Research For Jamming Of Radar Imaging With Time-Modulated Metasurface

At present,imaging radar as an important sensor to obtain information of sensitive targets,so the effective control of the radar characteristics of the target has become a key issue in the field of radar jamming.Although the active jamming is flexible in modulation,it has the disadvantages of easy exposure,and long response time;the passive jamming can respond in real time,but the jamming method is fixed once the jammer is made.Time-modulated metasurface(TMM),as a new type of electromagnetic modulation material,can be used for real-time modulation of electromagnetic wave amplitude and phase to achieve flexible passive jamming of imaging radar.Therefore,in this paper,we propose to conduct a study on the interference technology of phase-reconfigurable TMM to radar imaging.First,a 1bit reflective phase-reconfigurable time-modulated metasurface and its control module are designed and fabricated.In this paper,we design and process a 1bit reflective phase-reconfigurable metasurface unit with an operating bandwidth of 9.5GHz～10.7GHz,the reflection phase difference between the two states of the cell is within 180±20°,and the reflectivity is greater than 0.9.The phase difference measured is in good agreement with the full-wave simulation results.Secondly,a model for jamming of high resolution range profile(HRRP)by TMM is established,and the effect of two modulation methods on HRRP jamming is verified by electromagnetic simulation and experiment.The main aspects are as follows:(1)the periodic modulation causes false peaks in the HRRP.The range between the firstorder false target and the real target is the ratio of the time taken by the radar to transmit the broadband signal to the period of the metasurface modulation multiplied by the range resolution.When the duty cycle of the coded modulation pulse is 50%,the peaks at the real target position and the even-order false targets are suppressed.(2)The pseudo-random modulation can make the HRRP defocus with peak spreading with the envelope of sinc function,and the number of distance cells spanned by the first main lobe is related to the minimum pulse width of the modulated signal.In addition,it is experimentally verified that when the electromagnetic waves are incident vertically on the metasurface and coexist with scatterers of comparable scattering energy,they can also have an jamming effect on the HRRP thought.Finally,the model of jamming of inverse synthetic aperture radar(ISAR)with TMM is established,and the effect of two modulation methods on the ISAR imaging jamming is verified by electromagnetic simulation and experiment.TMM can achieve jamming of the azimuthal dimension of ISAR imaging when modulating the phase between different linear frequency modulated pulses during ISAR imaging time:(1)Periodic modulation can induce the appearance of false targets in the azimuthal dimension,and the false target spacing is related to the number of metasurface state switching in the imaging time;the faster the switching speed,the more azimuthally resolution cells the false targets are separated.(2)Pseudo-random modulation can reduce the peak amplitude of the real target in the azimuthal dimension,while forming jamming stripes.The electromagnetic simulation and the measurement results in the microwave chamber verify the above conclusions.