Design Of Wideband/Absorptive/Miniaturized Frequency Selective Surface

Frequecncy Selective Surface(FSS)is a periodic structure composed of metallic patch and dielectric substrate elements,which has selective transmission and reflection characteristics for electromagnetic waves in space,so it is often used in radar radome,electromagnetic stealth and other electromagnetic fields.With the development of electromagnetic technology,the demands and requirements of FSS are increased correspondingly.This thesis studies some important properties of FSS,and designs a wideband high-transmission FSS with angular stability and double sharp sidebands,an absorptive/transmissive frequency selective surface(ATFSS)and a miniaturized FSS with angular stability.The main research works of this thesis include the following aspects:1.The working principle of FSS is introduced.By means of equivalent circuit or formula derivation,the principle and method of FSS to realize broadband,absorption and sharp sideband are discussed.Then,the characteristics of FSS about miniaturization,angular stability and high transmission are described and analyzed.These provide theoretical guidance for designing FSS.2.In order to solve the problems of large insertion loss and poor angular stability of wideband FSS with double sharp sidebands,the 3D wideband FSS with double sharp sidebands composed of metallic waveguide,metallic column and metallic patch is optimized.The waveguide in the original structure is replaced by the dielectric substrate printed with metallic grids,which reduces the interconnection of FSS elements and reduces the insertion loss of passband to achieve high transmission.The profile of wideband FSS with double sharp sidebands is high and it is sensitive to the change of incident wave angle.When the angle of incident wave increases,the stopband of structure at high frequency will change to passband.By printing two groups of 2 ?2 resonant metallic square rings on the upper and lower surfaces of the dielectric substrate printed with metallic grids,the structure will continue to be stopband at high frequency with the increase of incident wave angle,which improves the angular stability of the structure.Finally,a wideband high-transmission FSS with angular stability and double sharp sidebands is designed.The simulation results show that the FSS has a-1d B bandwidth of 5.86 GHz to 13.4GHz with the relative bandwidth of 78.3% and the structure shows stable performance when the incident angle of TE polarized electromagnetic waves range from 0° to 45°.Then,the designed structure is manufactured and measured,and the measured results show good consistency with the simulation results.3.In order to solve the problem of low absorption rate of Absorptive/Transmissive Frequecncy Selective Surface(ATFSS)with double transmission bands at high frequency,one resonant metallic ring is designed on the lower surface of the dielectric substrate which is printed with metallic grid loaded resistors on the upper surface and the other one is designed inside the metallic grid.This structure called lossy layer has three absorption bands.The transmission layer with double transmission bands is realized by designing two square ring slots with different sizes on the metallic floor.The transmission layer is placed under the lossy layer with reasonable height of the air layer which improves the absorption rate of the lossy layer.The whole structure has three absorption bands and two transmission bands,and this ATFSS with double transmission bands shows good absorption at high frequency.The simulation results show that the transmission coefficient higher than-3d B ranges from 4.97 GHz to 5.73 GHz and 7.45 GHz to 7.91 GHz.The reflection coefficient lower than-10 d B ranges from 3.31 GHz to 10.42 GHz.The absorption bands with absorption rate greater than 80% range from 2.98 GHz to 4.35 GHz,7.07 GHz to 7.32 GHz and 8.52 GHz to 10.41 GHz.4.In order to solve the problem of large element size and poor angular stability of the traditional FSS,a miniaturized FSS with angular stability is designed by the bending metallic patches and multi-layer metallic vias.Based on the closed ring structure connected by open metallic rings and metallic vias,the design of miniaturized structure is realized by introducing two layers of reverse "S" shaped bending metallic patch and two layers of dielectric substrate with metallic vias and bending the opening metallic rings in sunken way.Miniaturization helps to improve the angular stability of the structure.The simulation results show that the FSS resonates at 1.53 GHz,the element size is 0.026?,and the structure shows stable resonance for incident angle ranging from 0° to 80°.