Design And Analysis Of Frequency Selective Surface With Phase Gradient

As an important method to improve the survivability of military weapons and enhance their combat capability,radar stealth technology has special significance for the development of China's military field.The key of stealth technology is to reduce the Radar Cross section(RCS)of the target.The introduction of phase gradient metasurface could freely control electromagnetic wave,and also provides a new way for RCS reduction.In addition,the Frequency Selective Surface(FSS)as a new type of absorbing structure has far-reaching effects on the application of radar stealth.This paper aims to design a absorbing FSS with phase gradient,which has excellent RCS reduction performance in the normal incident at 4-12 GHz.In this paper,the general Snell's law and the principle of phase gradient anomalous reflection are introduced.The design principle of phase gradient is derived from the theory of array antenna,which provides a theoretical foundation for the design of FSS phase gradient structure.At the same time,the equivalent circuit model of the FSS unit structure is accurately modeled,and the equivalent parameters are verified for the RCS reduction performance.Two FSS basic units of the anomalously reflective FSS phase gradient structure are designed by MATLAB-CST co-simulation method.The phase difference between the units is maintained about 180 ° at 4-12 GHz.Then several phase gradient structures are constructed with different arrangement and unit block composition,and the RCS reduction performance of different structures are analyzed.A one-dimensional FSS phase gradient structure consisting of 5*5 unit block is selected.The simulation results can obtain RCS reduction performance more than 15 dB at4.1-12 GHz,and the relationship between frequency and anomalous reflection angle is clarified.The principle of anomalous reflection is applied to the FSS structure loading resistance to constitute a phase gradient structure combining absorbing and anomalous reflection.Firstly,two FSS unit structures with stable phase difference are selected in the target frequency band.The RCS reduction performance of the one-dimensionalphase gradient structure is optimized by adjusting the resistance value.The simulation results show that the structure can achieve RCS reduction more than 10 dB in the range of 4.1-12 GHz,and achieve RCS reduction performance more than 20 dB at4.4-10.8 GHz.In order to theoretically prove the effect of anomalous reflection or the combination of absorbing and anomalous reflection on the RCS reduction,the particle swarm optimization algorithm is used to accurately extract the equivalent parameters of the FSS unit structures.The RCS reduction calculated by the equivalent parameters is basically consistent with the RCS reduction in the simulation results,which confirms the accuracy of the extracted parameters and the effectiveness of the phase gradient structure on the RCS reduction.Finally,the samples were prepared and the reflectivity of the samples was measured in a microwave darkroom by free space method.The measurement results of the anomalous reflection sample is basically consistent with the simulation results.The sample combined with absorbing and anomalous reflection is measured with reflectivity below-30 dB at 5.4-8.4 GHz.Therefore,applying the phase gradient theory to the absorbing FSS structure can simultaneously play a role in absorbing and controling electromagnetic wave,which has more excellent RCS reduction performance than the phase gradient structure with only anomalous reflection.