Reserch Of Frequency Selective Surface In Ceramic Material

The radome is one of the key components in aircraft, not only to ensure the normalwork of the radar system, protect it from being affected by the harsh environment, butalso is the important factor to the performance of stealth of aircraft, so the radometechnology is important to design and manufacture of aircraft. This project has tworesearch topics: On the one hand, the effect of frequency selective surface（FSS） inradome to stealthy of aircraft is researched, the research method of FSS is summarized,three kinds of FSS model work in10GHz is designed. On the other hand, the fusedsilica ceramics with low dielectric constant is researched, include the theory of phasetransformation of quartz crystal and manufacture method. Finally, get the ceramicradome materials with good mechanical properties and dielectric properties by doping.First, the basic theory and analysis methods of FSS are summarized, and the onemedium loaded Y-shaped FSS model is designed. The influences of arm length, armwidth, dielectric thickness, incidence angle, incidence wave polarization of the FSS onfrequency response characteristic are simulated by CST, The results show that the centerresonant frequenciey of FSS is10GHz,and-3dB bandwidth is1.6GHz. It has very goodangle and polarization stability within the±40°range, so the FSS has very good filteringcharacteristics. Then, a kind of Three medium loaded Y-shaped FSS model working in10GHz is designed, it has wider bandwide, flatter passband, and angle and polarizationstability. A kind of unit which has a tortuous inner ring also is proposed, it is stable fordifferent angle and polarization, and could be work in different frequency if it isimproved. Its sample is manufactured, and the test result is same as simulation result.Second, the phase transformation of quartz crystal and the sintering process areresearched. It is found that dielectric constants of quartz ceramics increases with the riseof temperature, The minimum dielectric loss is4.1×10^-3at1175℃, but the maximumbending strength is just15.5MPa. Then nano SiO₂, Si₃N₄and Li₂O-K₂O-Al₂O₃arerespectively doped. The results show that nano SiO₂could reduce the dielectric loss,improve the material sintering density and bending strength. Si₃N₄would becomeamorphous silicon at high temperature so that it could suppress the crystal phase in the sintering process, but it also increase the dielectric constants and loss. The samplewhich doped Li₂O-K₂O-Al₂O₃almost melt into glass state at1300℃, and its bendingstrength reached163.65MPa, has greatly improved. Its dielectric constant is stablebetween5.5to6, and minimum dielectric loss is4.15×10^-3, so the doping ofLi₂O-K₂O-Al₂O₃is the most potential improvement program.