Design Of Broadband Metamaterial Absorber And Its Radar Cross Section Reduction Characteristics

Metamaterial absorbers have been widely used in electromagnetic stealth and electromagnetic protection,providing a new method and idea for Radar Cross Section(RCS)reduction.Traditional metamaterial absorbers have the disadvantages of poor oblique incidence and can only absorb electromagnetic waves propagating along a single direction.In this paper,broadband metamaterial absorbers with wide angle incidence and bidirectional absorption are designed to improve the directivity of the absorber.The absorptance of the traditional metamaterial absorber decreases with the increase of the oblique incident angle.In this paper,an equivalent circuit model of the metal resonator structure is established based on the transmission line theory,the metal split ring and the fan-shaped metal resonator are equivalent to the parallel circuit composed of resistance R,inductance L and capacitance C,and the dielectric substrate and air layer are equivalent to a transmission line,respectively.A broadband metamaterial absorber composed of double loop split-rings and a set of metal sector is designed according to the equivalent circuit model,the lumped resistors are inserted into the gaps of the loop split-rings and sectors for expanding the absorption bandwidth.The absorptance is larger than 0.9 in 1.61～4.45 GHz with the fractional bandwidth is 93.73%.The most important advantage of the designed absorber is that the absorptance can stay the absorptance at normal incidence as the incidence angle increases to 45° for both TE wave and TM wave.When the electromagnetic wave is incident vertically,the RCS reduction value of the absorber can reach 52.2 dB compared with the same size metal plate,and in the range of incidence angle[-45°,45°],it exhibits good RCS reduction characteristics.A sample is fabricated by using printed circuit board technology,and the electromagnetic characteristics of the absorber are tested by using free space method.The experimental results are in good agreement with the simulation results.The previous metamaterial absorber can only absorb electromagnetic waves propagating in a single direction.In this paper,a cross and hollow crosses and cross dipole are equivalent to RLC parallel and series equivalent circuit based on the transmission line theory,respectively,the ADS circuit simulation software is used to fit the equivalent circuit model of metal resonant structure,and a broadband bidirectional metamaterial absorber with a combined ABA structure is designed based on the equivalent circuit model,and two orthogonal I-shaped structures are pasted on both sides of the ultra-thin substrate(FR-4)instead of the metal plate for enhancing absorptance of the absorber.Simulated results show that absorptance of the designed absorber is larger than 0.9 in 1.43 GHz～2.51 GHz along forward and backward directions both under TE and TM polarizations.And the absorber exhibits excellent polarization insensitivity and wide angle incidence characteristics.Compared with the same size metal plate,the RCS reduction value of the absorber can reach 17.56 dB,and in the range of incidence angle[-30°,30°],it exhibits good RCS reduction characteristics.A 10×10 array sample is processed to verify the bidirectional absorption characteristics.In this thesis,a broadband metamaterial absorber with oblique incident enhancement and bidirectional absorption is studied based on transmission line theory,which is beneficial to promote the development of omnidirectional absorber technology and its wide application in electromagnetic compatibility and electromagnetic stealth.