Research On Radiation And Scattering Regulation Of Metasurfaces

Metasurfaces are two-dimension(2D)artificial electromagnetic(EM)structures composed of periodic or aperiodic sub-wavelength unit-cells.Due to the strong ability in EM wave manipulation,metasurfaces have found wide applications in electronic countermeasures,microwave imaging,and wireless communications.By introducing tunable devices such as diodes and amplifiers,metasurfaces can obtain reconfigurable functional properties,thereby manipulating spatial EM waves dynamically.Focusing on the scattering properties of metasurfaces,this thesis conducts research on the amplitude and phase controllability of metasurfaces from the perspectives of polarization,bandwidth,control range,and so forth.In addition,as the main scattering source on the airborne platform,the antenna greatly affects the overall scattering performance of the equipment.Traditional design methods are difficult to well balance the radiation and scattering performances of antennas,while metasurfaces with scattering controllability provide a new solution to the dilemma.Based on this,a design method of metasurfaces is proposed in this thesis that integrates the radiation and scattering control.The main contents are summarized below:1.A dual-polarization wideband metasurface with simultaneous amplitude and phase control ability is designed.Two PIN diodes are integrated into the unit-cell to independently manipulate the EM responses of x-polarized and y-polarized incident waves.In the frequency band of 8～12GHz,the reflection phase can achieve 1-bit manipulation by switching the ON and OFF states of the diodes.Meanwhile,the reflection amplitude can be dynamically regulated from-15 d B to-2d B by controlling the bias currents of the diodes.Based on the phase regulation method,beam deflection and diffuse scattering are realized by setting two coding sequences on the metasurface.With the amplitude regulation approach,the incident wave can be absorbed effectively.In addition,the Radar Cross Section(RCS)of the metasurface is reduced by more than 10 d B in these cases.2.A reconfigurable metasurface with independent control of reflection amplitude and phase is proposed.Two types of diodes are integrated into the metasurface for independent regulation.Specifically,the reflection amplitude of the metasurface can be controlled by adjusting the bias currents of the PIN diodes,and the reflection phase can be controlled by tuning the bias voltages of the varactors.Therefore,arbitrary reflectivity of the metasurface can be obtained by controlling the two diodes jointly.The reflection amplitude and phase of the metasurface can range from-13 d B to-2.8d B and 0° to 360°,respectively.Based on such good features,the beam deflection is realized by applying gradient phase distributions along the metasurface,and low side-lobe level(SLL)scattering patterns are simultaneously achieved by setting Taylor amplitude distributions.3.Two metasurfaces(denoted M1 and M2)with simultaneous radiation and scattering controllability are designed,in which the PIN diodes are introduced to solve the contradiction between radiation and scattering regulation.For M1,effective radiation is achieved in the frequency band of 7.6～10GHz,and the scattering amplitude can be dynamically regulated from 7.5GHz to 10.6GHz.M2 can radiate effectively from 7.3GHz to 10.1GHz,and the scattering phase obtains 1-bit manipulation in the frequency band of9.7～11.4GHz.Both of the metasurfaces can reduce the in-band RCS of the antenna while ensuring radiation performance,which may find vast applications in antenna stealth and electronic countermeasures with the advantages of low profile and flexible regulation.