Radar Target Scattering Characteristics Modulation Research Based On Active Metasurface

Metasurfaces is a new type of artificial electromagnetic material formed by periodic or non-periodic arrangement in the sub-wavelength size range,which not only has the advantages of thin thickness,light weight,low loss and easy integration compared with traditional three-dimensional electromagnetic metamaterials,but also can be flexibly adjusted by changing the shape of the metasurfaces unit and the array arrangement,so as to regulate the amplitude,phase,polarization and frequency of electromagnetic waves.It has the potential to be widely used in the field of electromagnetism because of its physical quantities such as amplitude,phase,polarzation and frequency.As the technology of metasurfaces continues to mature,the determined phase and polarization of the metasurfaces structure lacks the flexibility to dynamically regulate the electromagnetic response,therefore the integration of tunable components or materials into the metasurfaces unit to form an active metasurfaces has become a current research hotspot.This paper will focus on the scattering characteristics modulation of active metasurfaces structures,introducing the concepts related to radar scattering cross section and Doppler effect,combining generalised Snell’s law and time-domain finite difference analysis methods,analysing the principle of active reflective metasurfaces modulation of electromagnetic wave phase,and carrying out radar scattering cross section(RCS)enhancement techniques based on phase gradient metasurfaces and phase tunable metasurfaces based on Micro-Doppler echo generation technology based on a phase-adjustable hypersurface is investigated,as follows:(1)A design method based on active phase-gradient metasurfaces(PGMs)is proposed for enhancing the RCS of special obtuse dihedral angles,which consist of a planar structure covering the metasurfaces and a curved curved surface structure.Using a varactor diode loaded on the super-surface cell,the metasurfaces cell is excited by an external voltage source to tune the phase range close to 360°.By building a rational feed network,the metasurfaces array can be dynamically adjusted to the reflected phase under the excitation of an external adjustable voltage source.In turn,by designing a reasonable phase gradient,the beam deflection effect can be achieved,so that the electromagnetic waves incident on the obtuse dihedral structure can be reflected to the incoming wave direction,and finally the RCS enhancement can be achieved.Simulation results show that RCS enhancement is achieved over a wide angular range of-90° to 0° at the 10 GHz centre frequency point.The maximum enhancement reaches 30 d B around the-76°,-60° and-30° angles.overall RCS enhancement.is up to 15 d B.also,the overall design has some broadband RCS enhancement characteristics around the centre frequency of 10 GHz.(2)A technique for generating artificial Micro-Doppler echoes based on a phasetunable metasurface is proposed,and a theoretical study of echo modulation based on phasetunable metasurfaces as well as artificial Micro-Doppler generation is analysed.By introducing dual resonant points to the phase-tunable metasurfaces,the design not only overcomes the limitation of the conventional metasurfaces structure with a phase modulation range of less than 360°,but also expands the operating bandwidth of the phase-tunable metasurfaces.The design also uses an arbitrary waveform generator(AWG)as the voltage signal source for the metasurfaces structure in order to achieve continuous adjustment of the phase of the metasurfaces echo in the time domain for a rational and complete experimental solution.The implementation of a programmable vector network analys using host computer software is investigated to ensure continuous automated measurement and preservation of experimental data in the time domain.Based on the above theoretical and simulation analysis,as well as experimental measurements,the design achieves modulation of the echo phase in the frequency band range 3.1 GHz-3.3 GHz and the synthesis of artificial Micro-Doppler echoes.