Research On Metasurface And Its Application In Lens Antenna

In wireless communication systems,antenna design is critical for reducing system size and complexity of RF signal post-processing.Therefore,beamforming antennas,beam scanning antennas,and multi-beam antennas have received more and more attentions.The traditional phased array antenna system is undoubtedly an ideal solution to achieve the above functions.However,in the microwave and millimeter wave frequency bands,phase shifters and attenuators in phased array antenna systems are costly,have low energy efficiency,and are difficult to widely apply.Common alternatives are passive array antennas and parabolic antenna systems(controlled by servomotors).However,with the increase of the antenna elements,the feeding network will be very complicated and bring serious losses.Although the parabolic antenna system has excellent performances,it is relatively large and heavy,which is not conducive to integration,and it also has high requirements for the motor servo system.In the past decade,metasurfaces have been widely used in the electromagnetic field for ultra-thin electromagnetic lenses(concave lenses,convex lenses,etc.),programmable reflective surfaces,reconfigurable frequency selective surfaces(FFS),and three-dimensional imaging.Metasurfaces have the ability to control the polarization,propagation,and spatial distribution of electromagnetic waves.Therefore,combining electromagnetic surfaces with antennas will further improve the antenna's ability to control the beam.This paper first designs a class of highly efficient metasurfaces,physically characterizes them,and studies their polarization control and beam steering characteristics.Then,based on the Fourier transform principle between the far field and near field,the metasurface is combined with a feed antenna to form a beam reconfigurable lens antenna.In general,the main contribution of this article can be concluded as the following points:1.Based on the theory of multi-mode resonance,a highly efficient electromagnetic surface is designed.The electromagnetic surface is anisotropic,and can be used to control the polarization,the conversion between the linear polarization and the circular polarization,and PB(Pancharatnam-Berry)phase.An impedance network is used to accurately characterize the transmission characteristics of the unit,and a dual-polarized lens antenna design is implemented using the electromagnetic surface characterization model.The results show that the dual-polarized lens antenna has a bandwidth of more than 15%,port isolation of-25 d B and a cross polarization ratio better than-20 d B.2.A parabolic phase-compensated lens antenna is proposed for beam scanning,and its phase error was analyzed,and its beam scanning capability is compared with that of a common lens antenna.The results show that the scheme has more stable phase error and better beam scanning ability during scanning.The beam scanning lens antenna is designed.Experimental results show that the antenna has a beam scanning capability of ±60°.An elliptical rotating parabolic phase compensation lens antenna is further designed.The antenna can realize two-dimensional beam scanning based on the two-dimensional phase gradient theory.Experiments prove that the two-dimensional beam scanning lens antenna has a two-dimensional beam scanning capability of ±55° half-space.3.Designed a high-efficiency resonant electromagnetic surface unit with reversible phase.This unit is based on the feeding principle of via probes.By rotating the top patch,the relative position of the feeding point can be changed to achieve 180 ° phase reversal.The phase transmission limitation of the cascade structure is broken,and the working bandwidth and phase coverage of the electromagnetic surface are extended.By using the phase inversion characteristic of the unit,a lens with a step change in phase can be conveniently designed.The lens can realize the transformation of Gaussian distributed energy to Sinc function energy distribution.Then,using a Gaussian energy distribution feed,combined with a phase step change electromagnetic lens,a lens antenna with a beam width of 60o is designed.Polarizations applied to V(vertical)polarization and H(horizontal)polarization are further designed.Results show that the antenna can achieve both V-polarized and H-polarized radiation,with lower side lobes and a cross polarization ratio better than-30 d B.4.The fan-beam lens antenna is extended and the switching,methodology of different beam widths is derived.Based on the theory,fan-beam antennas with different beam widths are designed.And the high-gain pencil beam and fan-beam switching schemes are simulated and verified.Results show that using this theory,fan beam lens antennas with beam widths of 60o and 90o can be realized,and high-gain pencil beam and 60o fan beams can be switched electronically.5.Design an all-metal structure fan beam antenna for microwave backhaul central station.The antenna is based on the secondary radiation effect of the surface current by the periodic metal slot structure.The structure is used to adjust the near field of the metal horn so that it meets the near field conditions required by the fan beam(Europe ETSI EN 302 085 V1.2.3 Standard class CS2 series and class CS3 series).Then the antenna was verified experimentally.The final results show that both types of antennas meet the standard requirements of class CS2 and class CS3.Among them,the class CS2 standard antenna is lighter and thinner,and the class CS3 standard antenna has better performance.