-aperture base station antennas,there is strong coupling between antennas in different bands,which leads to antenna performance degradation.The more bands covered,the more severe the antenna performance degradation.In order to solve the coupling problem under the same aperture and cover more bands,this dissertation successfully achieves a compact triple-band shared-aperture base station antenna array by introducing a wideband bandstop frequency selective surface(FSS)and electromagnetic transparent antenna.Compared to the current commercial 5G band,the traditional 2G/3G/4G band has lower band,lower propagation loss,wider coverage range,and low deployment cost.With the further development of communication technology,the traditional low band is bound to be refarmed to 5G to compensate for the shortcomings of the existing high band,and greatly improve the quality of the existing communication network through high and low frequency networking.However,high band base stations have been laid on a large scale in major urban areas.If traditional shared-ground multiband shared-aperture antennas are used,the existing high band base stations will be destroyed,which will bring great losses and installation costs.In addition,traditional multiband shared-aperture antennas lack scalability and cannot meet the diverse needs of base station users.In order to solve these problems,this dissertation introduces a modular multiband shared-aperture base station antenna with high and low band antennas that do not share the same ground by introducing FSS with high transmission characteristics.The shared-aperture base station antenna does not need to damage the original high band base station.It can directly place the low band electromagnetic transparent antenna module integrated with high transmission FSS on the high band base station for functional expansion,greatly reducing the difficulty and cost of high and low frequency networking.Meanwhile,the introduction of modular concepts can also provide more selectivity to meet diverse requirement.The major work and novelties of this dissertation are summarized as follows:1.A triple-band shared-aperture base station antenna topology based on wideband bandstop FSS and electromagnetic transparent antenna is proposed,and a compact triple-band shared-aperture base station antenna with broadband characteristics,high integration,and low profile is achieved.In this topology,the wideband bandstop FSS is placed below the middle and high band antennas and above the low band antenna.The wideband bandstop FSS is used to isolate the influence of low band antenna structure on middle and high band antenna,suppressing the coupling of low band antenna to middle and high band antenna.In addition,the introduction of bandpass FSS into the design of middle band antenna results in electromagnetic transparency characteristics to high band electromagnetic waves,achieving good decoupling effects for middle and high band antennas.Finally,thanks to the triple-band shared-aperture topology,the wideband bandstop FSS,middle-band antenna array,and high band antenna array have played a certain loading role on the low band antenna,greatly reducing the profile height and achieving an overall antenna size effect of"1+1+1<1".2.A modular dual-band shared-aperture antenna topology based on high transmission FSS has been proposed to address the functional expansion issues of high band base stations in 5G high and low frequency networking.In this topology,the low band antenna needs to have electromagnetic transparency characteristics and not share the same metal floor as the high band antenna.A high transmittance FSS is introduced between the high and low band antenna as the equivalent reflective surface of the low band antenna.This high transmittance FSS has extremely high transmission characteristics at high band and will not affect the normal operation of high band antennas.At the same time,it has good reflection characteristics at low band to ensure the normal operation of low band antennas.In addition,the high transmittance FSS needs to have a metal mesh structure to facilitate integration with low band antennas into a low band electromagnetic transparent module.To verify the feasibility of this topology,this dissertation first designs an FSS based tightly coupled dipole array(TCDA-FSS)with high transmission characteristics at high band(3.3-3.8 GHz)and good reflection characteristics at low band(1.7-2.7 GHz).The low band electromagnetic transparent module composed of the TCDA-FSS and the band transparent antenna has stable radiation performance.The maximum gain impact of this module on high band antenna array under the same aperture scanning within the 60° range is only 0.8 dB,and the average gain impact is only 0.3 dB.3.To meet the requirements of the modular dual-band shared-aperture base station antenna in narrow transition band scenarios,this dissertation first designs a low band electromagnetic transparent antenna that exhibits electromagnetic transparency characteristics at high band 1.71-2.17 GHz and operates at 1.42-1.53 GHz.Then,a multi-layer FSS with high selectivity and high transmission characteristics is proposed.The multi-layer FSS achieved high transmission characteristics at high band and good stopband characteristics at low band by inserting transmission zero and loading a wide-angle matching layer,and it has a transition bandwidth of only 11.1%.Finally,based on the low band electromagnetic transparent antenna and multi-layer FSS,a modular dual-band shared-aperture base station antenna with a narrow transition band is proposed.Both simulation and measurement results indicate that the low band electromagnetic transparent antenna module composed of multi-layer FSS and low band electromagnetic transparent antenna has good radiation performance,while not affecting the performance of the high band antenna array.4.To meet the requirements of the modular multiband shared-aperture base station antennas in multiple scenarios,this dissertation further explores the performance of TCDA-FSS and designs an FSS based on wideband tightly coupled antenna array(WTCDA-FSS)with good stopband characteristics in the 0.69-0.96 GHz(L band)and 1.42-2.17 GHz(LB band),as well as high transmission characteristics in the 2.5-2.69GHz(H band)and 3.3-3.8 GHz(C band).Then,the transmission and reflection characteristics of WTCDA-FSS are verified through actual base station antenna array environments.Simulation results showed that the proposed WTCDA-FSS can serve as an equivalent reflective surface for L band and LB band antennas,while hardly affecting the radiation performance of the H band and C band antenna. |
