| Radar cross section(RCS)is the key concept in radar stealth technology.By reducing the RCS of the target,the probability of being detected and tracked can be reduced,thereby enhancing its survivability.For aircraft,the cockpit,radar cabin,and inlet are their typical strong scattering sources,and their commonality is that they have strong scattering sources such as cavity scattering.Therefore,research on the RCS reduction technology of an electrically large open cavity can provide technical support for the control of strong scattering sources such as aircraft cockpits,radar cabins,and inlets,leading to improve its overall RCS performance.In this dissertation,a series of studies have been carried out on the RCS reduction technology for cavity structures.Based on the phase regulation mechanism of the metasurface for electromagnetic waves,the scattering control of the backward echo of the cavity structure is realized,thereby reducing its RCS.Firstly,the RCS reduction design method for the dihedral corner structure is studied.The research results are used as the research basis,which provides technical support for the subsequent research on RCS reduction of square cavity,circular cavity and S-inlet cavity.Secondly,the design methods of low RCS concave structures with ultra-wideband angles and low RCS square cavity structures with ultra-wideband angles are proposed.Finally,the phase gradient metasurface(PGM)and the phase cancellation metasurface technology are extended to the high-temperature cavity and the S-inlet cavity structure,respectively,and the low RCS design of the corresponding structure is realized.The main research contents and conclusions of this dissertation are as follows:(1)The design of metasurface-loaded low-RCS curved targets based on phase cancellation and phase compensation technology is studied.Aiming at the dihedral corner structure,a PGM based on a phase cancellation mechanism is proposed to reduce the dihedral RCS.Based on the phase cancellation mechanism,the guiding formula for lowRCS dihedral is derived,which is directly used to deal with the problem of wave path difference introduced by dihedral.When the operating frequency is 5 GHz,the RCS reduction of the dihedral is more than 10 d B.The proposed dihedral with PGM also has excellent angle insensitivity,ranging from 0° to 75°.In order to further expand the bandwidth,a checkerboard polarization conversion metasurface(CPCM)for reducing the RCS of the dihedral structure is proposed based on array theory.By loading CPCM on both sides,wideband and wide-angle RCS reduction are achieved,the fractional bandwidth of RCS reduction of 10 d B is more than 70% under Transverse Electric(TE)and Transverse Magnetic(TM)polarization,and it has good RCS reduction performance from 0° to 90°.Aiming at the concave structure,a design method for a low-RCS concave checkerboard metasurface based on phase compensation technology is proposed.The concave surface is equivalent to the octagonal prism structure,and the corresponding phase compensation is performed on the metasurface unit in the non-central region.Combined with the array theory,CPCM is proposed to load the inner partition of the concave octagonal prism structure.Under normal incidence,the fractional bandwidth of RCS reduction at 10 d B is 120.99%.Under oblique incidence,10 d B RCS reduction in the wide angle range of 0° to 34° is achieved,and the ultra-wideband and wide-angle RCS reduction performance of the concave structure is realized.(2)The design of metasurface-loaded low RCS cavity based on array theory and the orthogonality principle is studied.According to the array theory and the principle of orthogonality,the phase-cancelling metasurface structure(PCM)composed of polarized reflectors is loaded on the two sides of the inner and outer sides of the square cavity dihedral structure.The fractional bandwidth of 10 d B RCS reduction is more than 68%under TE and TM polarization,and the ultra-wide angle RCS reduction from-180° to180° is realized in oblique incidence.Based on the square cavity dihedral design results,according to the array theory and the principle of orthogonality,PCM is loaded on the three sides of the inner wall and the three sides of the outer wall of the cavity structure to achieve broadband and ultra-wide angle RCS reduction of the cavity structure.The fractional bandwidth of 10 d B RCS reduction under TE and TM polarization is 70.77 %and 52.83 %,respectively,achieving broadband RCS reduction.Moreover,the ultra-wide angle RCS reduction in the angle range from-180° to 180° is realized in oblique incidence.(3)The application design of a low-RCS cavity based on metasurface loading is studied.The application of a high-temperature cavity is explored,and a typical metasurface structure composed of dielectric substrate sandwidched by square metal patches and the metal ground plane is proposed.Under the normal incidence of a 5 GHz plane wave,the main lobe is directionally scattered to 41 degrees,which effectively reduces the backward RCS.Its electromagnetic properties in high-temperature environments are further studied.The conductivity of the metal layer zirconium boride changes linearly with temperature,which have little effect on the electromagnetic transmission properties of the metasurface.For the S-shaped cavity structure,various schemes of metasurface loading are explored.Among them,the scheme of loading the left,right,and bottom of the inner wall of the S-shaped cavity structure based on orthogonality and array theory is the optimal one,and the wide-angle RCS reduction of-80 to 80 degrees is realized.In summary,this dissertation realizes the RCS reduction of the broadband ultra-wide angle of the dihedral corner structure.Based on this result,the ultra-wideband wide-angle RCS reduction of the concave structure and the ultra-wideband wide-angle RCS reduction of the cavity structure are effectively realized.Then it is extended to the high-temperature cavity and S-inlet cavity structures.The orthogonality principle,combined with the array theory,is effective for the electromagnetic scattering control of complex targets such as dihedrals,cavities,and S-inlet cavities.In general,this research provides technical support for the application of metasurfaces to target RCS control.It also puts forward a new development direction for the electromagnetic scattering control of cavity targets. |
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