| The large-scale multiple-input multiple-output technology meets the requirements of communication systems for high channel capacity and ensures the reliability of data transmission.Due to the limitation of system space and the dramatic increase of elements,the mutual coupling effect between antennas becomes significantly obvious,which seriously deteriorates the matching and radiation characteristics of antennas and increases the nonlinearity of power amplifiers,degrading the communication quality of communication systems.Therefore,it is significant to suppress the mutual coupling of antenna array to improve the performance of communication system.In this thesis,decoupling methods and structures are proposed for antenna arrays with different polarizations and scale,and the decoupling effect on power amplifiers in transmitter arrays are explored,with the following main designs and contributions:1)To enhance the isolation in a compact large-scale base station array,a hybrid decoupling structure consisting of a dielectric board,metal baffle,and feeding network is proposed.The neutralization dielectric board based on neutralization-schemes provides a new signal path to cancel the original mutual coupling,and the metal baffle based on partition-schemes is employed to suppress the propagation of the space electromagnetic wave.The antenna elements in the vertical direction are excited by a feeding network.A 4×4 base station array with a horizontal edge-to-edge distance of 0.38 free-space wavelength,with relative bandwidth of 25%,is designed and fabricated.Simulated and measured results show that the the voltage standing wave ratio is less than 1.7,and the isolation between any two ports in the array is better than 20 d B within the entire operating frequency band.Stable radiation patterns with a good front-to-back ratio and cross-polarization ratio are achieved.2)A parasitic decoupling structure with polarization rotation property(DSPR)is proposed to reduce the mutual coupling between co-or cross-polarized antennas.The proposed DSPR generates neutralization waves with two orthogonally polarized components that can be controlled to cancel the original mutual coupling.In order to verify the decoupling capability of the designed results,two arrays with orthogonal and parallel dipole elements are designed.After applying the DSPR,the mutual coupling at the center frequency of 3.5 GHz is reduced to-40 d B for both arrays,and the overall mutual coupling is better than-26 d B within the band of 3.3-3.7 GHz,and the reflection coefficients remain below-12 d B.The antennas maintain stable radiation patterns within the operation bandwidth with a 0.5-d B increase of the realized gain.The decoupling effect of the proposed structure on circularly polarized waves is verified by designing a circularly polarized antenna excited by an ideal network and a power-division phase-shift network,respectively,the mutual coupling between circularly polarized antennas in a 1×4 array is reduced to below-35 d B thanks to the DSPR,and the axial ratio is significantly improved by less than 2 d B.Finally,the measured results match with simulated ones,proving the decoupling effectiveness of the proposed structure.3)Based on the decoupling research on large-scale base station array,the decoupling effect on the transmitter array’s nonlinearity is experimentally investigated using power amplifiers to excite the base station array prototype.The mutual coupling of the array can be effectively suppressed using a decoupling structure.Two continuous-wave(CW)signals at different frequencies are injected into the PAs,and the output signal of each PA is measured via a coupler.The measured results show that with effective mutual coupling reduction,the PA interference is greatly suppressed by up to 16 d B,and the power of the useful signal is enhanced by up to10 d B. |
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