Study On Frequency Selective Surface For Electromagnetic Waves Manipulation And RCS Reduction

In stealth design,stealth materials are usually used to further reduce the radar cross section(RCS)of targets on the basis of shape stealth.Stealth materials are mainly divided into absorption type and beam control type,most of which concentrates on the processing of the main beam of reflection.In practical applications,the target normally consists of multiple planes,and oblique incidence and multiple reflections inevitably occur.At this time,the main sources of echoes are backward side-lobes and main beam of multiple reflections.Absorbing materials have limited absorption effect on backward side-lobes,and the manipulated main beam in a broadband is uncontrollable after multiple reflections.Under this background,this paper takes frequency selective surface(FSS)as the basic research object,utilizing the metasurface design method and array antenna synthesis technology to realize the diversification of active beam control and RCS reduction under oblique incidence,and improves the reliability and functional diversity of FSS in stealth applications.The main contents of this paper are as follows:Firstly,a broadband passive phase gradient FSS is designed,and it is proved that the generalized Snell's law for metasurface is equally applicable to the design of FSS by simulation,fabrication and measurement.Based on this law,a beam-adjustable active phase gradient FSS based on PIN diode is designed,in which the phase of the corresponding unit can be switched between 0 and 180 degrees by changing the status of PIN diodes,and the equivalent circuit method is utilized to verify the design.The relationship between phase gradient,frequency and abnormal reflection angle is analyzed.It is proposed to change the phase gradient by controlling the number of electrified columns and further adjust the beam reflection angle.Full-wave numerical simulation shows that different modes corresponding to different numbers of electrified columns can achieve wide-angle beam steering.Taking dihedral angle as an example,the RCS reduction performance of FSS can be fully utilized by adjust the operating mode.Secondly,the low side-lobe FSS based on the amplitude-adjustable unit is designed.The amplitude of reflection coefficient under normal incidence changes with the resistance of loaded resistors but the phase remains unchanged.The FSS and the array antenna have the same two-dimensional periodical structure,so the low side-lobe synthesis of array antenna is utilized in FSS design,and the units with different amplitude are arranged according to the Taylor distribution,achieving significant side-lobes suppression under normal incidence and taking into account part suppression effect under oblique incidence.Numerical simulations show that monostatic RCS reduction of more than 10 dB in the angular range of 5-40° can be achieved at 8-12 GHz.In order to improve the absorption under normal incidence and the side-lobe suppression performance under oblique incidence,PIN diodes are used as variable resistors instead of fixed resistors.So the multifunctional FSS with strong absorption and side-lobe suppression is designed,and numerical simulation shows that monostatic RCS reduction of 10 dB in the angular range of 0-40° can be achieved at 8.5-11 GHz.