Research And Design Of High Performance Frequency Selective Surface

The Frequency Selective Surface has unique spatial filtering characteristic and it has important application value in the electromagnetic field.The design of the high-performance FSS is always the unremitting pursuit of researchers.This article focuses on the research hotspots of FSS in recent years,including multi-layer cascaded FSS,active reconfigurable FSS and conformal FSS.Two designs of FSS with excellent transmission characteristics are introduced.The main contributions of this thesis can be summarized as follows:First.The conception and working mechanics of FSS are introduced.The reasons of the occurrence of grating lobes are discussed and the conditions for avoiding the generation of grating lobes are deduced.The numerical analysis methods such as the mode expansion method and the spectral domain method are elaborated in detail.The general design ideas for FSS are discussed.Taking the classic ring gap FSS as an example,the common factors that affect the transmission characteristics of FSS are analyzed in detail.It gets a certain conclusion which have realistic directive significance in FSS designs.Second.A new design of ultra-wide band(UWB)FSS is proposed.The UWB FSS has always been a hotspot in FSS research area.The use of multi-layer cascaded structure makes the FSS present broadband or even UWB characteristics,which has important practical value.For a long time,most researches and designs of band-pass UWB FSSs focus on the X-band and higher bands.The majority of the FSS that work in the S-band,L-band or even lower band are conducted on electromagnetic wave transmission ability within the operating frequency range,but the transmission bandwidth is narrow.In addition,it is very rare to realize a UWB FSS design with excellent sideband drop characteristics and out-of-band reflection characteristics.For this purpose,we present a new design of UWB band-pass FSS.The FSS works in P,L and S bands and has a bandwidth of 0.52 GHz to 3.81 GHz with the relative bandwidth of 152%.It has excellent miniaturization characteristics with the periodicity smaller than 0.026?(where ? represents the wavelength at lower frequency of the passband).The sideband drop performance is excellent,reducing from-3d B to-57 d B in 0.15 GHz.In addition,it also has broadband out-of-band reflection characteristics,and its transmission coefficients are basically less than-14 dB in 3.86GHz~7.81 GHz.We describe the design process of the UWB FSS in detail.Its equivalent circuit is given and the circuit simulation results is compared with the HFSS simulation results.The prototype of the UWB FSS is manufactured and measured in an anechoic chamber.The ultra-wideband band-pass FSS performs well in all aspects,providing a new idea for the design of UWB FSS.Third.A design of electrically controlled FSS radome is presented.Compared to classic passive FSSs,the resonance characteristics of the reconfigurable FSS can be changed.Reconfigurable FSSs can adapt to the changes in the external electromagnetic environment and overcome the shortcomings of traditional FSSs.In practical applications,many devices are not planar structure,so conformal FSSs are needed in some areas.It has important significance to study conformal FSSs.Combining the reconfigurable technology with the conformal technology,we design an electrically controlled FSS radome.The FSS unit is diode-loaded and can change the resonant characteristics by controlling the on-off state of diodes.The FSS radome shows band-pass characteristics in generally and the antenna in it can work normally.When the electromagnetic waves in a certain direction will influence the antenna,the diodes in the corresponding area is turned on.In this time,this area will exhibit reflection characteristics,avoiding the negative influence to the antenna.The other areas are still showing transmission characteristics so the antenna can work normally in these areas.We elaborate the design process of the basic unit of the FSS radome,and introduce the method of how to model the FSS unit on the hemispherical surface.Taking the monopole antenna as an example,the performance of the electronically controlled FSS radome is analyzed.It is proved that this design is feasible.