Research On RCS Control Technology Based On Spectrum Shifting

With the development of radar technology,a large number of technologies against radar detection have appeared at the same time,and the use of radar absorbing materials is still the most widely used method.The emergence of electromagnetic metamaterials has greatly improved the absorption bandwidth,wide angle of incidence and absorption efficiency of various types of absorbing materials.However,it is difficult to meet the complex and variable electromagnetic environment.The electromagnetic tunable characteristics of the electromagnetic metamaterial can be used to design the reflective modulation board to realize the spectrum shifting of the radar wave.This method has advantages in flexibility and real-time performance compared with the conventional radar absorbing material.The first part of this thesis introduces the principle and classification of radar absorbing materials,and the research status of absorbing structures based on electromagnetic metamaterials.The main research content in this thesis is developed by the reflective modulation board based on electromagnetic metamaterials.The second part is based on the reflective modulation board to study the spectrum shifting of the radar signal.Two design ideas for modulation signals are proposed,in which it is easier to move the reflected signal spectrum out of the radar receiving bandwidth.The reflective modulation board consists of an active frequency selective surface(FSS),a dielectric layer and a metal backplane.FSS can be switched between total reflection and total transmission by changing its impedance,ideal two-phase modulation of the incident wave can be achieved and the power of the reflected wave is greatly reduced.CST simulation results show that the reflective modulation board can absorb more than 90% of energy at 0.6-0.75 GHz and 1.4-2GHz,the measured data shows that it can produce the effect of spectral shifting to the reflected signal,which is reduced by 10 dB at the original frequency.In the third part,the characteristics of radar echo modulated by the reflective modulation board are studied,and the time domain characteristics of the reflected wave through the matched filter are analyzed.Both theory and simulation prove that the receiver cannot detect the target information when the modulation frequency is greater than the radar bandwidth;when the modulation frequency is less than the radar bandwidth,not only the target information disappears but also a plurality of false targets will interfere with the judgment of receiver.Finally,the design method of modulation signal in random discrete state is proposed,which solves the problem that the ideal modulation board is difficult to apply in practice.The experimental results show that the proposed method can make the non-ideal reflector close to the effect of the ideal reflector.The characteristics of radar echo are also consistent with the ideal situation,more false targets will appear when the modulation frequency is less than the radar bandwidth.