Design And Applications Investigation Of Multifunctional Broadband Active Microwave Absorber/Reflector

The development of radar detection technology is a greater challenge for high-value ground targets to achieve camouflage and stealth.Using the multifunctional absorber/reflector to control electromagnetic signature is an important way to realize the camouflage and stealth of high-value targets on the ground.And the continuous expansion of the radar frequency range puts higher demands on the bandwidth performance of the absorber/reflector.Based on the Active Frequency Selective Surface(AFSS),this research aims to realize the design of multifunctional broadband absorber/reflector and simulate its applications.The model of periodic array of the absorber/reflector and its impedance tuning technology was carried out,and the restriction mechanism of the parasitic parametric effect of active microwave devices on the bandwidth performance and its suppression strategy were proposed.The broadband frequency tuned absorber/reflector and the broadband amplitude switchable absorber/reflector were designed respectively.Moreover,the scattering characteristics of the tank model which was loaded the switchable screen structure were simulated and analyzed.The main research results and innovations obtained are as follows:Firstly,aiming at the problem of limited working frequency bandwidth caused by the parasitic parameter effect of active devices in the absorber/reflector design,the model analysis and equivalent circuit model simplification of varactor diodes and PIN diodes were carried out.The values of each parameter of equivalent circuit model under different bias states were determined respectively.Combined with the equivalent circuit analysis method of the absorber/reflector structure,the bandwidth limiting effect of the parasitic effect of the microwave active device on the microwave reflectivity of the absorber/reflector structure was revealed in details.Based on the large resistance parallel suppression and LC parallel resonance cancellation,the suppression strategy of parasitic parameters in varactor diodes and PIN diodes was further proposed.Finally,the working bandwidth of absorber/reflector is extended from C band(4.0 ～ 8.0 GHz)to C/X band(4.0 ～ 12.0 GHz).This breaks the technical bottleneck of bandwidth limitation caused by parasitic parameter effect of device in the absorber/reflector and it provides a new way for the design of broadband absorber/reflector applications.Secondly,focusing on the absorber/reflector structure impedance control technology,a design strategy is proposed for adjusting the imaginary part of the impedance to achieve frequency tuning and adjusting the real part of the impedance to achieve amplitude control.Based on the simulation model of the absorber/reflector structure,the mechanism of impedance switching control of absorber/reflector was exmined by combing transmission line theory with equivalent circuit method.The dynamic change law of the impedance of the absorber/reflector was clarified.Hence,as the adjustment of the impedance of the AFSS layer makes the overall impedance of the structure match the air impedance,it appears in an absorbing state,and while it is completely mismatched,it appears in a reflective state.A low frequency polarization insensitive frequency tuning absorber/reflector with the working bandwidth over a range of frequencies 1.0 ～ 2.0 GHz was developed by using the varactor diodes,combined with the law of virtual part by way of the impedance of the equivalent circuit analysis and the suppression strategy for the parasitic parameters of the varactor diode.A wideband amplitude-regulated absorber/reflector with the working frequency bandwidth of 3.9 ～9.8 GHz is developed by using the PIN diodes,combined with the change rule of the real part of the equivalent circuit impedance analysis and the suppression strategy of the parasitic parameters for PIN diodes.The microwave reflectivity control technology based on absorber/reflector provides a new strategy for enhancing the camouflage and stealth performance of high-value targets.Finally,in order to balance and compatible the electromagnetic scattering characteristics between high-value targets and environments,a solution to load a broadband amplitudemodulated switching screen for targets was proposed,which combines the switching characteristics of the absorber/reflector.Taking a metal tank as the examples of practical applications,the main source of electromagnetic scattering was analyzed when the electromagnetic wave was normal incident,and the strategy of decomposing the complex model into a simple target was put forward.The electromagnetic scattering characteristics of typical flat structures and cylindrical surface structures were both simulated and analyzed.The electromagnetic switching characteristics after loading the switchable screen were also simulated and analyzed.According to the scattering controlling requirements of the tank model,a broadband low-angle oblique incidence polarization-stable and amplitude-adjustable absorber/reflector which was suitable over a range of frequencies 3.9 ～ 11.0 GHz was developed.According to the electromagnetic background characteristics of different environments,thus,Radar Cross Section Reduction was proposed to evaluate whether the electromagnetic characteristics of target were in consistent with background environment or not.The simulation results and the imaging of the metal tank loading switchable screen in a specific environment showed that the designed absorber/reflector had the ability to regulate the electromagnetic characteristics of the metal tank model.And it can realize the compatibility of the tank model with the electromagnetic scattering characteristics in a specific environment.Therefore,a new operational scheme was provided for the balance and compatibility of electromagnetic characteristics between targets and complex environments in radar countermeasures,and a new mode of camouflage and stealth of high-value targets was constructed.