Design And Research Of Novel Radome Based On Multilayer Frequency Selective Absorber

With the rapid development of radar reconnaissance and detection technology,the traditional radome cannot achieve omni-directional stealth for target object.Therefore,the military fortresses and targets with strategic significance on both sides are facing more severe survival challenges.The Multifunctional Frequency Selection Absorber(MFFSA)is kind of a multilayer composite periodic structure,which can achieve both absorption characteristics and Lossless filtering characteristics during its working band.Generally,it can be carried out by cascading a lossy impedance surface layer and a lossless FSS layer,which can realize selective absorption or scattering for incident electromagnetic waves.Furthermore,by using the MFFSA,the object under the dome can still communicate with its own radar outside but with low radar cross section,which has a great value in the field of radar stealth.Based on the background above,a MFFSA with a single absorption band based on 2D periodical structure metal grid with loading resistance,and a MFFSA with dual-band absoption based on 2.5D metal grid unit with loading resistance are proposed,fabricated and measured in this paper,while the the details are as follows:Firstly,based on the theories of microwave network and the transmission lines,the equivalent circuit and its analysis method of cascading multi-layer FSS is derived and summarized.In this way,the free space and dielectric substrate can be seen as transmission lines,and the periodic structure of each layer is equivalent to the impedance loads connected in parallel to the transmission lines.Basd on the theories of microwave network,the relationship between the structure scattering coefficient and the equivalent impedance of the impedance surface layer is deduced.The impedance conditions of the impedance surface layer in the MFFSA structure to realize absorption and transmission in specific band are are analyzed.Moreover,we establish and verfiy the equivalent circuit model of MFFSAs with single-band absorption and multi-band absorption.Secondly,we propose a MFFSA structure which can achieve absoption at lower band and transmission at higher band.In this part,we derive the equivalent circuit model of the grid structure according to the filtering characteristics of the metal grid structure at the beggining,and then propose an impedance surface layer design by loading resistance on the metal grid structure.After that,the mechanism of the three-level gap coupling wideband bandpass FSS is analyzed theoretically,and a gap coupling wideband bandpass FSS with circular patch is designed.In the final,the impedance surface layer is connected to the band-pass FSS to constructure the MFFSA,which can realize absorption at lower frequency band and transmission at higher band.The simulation results show that the designed MFFSA structure has an absorption rate of more than 80% in the range of 3.40GHz-8.16 GHz,and its transmission band with an insertion loss of less than 1.25 d B is 9.02GHz-12.03 GHz.The sample is also fabricated and measured,while the experimental results agree well with the simulations.Thirdly,we proposed a wide-band absorption-reflection-absorption dual-band absorption MFFSA structure.In the beginning,the design method of the multi-band absorption MFFSA is studied.Based on the metal grid structure,a 2.5D resonant structure is introduced to realize the dual-band absorption by loading resistors on the metal structure.Simulation results show that the absorption frequency bands with the absorption rate greater than 80% are 3.08GHz-11.04 GHz and 15.65GHz-22.26 GHz,and the fractional bandwidth is 113.6% and 34.9%,respectively.To verify our proposal,a sample is also fabricated and measured.However,there is a problem during the processing of the impedance surface layer,which is that the two impedance surface layers are not fully adhered,therefore extra resonances occurred and results in a little difference between simluations and measurements.