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Theoretical And Experimental Studies On The Composite Electromagnetic Scattering Of The Chaff With Aircraft

Posted on:2023-12-25Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y C ZuoFull Text:PDF
GTID:1522306911981019Subject:Electromagnetic field and microwave technology
Abstract/Summary:PDF Full Text Request
Chaff cloud is a passive jammer that is widely used in a variety of air combat scenarios.When the aircraft comes under attack,chaff clouds are released to realize interference.The electromagnetic scattering evaluation of a chaff cloud and its composite scattering with the aircraft is the foundation of the jamming effectiveness analysis.When dealing with the mentioned scattering evaluation issue,one must deal with three main problems: first,it is difficult to establish the geometric models of the chaff cloud that diffuses within the airflow.Secondly,it is difficult to estimate the electromagnetic scattering of the chaff cloud and its composite scattering with the target.Thirdly,it is difficult to make a controllable physical model of a chaff cloud in real scattering tests.This thesis is presented to solve partially these problems.When large amounts of chaff elements are released from the carrier,they diffuse and settle due to the influences of complex airflow.In this thesis,Navier Stokes equations and finite-difference time-domain method are used to describe the diffusion process of the chaff cloud in airflow.Essentially,Chaff cloud is an electrically large target that is composed of a large number of perfectly conducting thin elements.These elements are electrically small objects.In this thesis,the electromagnetic scattering properties of chaff cloud are evaluated by using the improved vector radiative transfer theory which can be solved by a parallel Monte Carlo algorithm.When dealing with the composite scattering of a chaff cloud with an aircraft,this thesis statistically rewrites the high-frequency bouncing ray method,and integrates it with the parallel vector radiative transfer theory from the aspect of statistics.Regarding experiments,this thesis designs and facilitates a chaff element inserting machine to provide controllable chaff cloud models.Furthermore,the scattering matrix,attenuation constant,relative dielectric constant,and permeability of chaff clouds are measured,which provides support for the theoretical studies of chaff cloud.Firstly,this thesis collects the academic achievements related to geometric modeling,scattering calculation,and measurements of chaff clouds.From open literature,the abroad initial research about the chaff cloud is published earlier then domestic ones.Many research developments are already used in practice.In recent decades,native scholars have provided a lot of research about chaff cloud,but there still exists a technical gap between native and foreign scholars,especially on some kernel techniques,such as chaff cloud dynamic diffusion modeling,fast scattering estimation,chaff designing,etc.This thesis also points out that both native and overseas scholars have done insufficient works on chaff cloud diffusion modeling in aircraft wake,composite scattering calculation of the aircraft with chaff cloud,and controllable scattering tests for chaff cloud.Based on the mentioned analysis,this thesis carried out studies to solve partially these problems,which are also the main innovations of this thesis.Secondly,regarding the geometric modeling of a released chaff cloud with an aircraft,this thesis establishes the velocity distribution models for different types of aircraft,the chaff cloud is treated as a dielectric mass,and the dynamic diffusion process of chaff cloud is described based on Navier Stokes equation and finite-difference time-domain method.This thesis takes account of two typical releasing scenarios.Simulations show that the spatial numerical density of the chaff elements in the scenario of jet-released is mainly affected by the aircraft wake,and the aircraft wake has little effect on the diffusion of explosive-released chaff elements.Compared with the actual recorded images,the presented chaff cloud model can well describe the real scenarios,which also provides a foundation for scattering evaluation of the chaff cloud.Thirdly,the vector radiative transfer theory is used to calculate the scattering of the chaff cloud.This method is originated from the principle of energy conservation and can effectively consider the coupling effect between chaff elements.The Monte Carlo method is selected to solve the vector radiative transfer equation.In this method,the incident energy is assigned to several virtual particles.These particles go through the attenuation and scattering process in the chaff cloud according to the statistics and the scattering theory of a single chaff element.These particles are emitted from a virtual source plane,which ensures the plane wave properties of the emitted particles.When considering the radiation pattern of the transmitting antenna,the energy distribution on the source plane is no longer uniform,so the acceptance-rejection method is used to describe the energy non-uniformity of antenna emission.The scattering characteristics of single chaff and the loss characteristics of the chaff medium are calculated by the method of moments.Compared with the measured results,the proposed algorithm can effectively calculate the scattering of the chaff cloud,and the error is less than 21%.Then,regarding the algorithm verification and scattering measurement of the chaff cloud and target,this thesis proposes a self-designed controllable chaff inserting machine.It makes the physical models of the chaff clouds with the strategy of "mosaic",and realizes the reliable correspondence between the simulation model and the measured one.The test principles of polarization scattering,attenuation characteristics,and mixed medium characteristics are studied.The test results show that the elements in the polarization scattering matrix with uniformly oriented chaff are numerical near with each other,and the shape of chaff cloud also affects its polarization scattering properties.When the chaff numerical density is 96000 elements per cubic meter,the scattering coefficients and attenuation coefficients of cloud clusters are distributed in the order of one-tenth to one percent,and these coefficients are not sensitive to the polarization angle.The relative permittivity and permeability of the chaff and air mixture with different elements number and distributions properties are measured by the waveguide method.The measurement results show that the values of the relative permittivity and permeability of the mixture of several chaff elements and air are close to that of air,which also shows that the scattering ability of small-scale chaff cloud is very weak.Finally,regarding the composite electromagnetic scattering between chaff cloud and the aircraft,this thesis statistically rewrites the SBR method.Based on the vector radiative transfer theory,the incident wave is discretized into a series of particles,which carries the frequency,polarization,and phase information of the incident wave.These particles interact with the aircraft according to the ray incoherent principle and Fresnel’s reflection law.The particles’ shuttle between the chaff cloud and the aircraft can take into account the electromagnetic coupling between them.The particle’s walking,attenuation,and phase shift are caused by the interaction with the chaff or the aircraft.The total energy is obtained by summing coherently the scattering information of all particles.The error of this method compared with the experimental one is less than 20%.More simulations show that the composite scattering between chaff cloud and aircraft is very weak,and the main issue affecting the composite scattering is the shielding effect.In sum,to meet the needs of chaff interference,this thesis studies the electromagnetic scattering of aircraft with chaff cloud,improves the chaff cloud diffusion modeling method in aircraft wake,employs parallel scattering computing technology for large-scale chaff cloud,provides controllable physical model making technology for chaff cloud.This thesis also proposes measurements theory for polarized scattering,attenuation,equivalent medium properties of the chaff cloud,these studies provide support for chaff cloud jamming effectiveness evaluation.
Keywords/Search Tags:Chaff cloud, composite scattering, vector radiative transfer theory, scattering experiment, diffusion modeling
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