Study On Optimization Of The Performance Of Microwave Absorber

Beidou navigation system is a global satellite positioning and communication system developed by China.Because the distance between the navigation satellite and ground is very far,the signal reaching the ground terminal is extremely weak,so the signal is vulnerable to interfere.If there is a strong coupling between the terminal antenna array elements,the radiation pattern of the antenna will have serious distortion and it will influence on the reception of navigation signals,thus reducing the mutual coupling between the array elements becomes one of the important task for improving the performance of satellite navigation positioning terminal.With the development of meta-material,the latest meta-material absorbers provide a possibility to reduce the mutual coupling of antenna elements and improve the radiation characteristics of the antenna array.To this end,the main work of this paper is to study the ultra-thin sheet absorbers with high absorption and wide absorbing bandwidth in the B3 band of the Beidou navigation.The sheet absorbers are usually composed of three layers,in which the metal pattern is on the top layer,the medium substrate on the middle layer and metal short line or the ground floor on the bottom.In order to expand the bandwidth of the absorber,the traditional way is to add lumped elements,use multilayer absorbing materials or multi-unit array to increase the resonance point.But these methods are not applicable in the L band and cannot achieve the expected performance.In this paper,magnetic materials are introduced to achieve a wide bandwidth in low frequency.The main works are as follows:First the "sandwich" structure is used,and the medium substrate is high permeability material.Magnetic material causes the increase of magnetic loss and the dielectric constant of the material is high,the synergistic effect of high permeability and high dielectric constant makes the equivalent impedance of the material to match with space,periodic metal pattern on the surface will produce resonance affecting the entire work frequency band.By optimizing the absorber parameters will realize better absorbing performance in the specific frequency.The effect of the material and structure is discussed.Finally the absorber prototype is made and the performance is measured by the experiment.Secondly,on the basis of the introduction of magnetic material,the periodic structure of the surface is combined with metal material and resistance film.The substrate material is still using the same high permeability material.In order to achieve wider bandwidth,the composite structure with a square metal sheet and the resistance frequency selective surface is used as the periodic pattern on the surface.Through the resonant absorption of the metal sheet and the ohmic loss of frequency selective surface,it realizes the broadband absorbing performance in low frequency.Furthermore,the periodic metal pattern is loaded inside the magnetic material to realize the wide absorbing bandwidth.The material is still using the same high permeability material and the periodic metal pattern is embedded in magnetic material to form a composite material.The electric field distribution is changing along the thickness direction,resonance is introduced into the interior of the absorber.The interaction of the resonant loss,magnetic loss of magnetic material and electromagnetic interference in thickness direction can achieve good absorbing performance in a wide frequency range.Finally,two magnetic materials are used to interact with each other,and the periodic metal patterns are loaded on the surface of two different magnetic materials.The multi-layer absorbers can increase the resonant points and realize the wide-band absorption,and the two layers of magnetic materials can also interact with each other.Generally permeability and permittivity of the upper medium is smaller than the lower medium,the lower magnetic media still uses the same high permeability as before.The parameters of the upper magnetic material can be debugged to make the absorber achieving broadband and high absorption performance.However,the upper magnetic material having this parameter is not available.Using the available material cannot achieve the best results,but it can also realize a certain absorbing performance in the wide frequency range.In this paper,the bandwidth broadening of ultra-thin microwave absorbing sheet in the L band has been studied.Several methods are proposed to realize many absorbers with good performance,and the influence factors of the structure have also been discussed.