Design And Research On Decoupling Technology For Circularly Polarized Antenna Array

The circularly polarized antenna has the advantages of receive arbitrary linearly polarized wave and reduce the interference of reflected signals.Large-scale Multiple-Input-Multiple-Output(MIMO)antenna system can expand the channel capacity.Due to the compression of the space for multiple antennas,serious electromagnetic coupling will exist,which ultimately deteriorates the performance of the antenna.How to improve isolation is an urgent problem that needs to be addressed in multi-antennas applications.In the past,most of researches focused on the decoupling between multiple linearly polarized antennas,while less exploration has been done for circularly polarized antennas.Impedance matching,coupling level and circularly polarized radiation characteristic should be considered in decoupling for circularly polarized antennas.Several decoupling methods for planar microstrip circularly polarized antennas are designed and studied in the paper.The aspects of work in the paper are arranged as follows:At first,the band stop decoupling structure is proposed for circularly polarized MIMO antennas with different intervals.The band stop decoupling structure can produce attenuate response to alternating coupling wave.The designed coplanar structure is embedded in the middle of antennas with large interval to hinder the propagation of surface waves,which the mutual coupling coefficient is reduced to below-50 dB.And the designed wall structure is placed between antenns with small interval to suppress the spatial waves with the coupling level below-25 dB.Both can achieve in maintaining circular polarization characteristic and low coupling level in impedance matching band.The wall structure can also be applied to the stacked antennas arranged on the E-plane to achieve broadband decoupling.Secondly,the decoupling cladding structure composed of array-antenna decoupling surface and composite decoupling surface is proposed for the circularly polarized MIMO antennas with the same rotating sense and the circularly polarized MIMO antennas with opposite rotating sense.The array-antenna decoupling surface plays the role of primary reflection,and the composite decoupling surface plays the role of optimal decoupling.With the help of the decoupling cladding structure,the relationship between the coupling cofficients in the x and y polarized directions is regulated by reflecting spatial wave.The experimental result show that the circularly polarized MIMO antennas with same rotating sense after decoupling satisfies the impedance matching and axial ratio requirements in a 11%fractional bandwidth with the coupling coefficient below-20 dB.Besides,the circularly polarized MIMO antennas with opposite rotating sense satisfies the isolation requirements in 9%fractional bandwidth.In addition,the decoupling cladding can improve correlation coefficient and radiation efficiency,and correct radiation pattern for antennas.The processing measurement verifys the decoupling ablitity of the decoupled cladding structure.Lastly,for the 1 ×2 circularly polarized antennas and 2×2 circularly polarized antennas,loading the metasurface above the array is poposed to decouple.The metasurface does not occupy the space between the antenna elements and controls space wave to decouple.After decoupling in 1×2 antennas,the deep coupling zero exists which isolation is improved by more than 30 dB and the pattern is optimized.In the 2×2 circularly polarized antennas,the element and metasurface are rotated to realized the coupling reduction between the ports.The measurement is verified that metasurface can reduce coupling.