Bandpass Frequency Selective Surface With Wide Stopband Based On Stacked Slotline Structures

As a kind of spatial filter,frequency selective surface?FSS?is widely used in the field of antennas and microwaves,has selective filtering characteristic for electromagnetic wave with different frequencies,polarizations and incident angles.Traditional FSS is an infinitely large periodic array composed of two-dimensional planar element structures,and its design and processing are relatively simple.However the disadvantages of traditional FSS are large cell size and limited resonant modes.The new FSS based on a three-dimensional structure can excite multimode resonances,demonstrating high quality filter characteristics.The disadvantage of new FSS is that the unit structure is complex and difficult to implement.This thesis combines the advantages of two-dimensional FSS and three-dimensional FSS,designs a three-dimensional FSS based on stacked slotline structure.Meanwhile this thesis analyzes in depth the working mechanism and equivalent circuit model of this type of FSS,designs processes and tests two examples.Research results show that this type of FSS can achieve high filtering performance and reduce processing difficulty.The specific research contents are as follows:Firstly,this thesis briefly describes the research background,research status in recent years,some simple structure introductions,and the basic analysis methods of FSS.Particularly,we introduces the analysis mechanism of equivalent circuit model,and taking the metal patch FSS and the double square loop FSS as example,this thesis introduces the process of extract circuit parameters by empirical formula.Secondly,this thesis proposes a class of bandpass FSS with improved out-of-band rejection performance by using stacked slot line structure.The proposed FSS consists of a periodic array of slots etched in pieces of single-layer PCBs,which are vertically placed along the periodic plane and then stacked together with a certain distance.In order to better understand the operating principle of this type of FSS,design process of the stacked uniform-impedance slot line FSS?SUS-FSS?,the SUS-FSS loaded with inductor and stacked stepped-impedance slot FSS?SSS-FSS?with loaded strip is presented step by step.Thirdly,a single-polarized SSS-FSS and a dual-polarized SSS-FSS are designed based on stepped impedance slot line structure.The center frequencies of bandpass of the two structures are both around 3 GHz,and the out-of-band rejection(|S₂₁|?-20 dB)of single-polarized structure ranges from 4.3 GHz to 20.6 GHz,while dual-polarized structure can provide the upper rejection band from5.86 GHz to 14.9 GHz(|S₂₁|?-20 dB).Measured results indicate that the proposed FSS features simple topology in geometry,miniaturized unit-cell size,wide upper rejection band,and stable frequency filtering response under a large variation of incident angles.Lastly,in this thesis,a measurement and calibration method of scattering parameters is presented for FSS under non-ideal measurement environment.The proposed method can eliminate the influence of spatial signal attenuation,couplings between antennas,and multipath effects for the real measured results,thus leading to good agreement between the real measured results and the ideal measured results.This thesis takes the single-polarization SSS-FSS test process as an example,elaborates the measurement and calibration process,and obtains real scattering parameter test data.The method of measurement greatly reduces the strict environmental requirements of the FSS and other artificial periodic structures in the measurement process,and also reduces the measurement cost.