Research On Wideband Tightly Coupled Dipole Reflectarray Antenna

As the advance of 5G technology,the antenna which is the front-end of the communication system is required to be wideband while achieving high gain.Planar reflectarray antennas have outweighed many kinds of antenna because they have high gain and simple feed system besides the easy-fabrication.However,one of the biggest drawbacks is that they usually suffer from narrow bandwidth.In this paper,tightly coupled unit cells are employed to the design of a reflectarray,achieving a bandwidth of 2.5: 1,which is superior than most of the published reflectarrays so far.Under the instruction of tightly coupled theory and reflectarray theory,this paper aim to study the wideband tightly coupled dipole reflectarray antenna.The main work is as follows:1.A wideband dual-polarized tightly coupled reflectarray unit cell and true-time-delay line are both employed to achieve wideband property.The reflection phase of the unit cell is fairly linear from2 GHz to 5 GHz.The concept of "equivalent distance delay" is employed which we use to compensate the spatial distance delay of a unit cell in a frequency band.The reflectarray are consisted of 21? 21 unit cells.The measurement results show that the antenna gain varies from 11.3d Bi to 21 d Bi and the cross-polarization discrimination ratio is larger than 15 d B in the frequency band of 2-5 GHz.2.Aiming to resolve the situation where the equivalent distance delay of 2 GHz deviates from a design line,a variable-coupling-capacitance method is proposed.The coupling capacitance between a unit cell and its neighboring unit cell is determined according to its position in the reflecting surface.As a result,the equivalent distance delay in 2 GHz is more converged,resulting a reduced phase error.The equivalent distance delay at other frequencies remain mainly unchanged,which means the performance in other frequencies is not deteriorated.After measurement and comparison,the gain of the variant-coupling-capacitance tightly coupled dipole reflectarray antenna is increased by 3 d B at 2GHz,with the corresponding aperture efficiency improved by 21.6%.The aperture efficiency in 2 GHz is increased more than other frequencies,which verifies the effectiveness of this method.