Research On Novel Frequency Selective Rasorber

Frequency Selective Surface?FSS?technology is widely used in radar stealth radome design.However,with the development of radar technology which is capable of receiving signals that are scattered to other directions by the detection target,it is imminent to research deeply on the Frequency Selective Rasorber?FSR?,which can transmit electromagnetic waves in passbands and absorb outside passbands.This paper focuses on the urgent needs of FSR in the current practical application.The main work is divided into the following three parts:?1?Firstly,an approach of designing passive multi-band FSR is described.With this method,a passive FSR with two passbands and three absorption bands is proposed,which has different resonant units on the upper and lower layers.The FSR structure achieves a transmission performance of-0.94dB and-0.2 dB at 5.92 GHz and 9.30 GHz,respectively.The bandwidth of|S₂₁|>-3dB is 1.92 GHz.The absorption rates of 93.7%,88.4%,and 95.5%are achieved at 2.94 GHz,7.84 GHz,and 10.89GHz,respectively.The bandwidth of the frequency range with absorption rates exceeding 80%is 1.98GHz.The FSR structure with two passbands and three absorption bands satisfies the application requirements of multi-band FSRs.There are transitional reflection bands between the transmission bands and the absorption bands of the FSR,and the highest value of|S₁₁|reaches-3dB.?2?In order to enhance the out-of-band stealth capability of the antenna and reduce the risk detected by enemy radar due to the high reflection of the transition band,this paper designs the second passive FSR with two passbands and three absorption bands,which makes|S₁₁|<-10dB in the whole work band.The upper and lower layers of the structure are based on the same resonant unit.The structure achieves a transmission performance of-1.6dB and-0.98dB at 7.26 GHz and 9.28 GHz,respectively.And the bandwidth of|S₂₁|>-3dB is 3.97 GHz;the absorption rates of 84.7%,77.1%and88.8%are respectively achieved at 4.18 GHz,8.59 GHz and 10.82 GHz,and the bandwidth of the frequency range with absorption rates exceeding 75%is 1.69GHz.The entire operating frequency band of the second FSR satisfies|S₁₁|<-10dB,which greatly improves the out-of-band stealth capability.?3?Finally,because the antenna is a strong scattering source,in order to enhance the in-band stealth performance of the antenna,this paper designs an active FSR with a controllable transparent window based on the research of passive FSR.The upper layer is actively controllable,while the lower layer is a passive bandpass FSS.Under TE polarization,when the PIN diode is turned off,the transmission performance at 4.28 GHz is good,whose insertion loss is-1.29 dB.The transmission band of|S₂₁|=-3 dB is 4.04-4.56 GHz.Two absorption bands are distributed on both sides of the transmission band.Absorption rates of 96.4%and 82.0%are achieved at 2.39 GHz and 5 GHz,respectively.When the PIN diode is turned on,the transmission window at 4.28 GHz is turned off,at which time the maximum value of|S₂₁|in this frequency band becomes-7.39 dB,the maximum value of|S₁₁|is-6.84 dB,and the absorption rates of the frequency band exceed 61.3%.The absorbing bands on both sides are almost unchanged.This active FSR combined with the structure stealth technology can realize the full-band stealth of the entire radar system when the antenna is not working,under the premise of satisfying the normal working condition of the antenna.In general,this paper designed the first FSR with two passbands and three absorption bands.After improving on it,the second FSR with two passbands and three absorption bands is designed.The second FSR achieves the design goal of|S₁₁|<-10dB in the whole work band,which enhances the out-of-band stealth performance of the antenna.Finally,an active FSR whose transmission window is adjustable is designed to improve the in-band stealth capability of the antenna.The design results of the three FSR structures have successfully achieved the expected design goals.