| The antenna growing trends of forming array and miniaturization make the couplings between antenna elements increasingly worse,which sharply deteriorates the performances of MIMO system.Due to this,decoupling becomes a problem which must be solved when developing MIMO.Traditional decoupling methods has some imperfections like lack of good extendibility and incapability of decoupling non-adjacent antenna elements.And they all take decoupling measurements after forming array.So,it requires us to study a new decoupling method which does not exist imperfections of traditional methods and takes decoupling measurements before forming array.Moreover,in consideration of two present decoupling effects,narrow-band decoupling might have very deep decoupling depth,but its decoupling bandwidth is not wide enough,while wide-band decoupling could have relatively wide decoupling bandwidth,but its decoupling depth is usually not deep enough.Thus,to achieve both deep and wide decoupling effect,it requires us to think a technique to combine advantages and avoid disadvantages of them.Additionally,as the quantity of antenna array element increases rapidly,the research on two-dimensional planar array decoupling cannot be ignored.Therefore,planar array decoupling is also worth exploration.The main work of this paper are as follows:Firstly,this paper proposes a novel and flexible decoupling method which is based on construction of weak-field region(CWFR)factitiously.Specifically,we generate a weak-field region nearby one single antenna element by designing a kind of decoupling structure.The key is,the location of this weak-field region must be accurately located at where we plan to put the second antenna element.Only in this way,can pre-decoupling be achieved before the formation of 1×2 antenna array.And the realization of pre-decoupling means that,isolation enhancement can be obtained naturally without rematch and redesign during forming array.Measured isolation is improved by 6 ～ 21 d B in the frequency band from 3.6 to 3.95 GHz.At the same time,simulated results of E-field distributions farther away from the single antenna element show that CWFR can construct many weak-field regions at once.So,without any structural changes or dimension adjustments,the decoupling structure can be expanded to 1×8 linear array directly.Simulation and experiment have also exhibited the significant isolation enhancement between 6 pairs of non-adjacent elements.Secondly,reconfigurable decoupling,which is a new kind of reconfigurability,is proposed in this paper.Reconfigurable decoupling is making S21 shift dynamically while keeping S11 unchanged.To clearly demonstrate this idea,monopole patch antenna is taken as an example,and a kind of decoupling structure is designed for it to generate a preliminary static decoupling effect at first.Then,the ethyl acetate liquid is arranged above the designed decoupling structure.By changing the volume of ethyl acetate,the preliminary static decoupling effect can be reconfigured dynamically.Although these reconfigured decoupling states are independent of each other,after synthesizing them together,a deep and wide decoupling effect can be obtained equivalently in the end.Furthermore,benefited by the fluidity of liquid,this reconfigurable decoupling effect has wonderful continuity and flexibility.Measured results indicate that a continuous decoupling reconfigurability is achieved from 3.1 to4.1 GHz(27.8%)with isolation better than-18 d B.Thirdly,this paper designs a kind of double-side decoupling structure to enhance isolation of planar array antenna.The designed decoupling structure consists of one top-side T-shaped stub and two bottom-side branch-shaped stubs.By adopting this decoupling structure,measured isolation of 2× 2 planar array is improved by 6 ～ 23 d B in the frequency band from 3.6 to 3.9 GHz.Furthermore,this decoupling structure exhibits remarkable decoupling capability both between adjacent and non-adjacent antenna elements in 2×4 planar array. |
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