Research And Design Of Broadband Electronically Control Frequency Selective Surface

Active Frequency Selective Surface(AFSS)consists of the traditional passive frequency selective surface and the active electronic control unit.The operating frequency,pass and resistance characteristics of device can be electrically tuned according to actual needs,powered by the power supply.Compared with the passive frequency selective surface,AFSS is more adaptable to the increasingly complex electromagnetic environment.Therefore,AFSS has received extensive attention in the fields of radar and aircraft stealth,high-power microwave weapon protection and electromagnetic compatibility.Currently,research on AFSS is mostly focused on achieving tunability of its operating frequency band.Although there are various ways to achieve that,the broadbandization of tunable frequency bands is currently the main problem.In this paper,based on the traditional FSS theory,by adding switch-type diodes,two working states of “transmission” and “shielding” are realized under a wide operating frequency range.At the same time,the AFSS has good stability in different polarization conditions and oblique incidence angles of incident waves.Finally,two wideband switching-type electronic control frequency selection surfaces were designed.First of all,after analyzing a large number of literatures based on different active devices such as diodes,MEMS switches,liquid crystal materials,and graphene,this paper compared the differences among various active components,taking into account the technical specifications of this article and selected the PIN diode as the active part of the proposed AFSS active devices.Then,starting from the working mechanism of traditional passive frequency selective surface,the fundamental theories such as Floquet theorem are introduced,and the two AFSS analysis methods of equivalent circuit model and transmission matrix method are used.Combined with the working principle of PIN diode,the design ideas and methods of AFSS is summarized and laid the theoretical foundation for the paper.Secondly,this paper selects the PIN diode as the active loading part and proposes two different design schemes for wideband electronic control frequency selection surface.The first scheme adopts a coupling unit structure,which makes the PIN diode's conduction to high-frequency signals destroy the resonant mode of the original broadband band-pass frequency selective surface and obtain a broadband “shielding” effect;the second scheme uses a two-wire transmission line.Instead of the traditional multi-layer frequency selection coupling between the surface layer and the layer,a PIN diode is used to control the on and off of the two-wire transmission line,which in turn controls the overall filtering performance of the AFSS.Finally,the two schemes are analyzed by the equivalent circuit method and the transmission matrix method respectively,and the relevant parameters in the equivalent circuit model are extracted,which provide the theoretical basis and guidance for the design and optimization of the structures.The operating bandwidth of the "transmission" state is 8-14 GHz,the bandwidth of "shielded" state is 2-18 GHz,and it has good polarization stability and oblique incident stability,with a maximum oblique incidence angle of 30°.