Frequency Selective Surfaces In Spatial Domain Based On Equivalent Circuits

Frequency selective surfaces(FSS)are widely used in the field of electromagnetic microwave,thus they have been one of the hot topics in recent decades.As one of the most effective methods to design and analyze FSSs,equivalent circuits attract many scholars.Although related research in this area is relatively mature,most of the FSSs are applied in frequency domain,and so as the corresponding equivalent circuit models.There are relatively few studies on the FSSs in the spatial domain or angular domain.The concept of spatial filters is proposed early;however,no one has systematically defined the concept of spatial frequency yet.This thesis summarizes some existing problems and defects on the basis of researches on FSSs in domestic and foreign relevant literatures and its development trend.The main research points and innovations of this thesis are as follows:1)The concept of spatial frequency is proposed and defined first.By the analysis method of field-circuit combination and the equivalent circuits of two-port network,the physical models are equivalent to shunt or cascaded elements to construct an equivalent circuit that accurately describe the response in a certain bandwidth.After establishing the precise correspondence between the physical structure and the equivalent circuit elements,the structure of FSSs can be obtained in turn through the equivalent circuit,greatly improving the design efficiency of FSSs.2)Based on the proposed spatial frequency,the equivalent circuit in the frequency domain is improved,and the equivalent circuit of FSSs in the spatial domain is proposed,so that FSSs can be easily and intuitively expressed in the spatial domain or angular domain,that is,the characteristic response at different incident angles.3)Through the concept of spatial frequency and the equivalent circuit model extracted above,the foundation of the spatial filter,J/K converter in spatial domain,is proposed,and the detailed theoretical calculation and simulation extraction methods are given.A spatial FSS with low-pass characteristics are designed by the synthesis of J/K converters.The specific design method is given systematically and in detail.4)The even-odd mode analysis is further applied to the design of FSSs.A frequency selective surface with dual-band polarization diversity is proposed based on the equivalence of the U-shape unit resonance.Coupling theory is introduced to analyze the polarization diversities at different frequencies.This FSS can be used in a reflectarray to achieve the isolation of transmitting and receiving.