| In the age of fifth-generation(5G)communication,wireless communication technology has leaped forward,and people urgently need higher channel capacity and faster transmission speed.Compact MIMO array based on multi-input multi-output(MIMO)technology can maximize channel capacity in a limited space.However,there are many kinds of extremely high coupling in the closely arranged MIMO array,which reduces the channel capacity.Therefore,MIMO array decoupling has become the focus of many scholars.In addition,an overly complex decoupling scheme will not only increase the size of the MIMO array or affect the radiation performance,but also increase the complexity of the array and reduce the design efficiency.Therefore,how to concisely realize compact MIMO decoupling array has become an urgent and challenging problem.To solve this problem,based on modes cancellation decoupling theory,the decoupling schemes of MIMO arrays with different types of coupling and tight arrangement is studied in this dissertation.The work of this dissertation is mainly summarized as follows:1.The modes cancellation decoupling theory is proposed,which is the fusion of odd and even modes decoupling theory and eigenmode theory.The modes cancellation decoupling theory extends odd and even modes to various eigenmodes,and the mutual coupling degree is judged by the impedance.For the multiple types of mutual coupling of MIMO array,two compact antenna elements are considered as a whole structure,and the mutual coupling is defined by eigenmode from the perspective of internal field.In this way,the multiple coupling is changed into multiple eigenmodes of the antenna,and the multiple array decoupling problem is changed into the impedance problem of adjusting different eigenmodes.In addition,the eigenmode theory can also guide the design process of decoupling array.2.For the collinear coupling of MIMO array,TM02/03 modes cancellation decoupling theory is proposed.TM02 and TM03 modes are adjusted through adding some electromagnetic perturbation structures and three arrays with high isolation are designed.For the first array,TM02 mode is adjusted through adding shorting pins and TM03 mode is adjusted through etching slots on the antenna.The two-element decoupling array is designed when the resonance frequency and impedance of TM02 mode are consistent with that of TM03 mode,respectively.Under the condition that the edge-to-edge spacing is only 0.34λ0,the in-band port coupling of the first array is reduced to less than-30 dB,with a minimum of-65 dB,while maintaining a stable radiation pattern.In addition,the channel capacity of the array antenna is increased by 20%through decoupling,and then two-element array is extended to the eight-element decoupling array.On the basis of adjusting TM03 mode by etching the slot on the antenna,the decoupling is realized by loading the substrate integrated waveguide slot which can only be excited by the TM02 mode.Compared with traditional defected ground slot(DGS),waveguide slot antenna can also reduce the backward radiation.In order to prove that the proposed modes cancellation decoupling theory can be combined with existing decoupling schemes,ADS is introduced into the first array antenna to reduce parallel coupling,and the decoupling principle of ADS is explained through impedance analysis.Finally,a dual-polarized four-port two-element decoupling array is obtained.3.For the parallel coupling of MIMO array,four arrays with high isolation are proposed based on multiple modes cancellation.First,TM10/11 modes cancellation is realized when TM11 mode is adjusted through etching slots on the ground,and the mutual coupling of the first array is reduced to below-20 dB.In addition,the surface current distribution and impedance of TM02 mode is changed by adding a shorting pin,and TM11/02 modes cancellation is realized.In this case,the in-band mutual coupling of the second array is reduced to below-27 dB,with a minimum of-72 dB.Next,TM10/11 mode cancellation,TM11/02 mode cancellation and TM02/03 mode cancellation are fused to form TM10/11/02/03 multi-modes cancellation decoupling theory.The surface current distribution of TM02 mode and TM03 mode is planned by adding a shorting pin and etching slot on the antenna,and the broadband decoupling array is obtained.The mutual coupling of the third array is less than-20 dB within 36.6%of the relative bandwidth and the mutual coupling is lower than-24 dB within 28.6%of the relative bandwidth.In addition,the TM20 mode is used as the working mode of the fourth array.On the basis of miniaturization design,the odd mode impedance is reduced by loading PIFA to achieve modes cancellation decoupling,and the port coupling is reduced to below-29 dB.4.The modes cancellation decoupling theory is applied to multiple polarization MIMO array,and three multiple polarization arrays with high isolation are proposed.TM03/04 modes cancellation decoupling theory is proposed.TM03 and TM04 modes are adjusted through adding T-type branch and etching slots on the antenna,and the two-element decoupling array with mutual coupling below-23 dB is obtained.After deforming and rotating the twoelement decoupling array,a dual-polarized four-port decoupling array with port coupling less than-27 dB is obtained.In the design process of the first decoupling array,the parasitic effect of cross-polarized elements is fully considered,which is expressed as the change of impedance.The reverse surface current of the cross-polarized elements is also fully considered,and the pattern of the first decoupling array antenna is improved by etching slots.In addition,a massive dual-polarized decoupling array is realized by introducing parasitic elements.In the design process of the second decoupling array,the element of the dualpolarized four-port decoupling array is regarded as a polarization translator and expanded into a meta-surface element to reduce the in-band RCS.At the same time,the parasitic effect of the cross-polarized element is used to reduce the coupling.Finally,a meta-surface antenna array with an in-band RCS reduction of more than 10 dB and a minimum port coupling of-35 dB is obtained.For the three-element rotationally symmetric array,the third element is regarded as the parasitic structure of the other two elements.The three-port mutual decoupling array antenna is realized by changing the shape and size of the element and loading the shorting pins.In addition,the radiation pattern of the array antenna is improved by etching the slots on the antenna.Finally,the three-port mutual decoupling array antenna is extended to a massive multi-port decoupling array antenna by using the rotational symmetry again.5.The application of new materials in array decoupling is explored.Firstly,a waveguide metamaterial with dual-frequency blocking characteristics is proposed to realize dualfrequency decoupling array.In addition,the composite magnetic material is placed under the antenna to reduce the odd and even mode impedance difference and frequency difference of the array antenna.The influence of various parameters of the composite magnetic material on the antenna is analyzed.Finally,a high isolation array antenna based on the magnetic material is designed and fabricated.The port coupling of the array antenna is lower than-29 dB,and the minimum coupling can reach-55 dB. |
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