A Study On Frequency Selective Rasorber

Frequency Selective Rasorber(FSR)is a periodic array structure and exhibits in-band transmission and out-of-band absorption characteristics instead of reflecting the out-of-band electromagnetic waves,which can be seen as a combination of traditional FSS and absorber.As a kind of electromagnetic functional material with space filtering/absorbing feature,it has a wide application prospect in communication security and military fields such as antenna,radome,stealth technology,etc.With the development of communication and radar system,FSR has become one of the research hotspots in recent years.In view of the defects of FSR in practical application,this paper makes an in-depth study of theories and technologies such as frequency tunability,profile compression and dual polarization of FSR.The specific innovative work is as follows:1.A frequency tunable FSR based on varactor is proposed: To meet the practical application requirements,an FSR based on varactor-embedded square-loop array is proposed,which realizes the frequency tunable characteristics.An equivalent circuit model is developed to explain the principle.Each layer has an embedded wire grid that provides the bias voltage for the varactors through metallic vias.Simulated and measured results show that by changing the bias voltage from 16 to 4 V,the center transmission frequency of the FSR can be tuned from 5.2 to 3.8 GHz continuously.The structure has the characteristics of low insertion loss,tunable transmission frequency and is easy to be extended to the dual-polarized one,which provides a solution for the tunable and reconfigurable stealth radome.2.An ultrathin 3-D FSR with wide absorption bands based on folded structure and ferrite material is proposed: To solve the issue that the profile of common 3-D FSR is difficult to reduce and the absorption bandwidth is narrow,a kind of 3-D FSR based on folded structure and ferrite material is proposed.The thickness can be greatly reduced by more than70% from the most reported designs.while it can still achieve an ultrawide absorption band and a passband with low insertion loss through bypassing the absorption path with a series LC circuit at the passband frequency.Simulated and measured results show that the absorption bandwidth is 164%,while the thickness of profile is only 0.016λL(λL is the free space wavelength corresponding to the lowest operating frequency).3.A 3-D FSR with low profile and wide absorption bands based on stepped impedance resonator is proposed: A new low profile 3-D FSR with wide absorption bands at both sides of the transmission window based on stepped impedance resonator(SIR)is presented.Band-stop FSS based on microstrip meander-line is used to instead the lumped components and simplify the design and production process.By establishing the equivalent circuit model,the operating principle and parametric analysis are given in detail.The measured absorption bandwidth is 128% and the thickness of profile is only 0.118λL.4.A dual-polarized 3-D FSR based on rotational symmetric structure is proposed:In order to solve the problem that 3-D FSR can only work in the single polarization state under normal circumstances,a solution based on rotational symmetric structure is proposed.The magnetic absorber is used to replace the traditional resistor to obtain the broadband absorption characteristics and a rotational symmetric structure is introduced to realize the dual polarization.The feature is realized by using SIR.Simulated and measured results show that the absorption bandwidth is 121.1% and the thickness of profile is 0.158λL.