Investigation On Stealth Technology Based On Electromagnetic Bandgap And Its Appilication To Antenna

Electromagnetic bandgap (EBG) is a novel metamaterial which has been used widely in microwave region to realize high performance antenna and microwave components. But the scattering characteristics of EBG is not in emphasis, and the researches on stealth technology of EBG especially antenna stealth is few. This thesis is focused on the application of EBG to the stealth technology.The numerical methods to analyze the EBG structure are introduced, different numerical method is chosen according to different needs, the FEM method is chosen to analyze the eigen electromagnetic modes and the FDTD is chosen to analyze the in-phase reflection characteristics. The basic principles of this two numerical methods are introduced and practical examples are given.The electromagnetic characteristic of mushroom-like EBG is researched deeply in this chapter. The mechanism of bandgap forming and in-phase reflection forming are given briefly, the research emphesis is the characteristics of mushroom-like EBG structures loaded with lumped resistors. The surface-wave propagation along the resistor loaded EBG surface is discussed using the equivalent parallel RLC circuit and then the bandgap property is analyzed using the periodically loaded transmission line model. The surface impedance of mushroom-like EBG can be modeled using LC equivalent circuit and the formulas are given. The reflection phase of EBG predicted well using equivalent model compared with the measured results. The relationship of surface wave bandgap and in-phase reflection is researched and the conclusion is verified by experiment results.The application of mushroom-like EBG on changing the scattering characteristics of planar structure is studied. There is 1800 difference between the reflection phase of perfect electric conductor (PEC) and perfect magnetic conductor (PMC). The scattering characteristics of the composite structure combined with PEC and PMC will change. At first, the scattering characteristics of simple composite structure is analysis, the monostatic RCS is simulated and compared with the measured results, the measured results show that the backscattering is reduced effectively,but it is sensitive with the polarization of incident wave. The chessboard like structure is proposed, the scattering characteristics of it are analyzed, and the factors influnced the RCS reduction of chessboard are phase difference and unit size. The broadband chessboard is proposed which is composed of different parameters EBG structure.The ultra-thin absorbing material based on the EBG is studied. The EBG has the in-phase reflection characteristic which can be used to design ultra-thin absorbing material, the design principle is the same with the Salisbury screen. The equivalent circuit model of the absorbing material is developed and the design method is given. The results show that the absorbing band of RAM is decided by the reflection phase of EBG in the range±600. The measured absorbing frequency band of RAM moved toward lower frequency than the simulated results, which attributes to the parasitic capacitance introduced by lumped resistors. The EBG patch loaded with slot will decrease the operating frequency of EBG, this method can decrease the absorbing band of RAM. Finally the RAM based on the square loops is proposed.The application of this ultra-thin RAM to antenna array is studied finally. When the RAM is used to antenna, the structural scatter of antenna is reduced effictively and the radiation performance is maintained. The applications of RAM to ridged waveguide slot antenna array and helical antenna array show that the RCS of antenna is reduced and only gain decreased 0.9dB. This provides a new direction for antenna RCS reduction.