Research And Design Of The Wideband Tunable Frequency Selective Surface

Frequency Selective Surface(FSS)is an artificial electromagnetic structure with spatial filtering characteristics,which can meet the needs of electromagnetic wave transmission regulation through the design of different electromagnetic parameters.FSS in the microwave frequency band has been widely used in radomes,absorbers,polarizers and other devices,and plays an important role in radar,electronic countermeasures and communications.However,the continuous innovation of the application environment makes the electromagnetic system more and more complex,which requires the FSS to have tunable and multifunctional properties.Compared with traditional passive FSS,Active Frequency Selective Surface(AFSS)can realize dynamic adjustment of electromagnetic transmission characteristics,and can also be designed to be multi-functional,so it can adapt to complex working environment and has high performance.research value.This paper focuses on the regulation of electromagnetic waves by active frequency selective surfaces,and designs an active tunable and multifunctional frequency selective surface.The specific work is as follows:1.A wideband multilayer tunable AFSS based on varactor diodes is designed.Firstly,an FSS composed of typical I-shaped metal and strip-shaped metal strip-gate is proposed,and a varactor diode is embedded on the I-shaped metal patch of the FSS structure to form an AFSS.The broadband filtering function of AFSS is regulated by the voltage of the varactor diode: when no bias voltage(0V)is loaded,AFSS can achieve broadband filtering in the frequency range of 3.55-4.43GHz;when the bias voltage is loaded to-19 V,AFSS can achieve broadband filtering The operating passband of the AFSS is tuned to 4.43-5.53 GHz,and the operating frequency of the AFSS is continuously tunable with the change of the bias voltage.Furthermore,the working principle of the AFSS is analyzed by the equivalent circuit method and the field strength theory,and the experimental test is carried out by processing the samples.The simulation and experimental results are compared,and the broadband filtering characteristics and tunable performance of the AFSS are confirmed.2.A switchable AFSS with dual functions of filtering and polarization is designed using PIN diodes.PIN diodes are welded on the strip metal surface layer of the device to realize the function switching of AFSS.By controlling the ON and OFF states of the top and bottom PIN diodes at the same time,AFSS can realize dual function switching.When the top and bottom PIN diodes are OFF at the same time,the AFSS can achieve broadband filtering at frequencies of 3.22-3.75 GHz;when the PIN diodes are turned on at the same time,the AFSS can achieve transmission-type line-to-circular polarization conversion at18-28 GHz.Furthermore,the bifunctional properties of the device were analyzed by observing the surface current distribution.3.A dual-function tunable AFSS based on varactor diode and PIN diode is designed.The device consists of a dielectric substrate,an FSS metal patch layer,a varactor diode on the top layer of the metal patch,and a PIN diode on the bottom layer,and a simple bias network is designed to facilitate the function switching and frequency tuning of the AFSS.By controlling the OFF or ON state of the bottom PIN diode,the AFSS can realize the switching of filtering and absorbing functions;in addition,by adjusting the bias voltage of the top varactor diode,the AFSS can realize the continuous tunability of the frequency of the filtering mode and the absorbing mode.Furthermore,its equivalent circuit and surface current distribution are analyzed,and finally experimental tests are carried out.The dual-function switchable and frequency-tunable characteristics of AFSS are confirmed by comparing the simulation and experimental results.