Reduction Control Technique Of Radar Cross Section For Cylinder With Phase And Amplitude Gradient Frequency Selective Surfaces

The key of radar stealth technology is to reduce the Radar Cross Section(RCS)of target.And X-band(8-12 GHz),as the usual working frequency of radar,is of special research significance.A new direction has been put forward for RCS reduction with Phase Gradient Frequency Selective Surface(FSS),while the Amplitude Gradient FSS,which is based on the sidelobe suppression effect by array antenna synthesis,points out a fresh method for backward RCS reduction under oblique incidence.The thesis aims at reducing the backward RCS of cylinder in X-band with Phase Gradient FSS and Amplitude Gradient FSS,whose main contents are as follows:Firstly,in this thesis,the generalized Snell's law and the phenomenon of phase gradient anomalous scattering phenomenon are introduced,in the meanwhile,the discretized expression of Taylor line source current under different sidelobe levels is deduced,which respectively provides the theoretical basis for the design of Phase Gradient FSS and Amplitude Gradient FSS.Moreover,the equivalent circuit method is used to realize the rapid design of the Phase and Amplitude Gradient FSS,and theoretical guidance is offered for the regional design by the equivalent analysis of the scattering characteristics of the metal cylinder.Secondly,a Phase Gradient FSS is designed,whose phase difference between two status is maintained at approximately 180° by resistors to form a certain phase gradient,which achieved anomalous scattering of electromagnetic waves so that the RCS could be reduced.-19.3 d B of RCS reduction for metal plate is is achieved in X-band,whose length is 300 mm.In the meantime,the surface current analysis of cylinder shows that specular scattering in ±15°makes up a large part of backward RCS.Therefore-12.2 d B backward RCS reduction for a metal cylinder is realized by loading Phase Gradient FSS in the ±17.2° region of the incident direction which is TM polarized.The experimental sample is made and the measurement results are in good agreement with the simulations.Thirdly,an Amplitude Gradient FSS is proposed,whose unit current is controlled by different resistors,consequently the Taylor line source current distribution is conformed in one dimension and reduces the RCS by suppressing the sidelobes.On account of the sidelobes,region in 20°-70° contributes to backward RCS as well.Thus-19.1 d B of integrated backward RCS reduction in X-band is achieved by loading the Amplitude Gradient FSS in the area of17.2°-71.6°,which is-6.9 d B more than Phase Gradient FSS.The experimental sample is measured in anechoic chamber and the results are consistent with simulations.