| Missile radome is utilized to make aerial inside work safely under abominableenvironment, whose properties have great effect on missile's control and guideprecision. In order to enhance the disturbance resistance and develop theanti-radiation radome, the broadband transmission properties are necessary for theradome. Radome wall structure with broadband properties is mainly including thethin wall, sandwich wall and multilayer wall structure. Amoung these structures,sandwich structure including A-sandwich and B-sandwich structure is adaptable forthe flown line radome and can realize the high transmission in a broad frequency,thus, it is the structure investigated in this paper.Based on the requirement of radome, by using the electromagnetic wavetransmission and reflection theory, the calculation method of transmission efficiencyof sandwich structure is conducted when the frequency varied from 1 to 18GHz, thedielectric properties and structure (thickness) value are optimally designed. Theresults suggest that when the dielectric constant of the core layer is 2～2.5 and thesurface layer of 5～7, the thickness ratio between the surface and core layer is 1:15,the wall thickness is 6mm, the transmission efficiency is more than 90% when thefrequency is 1～4GHz and 9～15GHz.According to the design results, considering the mechanical and thermalproperties, the porous silica ceramics with low dielectric constant and zirconiumphosphate ceramic, Si-B-O-N system ceramics with high dielectric constant areselected in this paper.Using the dynamic gel-casting molding method, making the fusedsilica slurry, choosing the suitable sintering temperature, controlling thecontent of organic substance, the porous fused silica ceramics are prepared.Pore sealing technique is also studied and the effect of pore-sealing coatings on thedielectric properties is investigated as well. The results suggest that the bestconditions for the silica slurry is as follows: pH=4, the content of AMis1～5wt.%, the content of solicitation is 0.1wt.%, temperature is 60～80℃,the content of surface activation is 1.2wt.%. Porosity is well controlled by adjusting the content of organic substance. By adjucting the composition ofthe silica slurry and choosing the sintering temperature, porous silicaceramics with porosity of 5～33%, bending strength of 20～65MPa anddielectric constant of 2～3.4 are successfully obtained. The coating materialis prepared by using the sol-gel method and performs good water resistance,high temperature resistance and high wave transmission properties. Thecoating hardly influences the dielectric properties of porous silica ceramis.The fabrication process of zirconium phosphate powders and ceramics isstudied. The results suggest that, ZrP2O7 powders are stable existed before 1500℃.ZrP2O7 ceramics with density of 2.8～2.98g/cm3 are prepared by using MgO as thesintering additives at different sintering temperatures. When the sinteringtemperature is higher than 1250℃, the density hardly changes with the sinteringtemperature. The density and bending strength of ZrP2O7 ceramic firstly increasethen decrease with increasing the content of MgO. ZrP2O7 ceramic with dielectricconstant of 6～8.5 and dielectric loss tangent of less than 10×10-3 is obtained, whichis in agreement with the requirement for radome application.The Si-B-O-N system ceramics are prepared by gas pressure sintering (GPS)technique and adjusting the content of BN and nano SiO2 powders. The mechanicalproperties, thermal shock resistance, ablation resistance and dielectric properties areevaluated. The results suggest that by adding 5～30wt.% content of BN, the fracturetoughness, thermal shock resistance and dielectric properties are improved but therelative density and the bending strength decrease. By adding SiO2 nano powders,composites with higher relative density, bending strength and fracture toughness areobtained. When the content of BN is 20 wt.%, by adding 5wt.% SiO2 nano powders,Si3N4/BN/SiO2(n) composites with controlled dielectric constant of 4.3～5.9 areobtained. In all these cases, the dielectric loss is less than 10×10-3. The compositeshave better thermal shock resistance and their ablation rate is only 0.042mm/s.Then, the sandwich structure is realized by using phosphate binder method andeach layer is bonded with designed dielectric properties and thickness.ZrP2O7/SiO2/ZrP2O7 A-sandwich structure and SiO2/Si3N4-BN-SiO2(n)/SiO2B-sandwich structure radome material are prepared and the effect of binder on thedielectric properties is studied, the broadband properties is tested. The resultes suggest that the binder nearly has no effect on the dielectric properties of thecomposite. The binder is porous structure and has stable interface structure. Thetransmission efficiency for A-sandwich structure is more than 90% when thefrequency is 2～5GHz and 9～12GHz, while the transmission efficiency forB-sandwich structure is more than 90% when the frequency is 3～6GHz and11～17GHz, the test results are in agreement with the theoretical value.Using cold iso-static pressing and low stress machining technique, phosphatebinder method, each radome layer is precisely in agreement with the design size andthe wall thickness requirement. ZrP2O7/SiO2/ZrP2O7 A-sandwich radome andSiO2/Si3N4-BN-SiO2(n)/SiO2 B-sandwich radome are prepared and the broadbandproperties is tested. The results suggest that the transmission efficiency forA-sandwich radome is more than 90% when the frequency is 3～4GHz and 7～8GHz,while the transmission efficiency for B-sandwich radome is more than 90% whenthe frequency is 5～6GHz and 13～14GHz.
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