Research On Reconfigurable Frequency Selective Surface

The frequency selective surface is a periodic structure arranged in one or two dimensions.Due to its frequency selective characteristics,it can also be regarded as a spatial filter.In recent years,frequency selective surfaces have been widely used in satellite communications,radar stealth,electromagnetic compatibility and many other fields.The traditional frequency selection surface cannot change the transmission characteristics because it is designed and manufactured,so it cannot adapt well to the surrounding complex electromagnetic environment,and has certain limitations in application.Compared with traditional frequency selective surfaces,reconfigurable frequency selective surfaces can cope with changes in the electromagnetic environment and have advantages in practical applications.It is one of the important development directions of frequency selective surfaces in the future.This thesis will focus on this topic and conduct a series of studies on reconfigurable frequency selective surfaces.The related theories of frequency selective surfaces are studied first.The basic theories,several classifications,related technical indicators,characteristic parameters,vector research methods,scalar research methods,and design methods of frequency selective surfaces are introduced,and the frequency selective surfaces are theoretically studied in depth.The reconfigurable frequency selection surfaces based on active components are studied.First,a multi-functional reconfigurable frequency selection surface based on PIN diodes is designed.Due to the switching characteristics of PIN diodes,when the PIN diodes are loaded on the frequency selection surface,the forward and reverse bias voltages are applied to the PIN diodes.The frequency selection surface can not only show band-pass transmission characteristics or band-stop transmission characteristics in a specific frequency band,but also achieve band-pass transmission characteristics in different frequency bands.In addition,a reconfigurable frequency selection surface based on the varactor diode is designed.Since the capacitance of the varactor diode can vary with the bias voltage,when different bias voltages are applied to both sides of the varactor diode,the frequency Tuning can be achieved by selecting the center frequency of the passband of the surface.The reconfigurable frequency selection surface based on the adjustable structure is studied.First,a reconfigurable frequency selective surface based on liquid metal is designed.As a new material,liquid metal has also been widely used in recent years.Due to the fluidity of liquid metal,when it flows into different microchannels,the frequency selective surface can exhibit four transmission characteristics: all-pass,high-pass,low-pass and band-pass.In addition,a three-dimensional reconfigurable frequency selection surface based on a retractable structure is designed,and a metal cylindrical retractable structure is introduced between the dielectric layers.By changing the length of the structure,not only can the resonant center frequency be tuned,but also the transmission characteristic change from bandpass to bandstop.In addition,the polarization switching frequency selection surface is also studied.First,a linear polarization conversion frequency selection surface is designed.The incident horizontal polarization(vertical polarization)electromagnetic wave can be transformed into a vertical polarization(horizontal polarization)electromagnetic wave orthogonal to it through this structure.In addition,a circular polarization conversion frequency selection surface is designed,and the incident left-handed(right-handed)circularly polarized electromagnetic wave can be transformed into the opposite right-handed(left-handed)circularly polarized electromagnetic wave through this structure.