Study On The Propagation And Scattering Characteristics Of Electromagnetic Waves In Inhomogeneous Plasma

The interaction between electromagnetic waves and inhomogeneous plasma has application prospect in VLF(Very Low Frequency)navigation,RCS(Radar Cross Section)calculation,and ionospheric radio wave transmission.For example,the positioning accuracy of VLF global navigation system Omega depends mainly on the phase calibration of the ionosphere's influence on the propagation of radio waves.Satellite-to-earth communications may be impacted by Electrical propulsion plumes,while the RCS of targets have been impacted significantly by rocket tail flames on in low-band frequency.Therefore,studying the interaction between electromagnetic waves and inhomogeneous plasma has important reference significance in target detection and identification,satellite communication and so on.In this paper,we study the propagation and radiation of VLF waves in the ionospheric background,the interaction between aircraft plumes and electromagnetic waves,the transmission of electromagnetic waves in plasma and the electromagnetic scattering of inhomogeneous plasma.The main work and innovations are as follows:1.The full-wave analytical expression of the electromagnetic field distribution in the ground-ionospheric waveguide is given when the radiation source is located in the atmosphere.The basis of the full wave method is the propagation matrix method and plane wave expansion,which is generally used for the analysis of radiation problems in layered media.Then radiation field in space domain is represented as integral in the wave number domain.By integrating in the vertical wave number domain,the radiation can be represented as a superposition of plane waves with different directions.If the atmosphere and ionosphere are regarded as layered media,the vertical wavenumber integral contains first-order singularities when the radiation source is located in the ionosphere,which is relatively easy to handle.When the radiation source is located in the air,the vertical wavenumber integral contains second-order singularities,which is more complicated.Therefore,there are few full wave method documents on research of radiation characteristics in the air and ionosphere when VLF source located in the air.In this paper,the air is considered as an isotropic medium with micro-conductivity,the vertical wave number integral that has second-order singularities is solved,and radiation field in the air and the ionosphere are calculated.Numerical results show the correctness and effectiveness of the proposed algorithm.2.According to the idea of plane wave decomposition of the radiation field,combined with method of the propagation matrix,the half-space radiation field expression is given when the linear antenna located in the atmosphere with a sinusoidal current distribution.This method can avoid the calculation of complicated Sommerfeld integrals,simplify the calculation process,and improve the calculation efficiency.Within a radial distance of 300 km from shore-based and airborne VLF line antennas,the radiation fields of shore-based and airborne VLF line antennas on the sea surface and within 20 m below the sea surface are calculated.Compared with the results of the traditional method(asymptotic method to solve Sommerfeld integral),it shows the correctness of the algorithm in this paper.3.Ray tracing in a inhomogeneous plasma is realized by solve the Haselgrove equation using the fourth-order Runge-Kutta method.The phase of the ray is calculated through the integration of the segmented path,and the polarization of the electromagnetic wave is calculated according to the refractive index gradient and the propagation direction.The changing characteristics of electromagnetic waves are simulated as they pass through a plasma medium.Combining the aperture integration and superposition principle,the effect of plasma plume on the far-field radiation pattern of satellite reflector antenna is analysed,and the attenuation of plasma plume to electromagnetic waves of different operating frequencies is calculated.4.The calculation scheme of the scattering characteristics is given when the plane wave enters the inhomogeneous plasma medium target.The selection of the incident reference surface,the selection of integration reference surface,ray tube division,physical optical integration and other specific algorithms is included.The electromagnetic scattering of inhomogeneous plasma sphere was calculated and compared with software of the Mieolot.The numerical results show that the algorithm in this paper is correct.The method in this paper is suitable for the analysis and calculation of the characteristics of the propagation and scattering of a general inhomogeneous plasma target.It is expected to be applied to the analysis of electromagnetic characteristics of supersonic weapons and rockets containing tail flames.