| Multi antenna system is an important trend of mobile communication base station system,including traditional passive base station array antenna,traditional active array antenna and MIMO array under the development trend.However,with the increasing scale of array antenna,the coupling between elements is becoming more and more serious.The coupling problem between antenna elements of the same frequency in base station multi antenna system has become an important topic.With the development of base station antenna towards broadband,the decoupling problem of broadband base station array antenna also needs to be solved urgently.This paper is based on this background.Broadband base station array antenna requires broadband decoupling structure,but this is still a difficulty in academic research.The reason is that when the working frequency of the antenna unit changes,the coupling wavelength and coupling energy between the units will also change.The decoupling structure needs to offset or filter the coupling energy of different sizes in a wide frequency band.However,the decoupling structure is usually designed for the central frequency point and is difficult to be used in a wide frequency band.Taking the typical broadband dual polarization dipole unit as an example,this paper proposes three broadband decoupling structures to realize the decoupling of broadband base station array antenna.The proposed structure can not only improve the isolation and maintain stable and good radiation performance,but also realize broadband impedance matching.The main research results of this paper are summarized as follows:Firstly,a decoupling structure based on the principle of broadband band stop filtering is proposed.Based on the mechanism of stop band generated by resonator resonance,taking SRR as an example,cascading resonators is equivalent to cascading two band stop filters,which can effectively expand the stop band used to realize decoupling and realize broadband decoupling.Taking the typical 2 * 2 broadband dual polarization base station array antenna with working frequency band of 1.71-2.69 GHz as an example,the design process of cascaded SRR structure is introduced in detail,and the performance of single SRR and cascaded SRR in broadband decoupling is compared.Finally,the performances of the array before and after decoupling are compared.The results show that the decoupling structure not only improves the broadband impedance matching performance,but also reduces the co-polarization isolation to less than-22 d B,the cross-polarization isolation to less than-20 d B,the half power lobe width(HPBW)is stable in the good range of 65°±8°.So the decoupling effect is good.Secondly,a broadband decoupling structure based on notched director and periodic baffle is proposed.The director can be used to improve the radiation performance of the array,which itself is not suitable for the broadband array,but the proposed notched director is designed for the problem frequency band,and the radiation performance of the broadband array is improved by increasing the notch to avoid the interference of the director to other frequency bands.The periodic structure baffle is used to further improve the decoupling effect.Taking the typical 2 *2 broadband dual polarization base station array antenna with working frequency band of 1.71-2.69 GHz as an example(the structure is consistent with the first scheme),the design process of notched director and periodic structure baffle is introduced.Finally,the performances of the array before and after decoupling are compared.The results show that the decoupling structure not only improves the broadband impedance matching performance,but also reduces the copolarization isolation to less than-21 d B,the cross-polarization isolation to less than-25 d B,the half power lobe width is stable in the range of 65°±8° and the gain is increased by more than3.5d Bi.So the decoupling effect is good.Thirdly,aiming at the practical engineering background of "array coupling problem under the condition of small-size reflector",a broadband decoupling structure is proposed.The reduction of the horizontal size of the array brings space to the construction of the base station,but it increases the difficulty of array decoupling.In order to solve the array coupling problem under the condition of small-size reflector,firstly,the influence of reflector on the array is analyzed,and then three structural fusion schemes of antenna unit miniaturization,ceramic medium and baffle are proposed.The antenna unit miniaturization includes two steps: radiation arm folding and adding parasitic square ring.The negative impact of small-size reflector is solved by the combination of antenna unit miniaturization and ceramic medium,and the inherent coupling problem of broadband array can also be solved by the three schemes proposed.Taking the typical frequency band of 0.69-0.96 GHz as an example,the design process of decoupling structure is given.Finally,the performances of the array before and after decoupling are compared.The results show that the decoupling structure not only improves the broadband impedance matching performance,but also reduces the co-polarization isolation below-23 d B,which is improved by about 8.5d B.The half power lobe width is compressed to a good range of 69°-79° and the gain is also slightly improved.So the decoupling effect is good. |
