Defected Ground Structure For Suppressing Mutual Coupling And Achieving Antenna Circular Polarization

The high level of mutual coupling in the antenna array will degrade the antenna element performance and the array performance,which are manifested in the following aspects: reducing the antenna efficiency,reducing the antenna gain,affecting the radiation pattern.Therefore,the study of mutual coupling suppression in the antenna array is significance important.In this paper,the authors use the band-rejection filter decoupling method and polarization rotation decoupling method to realize the mutual coupling suppression between antenna elements by designing a variety of defected ground structures(DGSs).By adding the defected ground structure to the microstrip antenna(array),we can achieve(1)the reduction of the mutual coupling between microstrip antenna elements;(2)the improvement of the cross-polarization deterioration of the antenna element in the decoupling antenna array;(3)the new type of circularly polarized microstrip antenna.The main contents and achievements of this thesis are as follows:(1)Research on the defected ground structure application in the antenna array mutual coupling suppression.The mutual coupling suppression performance of the antenna array is established by both the simulation and measurement.The change of the surface wave of the metal substrate and the radiating patch is studied,and the working principle of the band-rejection filter decoupling method is verified.Two types of DGS units,the U-shaped and S-shaped unit,are proposed and designed for achieving the mutual coupling suppression between antenna elements.The fabricated antenna elements and the defected ground structure are used to verify the simulation results.Both the measured and simulated results show that the U-shaped and S-shaped periodic defected ground structures can suppress the mutual coupling between antenna elements effectively and improve the radiation efficiency of the antenna elements.(2)The advantage of the defected ground structure compared with other types of artificial electromagnetic materials is that the aperiodic structure can also achieve the band-rejection filter characteristic in a certain frequency band.In order to realize the mutual coupling suppression of a miniaturized antenna array,a new fractal defected ground structure is proposed for the mutual coupling suppression between antenna elements.Through the analysis of structural parameters of the fractal defected ground structure,the working principle of the band-rejection filter is proved,and the design steps of the fractal DGS are given.The second and third iterative fractal DGS will suppress the electromagnetic energy transmission in the coupling field,realize the mutual coupling suppression between antenna elements,improve the radiation efficiency of the antenna element and increase the capacity of the MIMO system.(3)The authors also have studied the coupled polarization rotation method to achieve mutual coupling suppression by using the DGS.The coupled polarization in the coupling field is rotated 90° to reduce the received electromagnetic energy from the other antennas.A double helix-shaped DGS is proposed and designed to suppress the mutual coupling between antenna elements.This paper proposes another type of U-shaped fractal defected ground structure to realize the mutual coupling suppression between antenna elements by rotating the coupled polarization.However,the coupled polarization rotation method increases the antenna element cross-polarization values.For solving this problem,the arc-shaped DGS is studied to reduce the antenna cross-polarization in the decoupling antenna array.(4)A new type of single-feed circularly polarized microstrip antenna loaded with defected ground structure is proposed.The specific design method is adding the DGS to the ground plane below the radiated patch.By using the DGS,the cross-polarization of the linearly polarized antenna element is further increased to ensure that the cross-polarized level of the linearly polarized antenna is equal to the level of the main polarization.By adjusting the dimension of the DGS,the two orthogonal modes will have the same amplitude and 90° phase difference for achieving the circularly polarized radiation pattern.Based on this working principle,the author proposes a Y-shaped fractal DGS to design circularly polarized microstrip antenna.Both the simulation and measurement results show that the circularly polarized radiation pattern of the microstrip antenna can be realized by adding the second and third iterative fractal DGS to the ground plane below the radiated patch.