Research On Metasurface Based Circular Polarization Antenna And Its Array

Circularly polarized antennas have important application values in satellite communication and radar measurement and control,and the development of electromagnetic metasurfaces theory and technology has introduced a new insight to the design of circularly polarized antennas with high-performance.There are two main ways to apply metasurfaces to antennas.First,applying a metasurface as an auxiliary structure to antenna can satisfy the requirement of high gain,wide beam and high isolation.Second,using a metasurface as the radiation structure of an antenna can increase the effective radiation aperture and reduce the quality factor,thereby achieving excellent antenna performance such as high gain,low profile and wideband.Based on the second design idea,this thesis studies the design of circularly polarized metasurface antennas.The target of this thesis is to expand the impedance bandwidth and axial ratio bandwidth of the circularly polarized antenna,with maintaining a low profile and high gain.The main research content of this thesis is as follows:1.A circularly polarized metasurface antenna has been proposed with low profile,high gain and high cross-polarization discrimination based on L-shaped probe feed.Firstly,a low-profile,high-gain antenna element is designed by using the L-shaped probe feeding method and combining the corner cut metasurface structure.Then,in order to improve the circular polarization performance of antenna,a 2×2 array is formed by sequentially rotating,and a microstrip line feed network and a strip line feed network are respectively used.Due to the integrity of the floor,the antenna array has a high front-toback ratio and cross-polarization discrimination.2.The axial ratio bandwidth of the antenna is widened and the gain is improved by means of differential feeding.Two L-shaped probes and a T-shaped power divider are used for differential feeding of the antenna unit.Compared with the single-feed method,this approach of feeding increases the surface current in the same direction on the metasurface,so the antenna has a wider axial ratio bandwidth and higher gain.3.A low-profile broadband circularly polarized metasurface antenna based on sequential rotation is proposed.Both the radiation structure and the feed structure of the antenna are arranged in a sequential rotation.This design leads to a more consistent direction of the surface current on the metasurface,which reduces the mutual interference between the patch units,and thus a wider working bandwidth of the antenna is acquired.A one-to-four broadband feed network is designed and applied to the antenna unit,which further verifies the broadband characteristics as a result of the sequential rotation arrangement.4.A circularly polarized metasurface antenna array with bidirectional radiation is designed by means of characteristic mode analysis.Firstly,by analyzing the characteristic mode of the metasurface elements of the antenna,a suitable slot-coupled microstrip line feed structure is selected for feeding.Then,the bidirectional circularly polarized antenna array is obtained,which radiates left-handed circularly polarized waves in the forward direction and radiates right-handed circularly polarized waves in the back direction.