Analysis And Optimal Design Of Microwave Absorption Properties For Frequency Selective Surfaces Using Graphical Methods

The adjustable electromagnetic absorbing structure has made considerable progress in the last years. In particular, attention is paid to the lossy frequency selective suface (FSS) to chose it one of candidate systems to realize broadband wave absorbing structure. At first the graphical method for analysis and optimization design of broadband wave absorbing structure is presented. The graphical method is employed to analyse the electromegnetic properties and absorbing principle of Salisbury screen and Jaumann absorber. And then a single and double layer optimal broadband impedance match model based on the single resonance FSSs has been established for the design of broadband wave absorbing structure. Futhermore. the absorbing principle of smart absorbing materials based on active FSSs have been extensively analysised by graphical method for analysis and optimization design of smart absorbing structure.The principles of the Salisbury screen and the influences of the structure parameters to the wave absorbing performance has been studied by Smith chart method and equivalent circuit method. The results indicated that the thickness of the Salisbury screen could be adjusted by the permittivity of the dielectric substrates. If the permittivity of the dielectric substrates increased, the thickness of the Salisbury screen would decrease and the absorption peak would narrow, the bandwidth would decrease.The Jaumann absorber was analysised by Smith chart method and equivalent circuit method. The results revealed that the Jaumann absorber could be designed to produce a larger bandwidth, particularly as more layers were added. A further compression of the final curve was seen because more layers were added. The Jaumann absorber allow obtaining remarkable performance (-8dB in the band from4GHz to16GHz) with an overall thickness of10mm. This performance is superior to Salisbury screen with the same thickness.A single layer broadband electromagnetic absorbers using square loop and circular loop shaped FSSs were designed by Smith chart method and equivalent circuit method. The impedance match law was found as follows:When the null center frequency susceptance of the ground plane is nearly equal to the resonance of the FSSs; resonance conductance of the FSSs remain within a fairly reasonable range; the endpoint frequency susceptance of the FSSs is nearly equal to the susceptance of the ground dielectric plane, the susceptance of the FSSs and the ground dielectric plane to a large degree cancel each other leading to a small reflection. The single layer absorber allow obtaining remarkable performance (-8dB in the band from4GHz to18GHz) with an overall thickness of5mm. This performance is superior to Salisbury screen, optimized Jaumann screen and the available commercially non-magnetic single layer structures with the same thickness.For the double layer broadband electromagnetic absorbers using square loop and circular loop shaped FSSs, the impedance match law was found as follows; When the null center frequency susceptance of the ground plane is nearly equal to the resonance of the two sets of FSSs; resonance conductance of the up-down layer FSSs remain within a fairly reasonable range;The process curve transform through the up layer dielectric slab and obtain the next curve near the admittance curve of the up FSSs. The final match between the curve and admittance of the up layer FSSs yeilding to a broadband absorbing property. The double layer absorber allow obtaining remarkable performance (-8dB in the band greater than3.3GHz) with an overall thickness of10mm. This performance is superior to Salisbury screen, optimized Jaumann screen and the available commercially non-magnetic double layer structures with the same thickness.The research indicated that the smart absorbing materials could be designed by loading the active FSSs. A tunable absorbers comprised of a new combination shaped FSSs printed on a dielectric substrate loaded with PIN diodes were demonstrated. Through at different voltages to control the diodes, the reflectivity characteristics of the structure can be varied. A qualitative analysis by the equivalent circuit method is carried out on the parameters of the tunable absorbers. Though the impedance match, the structure can be turned to provide a variable reflectivity response over a band of frequencies from2GHz to18GHz.