Research And Design Of Broadband Frequency Selective Rasorber With Absorption And Transmission

With the development of science and technology,military units such as aircraft and missiles will be detected by radio technology and radar detection technology,so that the survival rate of military units will be greatly reduced,so radar stealth technology becomes particularly critical.Various military units can improve their combat and survivability on the future battlefield with the support of radar stealth technology.The Frequency Selective surface based radome has a stealth function.It can achieve low insertion loss wave penetration in the required working frequency band,and reflect electromagnetic waves in the unwanted working frequency band to a direction away from the incoming waves,thereby achieving the function of stealth,but the electromagnetic waves reflected by the FSS are most likely to be detected by dual-base or multi-base radar,or it may be detected again.To solve this problem,the concept of Frequency Selective Rasorber was proposed.Different from FSS,FSR has the electromagnetic characteristics of low insertion loss in-band and wave-absorbing out-of-band.It has advantages in multi-station and wide-angle RCS reduction.Based on the working principle of FSR,this thesis designs various FSRs with wideband frequency response.The main work content can be summarized as the following:(1)The first chapter introduces the classification and application of absorbing materials and the current research status of outstanding scholars at home and abroad.The second chapter discusses the related theories of FSS and FSR,which lays the theoretical foundation for the research and design of various broadband FSRs later.(2)In Chapter 3,two FSRs with low frequency transmission/high frequency bandwidth absorption are designed.The transmission band of the first structure |S21|<3d B is1.15?1.6GHz.|S11|>10d B absorption band is 7?35GHz,The model unit size is 3mm,so when electromagnetic waves are incident on the surface of the FSR at a large angle,the model can still maintain good wave absorption performance,and the model is centrosymmetric,so the frequency response under TE and TM polarization is basically the same.The second structure is compared with the first structure,although the absorption band bandwidth is reduced,|S11|>10d B absorption band is 5.51?21.35 GHz.However,the transition band between the transmission band and the absorption band is narrower and the transmission band becomes wider,and the insertion loss in the transmission band is also small.Its |S21|<3d B transmission band is 0?3.82 GHz.The second model is miniaturized,and the period of the FSR unit is reduced by 2mm by folding the branches of the dipole.The miniaturization process not only improves the angular stability of the model,but also suppresses the generation of grating lobes.The transmission band of the miniaturized model is almost the same as the model before miniaturization.|S11|>10d B absorption band is 6.7?29.5GHz,The absorbing bandwidth has been broadened compared with the model before miniaturization.(3)In Chapter 4,three FSRs with low frequency absorption/high frequency bandwidth transmission are designed.The first structure uses the principle of 1/4? short-circuit stub to realize the function of low-frequency wave absorption/high-frequency wave transmission.|S21|<1d B transmission band is 8.1?12.1GHz,|S11|>10d B absorption band is 2.2?6.3GHz.FSR has good angle and polarization stability.FSR has also been processed and tested.The actual frequency response is basically the same as the simulated one.Under the second structure TE polarization,the transmission band with |S21|<1d B is 8.5?17.4GHz,and the absorption band with an absorption rate of 80% is 4?6GHz.Although the transmission bandwidth is much larger than that of the first structure,due to the asymmetry of the model,the S-parameters under TE and TM polarization are basically different,so the second model is only a single-polarization wide-transmission FSR.The third structure achieves the stability of S-parameters under different polarizations on the basis of the second structure,and compared with the first structure,the transmission band is wider,and it can maintain a good frequency response even when electromagnetic waves are incident at a large angle.