Research On Near-field Scattering Modeling Of Ship On The Sea Surface Based On High Frequency Method

In order to safeguard the maritime rights and interests of our country and consolidate national defense security,the research on modeling technology of electromagnetic scattering of sea ships has always been a hot topic.The scattering problem of ships under X-band,which is the common frequency band in military,must be a near-field problem.Compared with the traditional electromagnetic scattering problems of far-field targets,the electromagnetic scattering problems of sea ships special relatively.Therefore,combined with computational electromagnetic method and near-field electromagnetic scattering theory,the near-field electromagnetic scattering model of sea ships based on the near-field criterion of targets is established,the characteristics and influencing factors of near-field scattering of sea ships are analysed,and the near-field scattering model of dynamic sea ships under serval typical scenarios are particularly simulated,and the modeling analyses of near-field scattering of sea-ship targets under actual engineering conditions are realized.Firstly,the study starts from the geometrical modeling of wind-driven sea surface based on sea spectrum,the dielectric constant of sea water and the six-degree-of-freedom motion model of ships on the sea formed by hydrodynamic action,which provides the necessary geometric model and parameter data for electromagnetic scattering of sea ships?Then,based on the electromagnetic scattering theory,the concept of the near field and the division between far field and near field are discussed,and the range of the near field in this paper is determined? Finally,the concept of radar scattering cross section(RCS)is extended to the near field,and a unified generalized radar scattering cross section(GRCS)is formed to describe the scattering characteristics of targets in both far field and near field.In view of the particularity of the near field,two typical near-field radiation sources are studied.Secondly,based on three common high-frequency methods,namely physical optics(PO),shooting and bouncing ray(SBR)and physical theory of diffraction(PTD),the cor-relation modification techniques for near-field scattering of targets is established,which mainly includes the scattering processing of expansion technique based on surface facets and two near-field meshing techniques,so as to realize the effective calculation of the near-field electromagnetic scattering contribution of the complex structures such as the flat region,the coupling region between facets,the wedge and the edge,etc.Compared with the numerical simulation,it is found that the mean absolute error(MAE)of the pro-posed model is less than 2 d B for simple targets(such as plates <0.5 d B and corner re-flectors <2 d B),and the MAE is less than 4d B for the actual scenarios of sea ship model,which meets the requirements of practical engineering simulation.Thirdly,based on the radar equation,the factors that affect the near-field scattering of the targets are analysed? based on the simulation model of near-field scattering,the effects of the radar range and radar antenna pattern on the near-field scattering of sea ships are studied,and the effects of near-field scattering characteristics from the dynamic sea ships and the antenna pattern incident are analysed.The results show that,compared with the far-field scattering,the near-field scattering of the targets is correlated with the radar range and direction pattern,and the dynamic variation of the generalized radar scattering characteristics may reach 20 d B.The research in this paper can expand the modeling of traditional far-field scattering of sea ships and the analyses of radar characteristics,and can provide necessary simulation and analysis means for near-field scattering of targets,missile target intersection and other scenarios.