Investigations Of Lens Antenna And Radome Based On Metamaterial

As a kind of artificially-designed structure composed of a series of sub-wavelength unit cells,metamaterial has unique electromagnetic properties which can't be realized by natural materials.By tailoring the shape or size of metamaterial unit cells,arbitrary permittivity and permeability can be achieved,which means electromagnetic waves can be manipulated flexibly.Therefore metamaterials attract considerable attention and many significant achievements have been made in different fields.The main contents of the thesis are as follows:1.The constitutive parameters of two asymmetric bi-anisotropic media are calculated based on inverse cosine method,including the effective electric permittivity,magnetic permeability,and the magnetoelectric coupling coefficient,from the reflection and transmission coefficients.This method can also be used to retrieve the parameters for symmetric metamaterials.It is an amendment to the theory of the equivalent medium.2.A planar wave-front transformation lens is designed by using gradient-index metamaterials,which is composed of isotropic and inhomogeneous unit cells,one can get the well impedance-matching with free space,and control the wave radiation simultaneously.As an example,we present a compact highgain and high aperture-efficiency lens antenna working in broadband from 8 to 12 GHz.The consistence between simulational and experimental results demonstrates the excellent performances of the lens antenna,which has higher directivity in H plane and better impedance-matching than those of traditional optimal H-horn antenna.3.Based on impedance-matching theory,a Bessel lens antenna is designed and feed by the H-horn antenna.The focal point of the lens coincides with the phase center of the H-horn.The result shows the excellent VSWR with lower than 1.35 in the whole X band.4.Based on the artificial electromagnetic surface,two types of bi-functional radome are designed,one is the dual-band high transmission radome and another one is the active radome.The former can realize dual band transmission characteristics with large incidence angles.The later can achieve transmitted and reflected mode by switching working status of a diode between the “ON” and “OFF” states at 28 GHz.Under the "open" state,the insertion loss of transmission is less than 1d B,while in the "off" state,isolation of reflection is greater than 20 d B with bandwidth of 2.5GHz.