| In the 5G Sub-6 GHz base station system,multi-band hybrid networking is widely used in many mobile communication operators.Thus,it is necessary to integrate 4G/5G base station antenna elements of different systems and different frequency bands into one antenna array.However,in the densely arranged multi-band base station antenna array,the adjacent crossband antenna elements cause strong interference to each other,resulting in the deterioration of antenna port-to-port isolation and pattern distortion.In order to solve these two problems,a cross-band self-decoupling method based on filtering and electromagnetic-transparent antenna elements is proposed in this paper.By combining the filtering and electromagnetic-transparent properties in the antenna element design,the cross-band coupling and the scattering interference between cross-band antenna elements are suppressed,simultaneously solving the problems of deteriorating port-to-port isolation and pattern distortion at the same time.Without additional decoupling elements or decoupling circuits,the multi-band aperture-shared base station antenna array with small volume and high performance can be realized.In the 5G/B5 G millimeter-wave(mm-wave)communication system,the antenna is usually integrated with the RF front-end chip.However,the mm-wave front-end chip has adjacent spurious frequency bands that need to be suppressed,which brings great challenges to the design of high roll-off,low loss and miniaturized filter.Therefore,it is necessary to integrate the filter function into the design of mm-wave Ai P.In addition,due to the limitation from the packaging process to the antenna design freedom as well as the overall antenna profile,resulting in the limited bandwidth,which can not meet the requirements of mm-wave wideband and multi-band systems.To solve the above problems,this paper proposes a designing method of mm-wave wideband dual-polarized filtering antenna and another design method of mm-wave dual-band dual-polarized band-notched antenna.They achieve good filtering characteristics without additional filtering circuit,and achieves wideband performance with a compact antenna size.The specific research contents and main novelties of this paper are as follows:1.Aiming at the problem of deteriorated port-to-port isolation caused by the mutual coupling between cross-band base station antenna elements,this paper studies the isolation enhancement method based on filtering antenna.Due to the out-of-band radiation suppression characteristics of filtering antenna,the port-to-port coupling between cross-band filtering antennas can be reduced.Firstly,a filtering antenna design method based on non-radiative resonance mode is proposed in this paper.Multiple radiation nulls are introduced by manipulating the non-radiative resonance mode of the antenna structure,realizing the bandpass filtering response with of high roll-off rate,high suppression level and wide stopband.At the same time,due to no additional parasitic structure or filtering circuit is required,the in-band performance of the antenna is almost not affected,and the compact size and simple structure can be achieved.Based on the method,this paper presents two different dual-polarized filtering antenna designs which are employed in the 4G/5G multi-band base station arrays,realizing high cross-band port-to-port isolation.2.Aiming at the pattern distortion problem caused by the mutual blockage effect of crossband base station antennas,this paper studies the pattern recovery method based on electromagnetic-transparent antenna.Firstly,this paper proposes a design method of electromagnetic-transparent antenna based on composite metasurface structure.By constructing a composite periodic structure with wave-transmission property and designing it as an electromagnetic-transparent antenna radiator,which can effectively pass through the electromagnetic wave of specific frequency band,greatly reducing the blockage effect of the cross-band antennas.Also,the radiation patterns of the cross-band antennas are approximately intact when blocked by the electromagnetic-transparent antenna.Then,this paper presents different types of dual-band aperture-shared antenna array according to the frequency ratio between the high-band and the low-band.In the dual-band aperture-shared array with large frequency ratio,the array layout by inserting an electromagnetic-transparent low-band element into 4×4 high-band elements are adopted.In the dual-band aperture-shared array with small frequency ratio,the array layout is by nesting the electromagnetic-transparent low-band element with a single high-band element.Both of the dual-band aperture-shared arrays possess good radiation patterns and performances due to the radio-tranparent antenna.3.In order to simultaneously solve the two problems of port-to-port coupling and pattern distortion between cross-band base station antenna elements,this paper presents an antenna design integrating filtering and electromagnetic-transparen properties which is applied into the self-decoupled dual-band aperture-shared array design with one low-band element and four high-band elements.By combining the electromagnetic-transparent radiator and the filtering balun structure,a low-band antenna element with supressed upper-band and electromagnetictransparent characteristic is proposed in this paper.In addition,by adding parasitic elements on the high-band antenna element,the properties of lower-band suppression and in-band decoupling are realized.Based on the above low-band antenna element with electromagnetictransparent and filtering characteristics and high-band antenna element with filtering and inband decoupling characteristics,the self-decoupled dual-band aperture-shared array is achieved,with high cross-band and in-band isolation and good radiation patterns without additional filtering circuit or decoupling element,and maintains high performance in a compact array layout.4.Because it is difficult to integrate the filter with high roll off and low loss in the mmwave front-end chip,this paper proposes a mm-wave Ai P integrating the filtering characteristics,which significantly reduces the performance requirements of the front-end filter.By adjusting the non-radiative resonant mode of antenna radiator and parasitic elements,it can not only introduce radiation nulls and realize the filtering response with high roll-off rate,but also introduce additional resonant mode in the operating frequency band to widen the antenna bandwidth.Based on this method,a mm-wave wideband dual-polarized bandpass filtering antenna and another mm-wave dualband dual-polarized bandstop filtering antenna are proposed in this paper.In this paper,the design theories and methods of filtering antenna and electromagnetictransparent antenna as well as their aperture-shared antenna arrays have benn studied,to meet the urgent requirements of 5G/B5 G mobile communication for highly integrated,multi-band and multi-functional integrated antenna. |
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