Design Of Rasorber Based On Frequency Selective Surface

Frequency selective surface(FSS)is a kind of two-or three-dimensional periodic array structure with special electromagnetic filtering characteristics.In the military field,FSS has been widely used in the development of radome to improve the stealth performance of various weapons.The traditional design method of FSS is mainly based on artificial experience.To some extent,its design cycle is long,and more importantly,it's hard to obtain the optimal structure parameters corresponding to the optimal filtering responses.With the application of various stochastic optimization algorithms,the problem of optimal structure parameters has been effectively solved,but the problems of low optimization efficiency and long design cycle still exist.Furthermore,for the FSS-based radome,due to the existence of reflected waves,it can only achieve mono-static radar cross section(RCS)reduction,but has no effect on multi-static radar system.Focusing on the above problems,this paper starts with the optimization method of FSS and investigates the stochastic optimization algorithm suitable for the fast optimization design of FSS.Meanwhile,aiming at the problem of multi-static RCS reduction,the design method of frequency selective rasorber(FSR)with the characteristics of in-band transmission and out-of-band absorption is studied.The main research contents are as follows:(1)Aiming at the problems of premature and slow convergence of stochastic optimization algorithm in FSS design,four strategies including better particle initialization,acceleration coefficient dynamic adjustment,search space reset,and particle density control are proposed to improve the particle swarm optimization(PSO)algorithm.By applying the algorithm to the optimization design of square loop FSS,the high efficiency of the improved PSO algorithm is validated.Compared with the existing literature,the number of iterations can be reduced by nearly 40% on the premise of ensuring the optimization accuracy.(2)Around the problem of multi-static RCS reduction,three typical FSR structures are designed.Based on the equivalent circuit analysis,the method of reducing FSR's in-band insertion loss(IL)is analyzed,which is by introducing the parallel LC resonator into FSR's top resistive sheet.On this basis,from the perspective of improving FSR's grating lobe problem and out-of-band absorption performance,the FSR with high in-band transmission at low frequency and wideband absorption at high frequency is designed firstly by utilizing the metallic spiral microstrip and the highly selective bandpass FSS loaded with capacitive metallic patch.An IL of 0.3 dB as well as an 84% absorption bandwidth is realized.Secondly,based on the tortuous structure,the FSR with wideband transmission response at high frequency and ultrawideband absorption response at low frequency is synthesized.The fractional bandwidths of its transmission and absorption bands are 19.6% and 107.9%,respectively.By meandering the metallic microstrip to extend its resonance path,the design of parallel LC resonator with larger equivalent inductance and smaller equivalent capacitance is completed,and then the wideband transmission response of FSR's resistive sheet is realized.Moreover,FSR's periodicity is also reduced significantly,which in turn improves the grating lobe problem and the stability of FSR.Subsequently,from the point of view of simplifying FSR's structure,the parallel LC resonator similar to the interdigital structure is applied to design the two-sided wideband absorption FSR.The in-band IL of its transmission band is reduced to only 0.19 dB,and the 10 dB reflection reduction bandwidth reaches 119.5%.For verification,FSR prototypes have been fabricated and measured,respectively.The measured results are in good agreement with the simulated ones,which verifies the effectiveness of the proposed FSRs.This paper starts from FSS's optimization method,and puts forward an improved PSO algorithm suitable for the fast optimization design of square loop FSS.The proposed three typical FSR structures have achieved low in-band IL,wideband absorption and better stability.The above research results have certain guiding significance in the field of FSS and FSR structure optimization design.