Reaserch On Improved Structures And Electromagnetic Manipulation Of Multiband Frequency Selective Surface

Frequency selective surface(FSS)is a kind of spatial filter,which is a two-dimensional periodic assembly of resonant structures,either as apertures in a thin conducting sheet or as metallic patches on a substrate,correspondingly with single or multiple band-pass or band-stop function,respectively.By virtue of their frequency selective characteristics,FSSs have been an important research focus because of their comprehensive applications,such as band-pass hybrid radomes,sub-reflectors of antennas,electromagnetic compatibility in microwave regions.In this dissertation,the multiple chooses band-pass or band-stop FSSs are choosen as the research object.Furtherly,the physical mechanism,design principles,fabrication and experimental verifications,by means of theory analysis,numerical calculations,electromagnetic manipulation and experimental measurements,are studied.The main work can be concluded as follows:1.Research on high selectivity and dual-band FSS.Based on the coupling technique of multlayers,we present a dual-band FSS by cascading three layers of arraies.The proposed FSS behaves high selective performance,operating X and Ku band,respectively.The equivalent cicuit model is constructed,to analysis the oprating mechanism of the FSS.The FSS has merits of wideband response,low insertion loss,and excellent angular stability.The-3dB bandwidths of the two passbands are 2.1GHz and 1.5GHz,with the relative bandwidth of 17.8%and 9.0%,respectively.In addition,two bands are separated by two transmission zeros which leads to high selectivity,and its can be adjusted independently.The transmission coefficients on both sides of each pass-band will decrease 10dB/GHz.2.A novel second-order tri-band band-pass FSS is proposed,which is based on GSL(Gridded Square Loop,GSL)model by embedding two concentric Square rings in GSL(Gridded Square Loop,GSL).Three pass-bands operate in C-,X-,and Ku-band,respectively.The-3dB bandwidths of the three passbands are 3.0 GHz(4.8-7.8GHz),1.9GHz(10.1-12.0GHz)and 1.6GHz(13.6-15.2GHz),with the relative bandwidth of 31.31%,13.50%and 7.67%,respectively.The FSS has merits of high selective response,low insertion loss,and excellent angular stability.In addition,in each pass-band,there are two transmission poles which lead to flat band properties.Three bands are separated by two transmission zeros which leads to high selectivity,and its can be adjusted independently.The transmission coefficients on both sides of each pass-band will decrease 10dB in 1GHz range.Furthermore,the equivalent cicuit model is constructed to analysis the oprating mechanism of the FSS.At last,the FSS prototype was fabricated and tested.The measured rusults validate the feasibility of designing method.3.A high selectivity multi-band FSS is propsed.Based on the patch-apture-patch designing technique,we present a tri-band FSS with high selectivity by cascading three-layer structures.The middle layer is square grid array while the exterior two layers are composed of three square loops.The equivalent circuit model is adopeted to analysis the operating principle.Each passband contains two transmission poles which result in a flat and broad band response.Two adjacent bands are separated by two transmission zeros which leads to high selectivity.The transmission coefficients on both sides of each pass-band will decrease 10dB in 1GHz range.Three pass-bands operate in X-and K-band with the central frequencies of 8.4GHz,15.8GHz,and 19.88GHz,respectively.The-3dB bandwidths of the three passbands are 2.04GHz,1.72GHz and 1.16GHz,respectively.In addition,the FSS has merits of angular stability for both TE and TM polarizations under obique incient angles.4.Design of double stop-band FSS.To solve the problem in electromagnetic shielding,a shielding wall paper is proposed using dual-band-stop FSS which is composed compact improved four-legger loaded loop structure for wireless local area networks(WLAN)singal shielding.The central frequencies are working in 2.2GHz and 5.0GHz,respectively.The unit cell size is aboutλ/10.The profile is only λ/136.The-10dB bandwidth of the two bands are 280MHz and 300MHz,respectively.Furthermore,the shielding effectiveness(SE)is exceed over 20dB in wide incidence angle from -60° to 60°for both TE and TM polarizations.5.A novel multi-band FSS based on improved GSL unit cell is propsed,which aim to the application of 5G communication systems,one multi-band FSS is designed by cascading multilayer structures.The operating mechansium of proposed FSS is analysised using equivalent circuit model.The simulated results show that the proposed FSS has three transmission windows occure at the frequencies of 14.7GHz,27.7GHz and 43.1GHz,with the bandwidth of 13.9615.35GHz,24.69-30.70GHz,43.18-45.27GHz,respectively.