Study On The Composite Effect Of Plasma Sheath And Window Environment On Antenna Performance Of Near Space Vehicle

The aircraft will be wrapped by plasma sheath which is formed by high temperature ionization of the gas,when flying in the atmosphere at hypersonic speed.The electromagnetic wave can be strongly attenuated,reflected and refracted by plasma sheath apparent working frequency.It will affects the communication of aircraft,and even leads to the interruption of communication.The famous phenomenon is called communication blackout.So it is very important to mitigate or solve the communication blackout for the development of hypersonic vehicles.Antenna is the tool for external communication of hypersonic vehicles.The research on the performance of the antenna in blackout is helpful to solve the problem during blackout.The plasma sheath and the thermal insulation layer of antenna window are located in the near-field area of the antenna,and both of them have a great influence on the performance of the antenna.It has a strong guiding significance for the design of the hypersonic aircraft antenna to study the combined effects of plasma sheath and antenna window on the performance of the antenna.The main work of this paper includes:The effects of plasma frequency,collision frequency and thickness of homogeneous plasma on the transmission,reflection and absorption of the electromagnetic waves are studied firstly.The transmission coefficient,reflection coefficient and attenuation coefficient of electromagnetic waves with different polarizations are studied when they are incident into non-uniform plasma at different angles and frequencies based on the RAM-C? data.Secondly,the performance of the L~Ka band dipole antenna and circularly polarized patch antenna are studied when the plasma covered the antenna window based on the antenna window of an aircraft.And they are same to the different performance of the horn antenna and array antenna which are work in C~Ka band.It is found that the effects of the antenna window on different antennas are different.And the plasma-covered antenna window has different influence on the performance of the antenna working at different frequency.In general,the gain attenuation of the antenna is serious,while the working frequency is lower than plasma frequency.The attenuation is small when the working frequency is higher than plasma frequency.The plasma sheath on the aircraft antenna window is modeled and analyzed to study its influence on the antenna performance based on the data of plasma sheath formed by a hypersonic vehicle in a certain flight state.Finally,a sandwich method based on the structure of antenna window is proposed to mitigate the aircraft's blackout.The internal plasma,thermal insulation layer and outer plasma sheath can form a sandwich structure,when a thin plasma layer is generated inside the antenna window.A wave transmission window appears at a certain frequency while the electromagnetic wave penetrates the sandwich structure during the blackout period.The effects of plasma thickness,collision frequency and plasma frequency on the window frequency are discussed in detail.The results show that the plasma frequency of the internal plasma and the thickness of thermal insulation layer have a great influence on the window frequency.And the outer plasma has a small influence on the window frequency of the method.The simulation model constructed by horn antenna is used to verify the feasibility of the method.