Research On Tunable Frequency Selective Surface Based On Liquid Crystal

The frequency selective surface(FSS)acts as a spatial filter and can exhibit total reflection or full transmission characteristics for electromagnetic waves of different frequencies.With a periodic metal slot cell cycle and metal patch cells,different characteristics such as bandpass and bandstop can be achieved.Tunable FSS Compared to the classical FSS,the resonant frequency can be changed as the external excitation is controlled.Therefore,the tunable FSS can better change the resonant characteristics in response to changes in the electromagnetic environment,thereby exerting its maximum effect.This article has conducted a series of studies on tunable FSS designs for this hot issue.First of all,this paper starts from the basic working mechanism of FSS,analyzes the theory of FSS filtering from the perspective of theory,introduces some basic characteristics of FSS,analyzes the key factors of FSS design,and gives practical design ideas.The basic theory includes the basic working principle of FSS,the factors affecting its performance,the grating lobes,and the analysis method of FSS.Then,the working mechanism of the dielectric anisotropy of the liquid crystal with voltage changes is studied,and a tuning method for changing the capacitance between the front and rear FSS layers by changing the voltage of the liquid crystal cell is designed by designing a capacitive junction where the liquid crystal cell is periodically located between the front and rear FSS metal layers.Three different FSS structures are designed by using this method.The first structure is based on the Jerusalem cross patch and metal grid network structure,and adds a metal narrow strip that facilitates feeding.The final simulation results show that the structure can achieve a continuous tuning ability of 5.2%.Based on the former structure,this paper designs two tunable FSSs with miniaturization characteristics.The first kind of miniaturized FSS is based on the complementary structure of the Jerusalem cross patch.The Jerusalem cross patch and the gap in Jerusalem are placed differently,which can effectively block the secondary resonant current path and achieve the purpose of suppressing the grating lobes.And this structure has the characteristics of miniaturization and large angleincident stability,which can achieve 13.1% continuous tuning.The second type of miniaturized FSS is a structure designed based on the principle of mutual coupling.With this structure,we can obtain a broadband tunable FSS.In addition,because of the type-coupled method,this wide-band FSS also has the characteristics of miniaturization and large-angle incident stability.On the basis of not affecting the original structure,lumped elements are added to facilitate feeding.Simulation results show that the structure has a bandwidth of 2 GHz and can achieve a continuous tuning capability of 13.2%.