Research On Frequency-Selective Surface With Broad Stop Band With Optical Transparency

Frequency selective surface(FSS)is widely used in modern antennas and microwave communication systems due to the selective transmission of electromagnetic waves with different operating frequencies,polarization states and incident angles.The arrival of 5G provides greater interconnectivity between end users and infrastructure,but it also poses a challenge to entities that emphasize security.In order to maintain optical transparency while shielding unwanted signals when FSS is embedded in the glass of a building,and to ensure safe communication within the building,this thesis systematically investigates the design,analysis,processing,and measurement of band-resistive FSS structures based on optically transparent conductive Indium Tin Oxide(ITO)films as follows:(1)The basic characteristic parameters of the transparent conductive film are analyzed and measured.First,we compare the characteristics of each type of transparent conductive film,and select Indium Tin Oxide(ITO)transparent conductive film based on polyester resin(Polyethylene terephthalate,PET)as the material for this design.The space method is used to measure the square resistance of the ITO-PET conductive film in a wide frequency band(1-16GHz),and compared with the square resistance value given by the manufacturer.The results show that the ITO-PET transparent conductive film used in this design has stable and reliable nominal values.At the same time,due to the large surface resistance of the surface of the transparent conductive film,certain transmission attenuation will occur.(2)Based on the ITO-PET conductive film,a wide stop band FSS with transparent characteristics is designed.First,the aperture FSS is used as a design prototype to deeply analyze the current and electric field distributions at resonant frequencies and to establish an initial equivalent circuit model for the aperture FSS.Subsequently,this initial equivalent circuit model is analyzed and improved to achieve a wide-band rejection filter response,and the structural design of the band rejection FSS is carried out accordingly.During the design process,the link between the equivalent circuit parameters and the FSS structural parameters is accurately established based on the curve-fitting method.(3)Process and measure wide band FSS with transparent characteristics.Firstly,by comparing the process flow and technical requirements of various thin film etching techniques,the laser etching technique,which is a mature and efficient dry process,is selected to process the designed wide band FSS,and the specific process steps are explained.Subsequently,the spatial scattering parameter measurement method is used to test the processed samples,and the measurement procedure as well as the calibration of the data are given in detail.Finally,the measurement results are analyzed and evaluated systematically: the band-stop filter response is realized at 1.75 GHz,the relative bandwidth(-3 d B)is 373.54%,and the in-band loss is 1.5 dB.