Research And Implementation Of Active Frequency Selective Absorptive Surface

With the rapid development of electronic reconnaissance,radar detection and other technologies,the combat positions of the warring parties and the high value targets of land,sea,air and sky are facing severe survival challenges,and they have raised higher and higher requirements for comprehensive electronic defense.Urgent,so it is particularly important to vigorously develop radar stealth and other technologies to improve the survivability of important targets and important areas.Conventional stealth shape technology and stealth material technology will deteriorate the performance of the target structure or affect the radar communication function.In contrast,as a spatial filter,the frequency selective surface(FSS)has a unique advantage.By using a unique structure,it realizes the bandpass or bandstop function in different frequency bands.For example,it can be used in a radome to obtain in-band stealth radome with transparent wave and external reflection function.However,this FSS stealth radome will generate reflected waves in other directions,so it is only effective for monostatic radar cross section(RCS)detection system.In addition,the traditional FSS stealth radome is not flexible enough to adjust dynamically,and it is difficult to adapt to the complex and changing electromagnetic environment.Against this background,frequency selective absorptive surface(FSAS)stealth radome technology and active frequency selective surface(AFSS)technology have gradually become research hot spots in recent years.The former realizes the function of out-of-band wave absorption by loading resistive elements on its surface,and through reasonable design,it can ensure communication within its working frequency band.In the latter,by adding active devices on the surface of the traditional FSS and controlling the external excitation of the active devices,the working frequency of the FSS can be tuned and the working state can be switched.This paper focuses on the following aspects of research work on the above FSAS technology and AFSS technology:1.A high-frequency transmission/low-frequency absorption FSAS structure is designed.Firstly,the basic theory of FSAS is carried out.Based on the basic equivalent circuit model(ECM),the relationship between transmission/reflection coefficient and impedance is derived,and the design principles of the absorption band and pass band of FSAS structures are analyzed.Then based on this,an ECM that meets the conditions is proposed.In the corresponding simulation model,the lossy layer realizes parallel resonance by inserting two lumped resistors into the metal cross-type patch and dividing it into two symmetrical parts.The bandpass layer is realized by the lossless slot FSS.The simulation results show that the structure realizes the-10dB absorption band of 4.8GHz to 11.2GHz,and at the time,the pass band with insertion loss of 0.7dB is realized in 12.75GHz.After that,the reduction characteristics of bistatic RCS and the influence of geometric parameters on its resonance characteristics of the above structure are analyzed.Finally,the sample is fabricated,and the experimental results agree well with the simulation results.2.A miniaturized dual-polarized FSAS structure with a transmission window in the absorption band is designed.First,the design method for realizing the transmission window in the absorption band is studied and an ECM that meets the conditions is proposed.The resonance frequency of the ECM is solved by a numerical method.In the corresponding simulation model,the resistive layer and the bandpass layer of the double-layer FSAS structure are composed of a lossy metal three-legged loaded element(TLLE)and a lossless square ring bandpass FSS.The simulation results of the model and its ECM are basically consistent.Afterwards,the characteristics of the bistatic RCS reduction of the above FSAS structure and the current distribution on the surface of the TLLE of resistive layer are simulated and analyzed.On this basis,in order to avoid grating lobes in the absorption band during oblique incidence of this structure,it has been miniaturized and improved.The resistive layer is folded by strips to reduce the size of the unit cell,and the bandpass FSS is replaced by the Jerusalem bandpass FSS with a more compact structure.The simulation results confirm that the stability of the frequency response from angular incidence of the miniaturized structure is improved.Finally,the sample was tested.The results show that under TE polarization,the pass band with insertion loss of 0.73dB is realized in 4.32GHz,the-10dB absorption band is from 2.65GHz to 7.9GHz.Under TM polarisation,the pass band with insertion loss of 0.71dB is realized in 4.34GHz,the-10dB absorption band is from 2.73GHz to 8GHz,which agree well with the simulation results.3.A polarisation-insensitive AFSS structure with switchable single/dual stopband is designed.Since most of the current research on AFSS is focused on the research of switchable frequency response characteristics and tunable resonance frequency,an AFSS structure with switchable number of stopbands is proposed.A double concentric ring(DCR)structure with good symmetry is used as the basis of the design,PIN diodes are loaded on the outer ring of the double ring structure,and the number of stop bands is switched by controlling the bias voltage of the diode.In the ON state,the structure forms two transmission zeros at 3.96GHz and 7.5GHz.In the OFF state,only one transmission zero is formed at 7.88GHz,and ECM is introduced to explain its internal working mechanism.Due to the quadruple symmetry of the structure,it exhibits very good polarization insensitivity and good stability of incident angle frequency response.Finally,the sample is fabricated by using the fusion bias network technology and tested by using the free space method,the results agree well with the simulation results.