| Hypersonic aircraft resists external impacts of the plasma sheath generated by ionized air generated by its drastic friction against the aircraft and heat accumulation.Such impacts include thermal radiation that damages internal components and intense disturbance on the propagation of electromagnetic waves that causes misdirection,attenuation as well as aberration of signal,which contribute to severe interference on communication like communication blackout in all.Seeking a way to tackle external impacts,antenna window consists of thick thermal protection and insulation materials is applied to protect antennas,while serving as an obstacle of propagation itself.Considering these practical problems,contents that target on optimizing transmission performances of antenna windows coated by plasma sheath via various usage of periodic structures are proposed,and following research targets are achieved.Firstly,simulation models of an antenna window of partial hypersonic aircraft and layers of plasma sheath are constructed based on statistics of former projects like the RAM-C II program etc,influences on antennas caused by the presence of antenna window and plasma sheath of various body frequency are also analyzed and compared.Secondly,different types of Frequency Selective Surfaces(FSS)units are designed via Floquet theory and Fabry-Perot Resonator applications,researches are also carried out on which to determine connections between their parameters of size and performances,as well as optimization on antenna window via FSS arrays of various scale and distance.Fruitful simulations with different preconditions that vary from types of antenna,types of FSS,different scale of FSS array,ranges of frequency and presence of plasma sheath are executed and analyzed to determine how all the factors mentioned above influence antenna window,so that the feasibility of optimizing the transmission performance of antenna window via usage of FSS can be validated,and to which extent FSS arrays contribute to the optimization can be valued.On the very basis of these research,the effect of a newly proposed purely metallic FSS on transmission performance of antenna window,and the feasibility of applying a different design of antenna window structure are also discussed.Lastly,basing on a specific feature of interlayers consist alternate mediums of positive and negative relative permittivity that shows high transmission and low reflection performance on a specific frequency range,which is known as transmission window frequency,this article designs a calculation program so as to reveal further connection between parameter like relative permittivity as well as height of interlayers and feature like frequency range and band width of transmission window frequency.Since the reliability of this very feature is validated,this article applies a kind of meta-material unit with different size,and using parameter extraction method to determine the specific feature of meta-material structure that showing negative relative permittivity in specific frequency ranges,so the combination of meta-material structure,thermal protection and insulation material as well as plasma sheath fit interlayers that transmission performance of antenna window can be optimized via transmission window frequency.Therefore,simulation of meta-material unit based on periodic boundary condition and simulation of the entity of meta-material structure,antenna and antenna window based on radiation boundary condition are both applied to validate the feasibility that transmission window frequency can be generated via interlayers including metamaterial structure,the effects transmission window frequency exerted on optimization of the transmission performance of antenna window as well as reliability of determine transmission window frequency by rapid simulation analysis based on periodic boundary condition.These researches in all serve as possible methods of optimizing transmission performance of antenna window coated by plasma sheath when frequency of communication is lower than body frequency of plasma. |
