Studying Of Scattering Charactstics Of Targets Over Half-space Based On TDPO Method

Studying scattering characteristics of targets is of great importance in targets detecting and identifying. Generally, there are experimental and simulation based ways to research scattering characteristics of targets. Experimental research is the most fundamental way, but it is costly and difficult to take experimental measurements in some cases. Simulation methods mainly include analytical method, numerical method and high-frequency approximation method. The high-frequency approximation method is often used to analyze electrically large targets which are easy to deal with.Previous studies mainly deal with the case of free space. However, in modern warfare circumstance, penetrating aircrafts, missiles usually fly very low above surface of ground or sea. In these cases, the half-space influence cannot be ignored. In addition, the impact of ground or sea surface must also be considered in case of space-based radar. Usually, calculation about the electromagnetic scattering of targets above half-space involves half-space or layered half-space Green function. These Green functions involve complex Sommerfeld integrals which are extremely difficult to calculate the because of strong oscillation of the integrand. In case of multi-media consisted half-space, the related Green function will be more complex. Meanwhile, the analytic formula of Green function corresponding with up to four layered medium can be found in existing literatures. These complex analytic formula often bring lots of inconvenience for practical application.In this paper, the time-domain physical optics method is used to analyze electromagnetic scattering characteristics of targets over half-space. The physical optics algorithm is based on local principle, and there is no need to consider the electromagnetic mutual coupling relationship between every part of targets. So the algorithm takes the advantages of few unknowns, easy to use and fast to calculate. In half-space case, the incident wave on target includes direct incident waves and reflected waves from interface. The reflected wave can be obtained by Fourier Transform and inverse Fourier Transform. Compared to free space, the hide of surface element is also need to reconsider. After calculating the induced current on surface of targets, the far filed scattering of target can be equivalent with radiation of electric and magnetic dipoles. In this paper, the reciprocity theorem was used to get the radiation results of dipole above half-space. When the observation point is far from the half space interface, the surface and lateral wave can be ignored. In this case, only the direct incident wave and reflected wave are considered. The accuracy of time-domain physical optics which was used to deal with electromagnetic scattering problems of targets on half-space was studied and calculated in this paper. Through comparing with the physical optics of free space, the far field response of target on half-space was calculated. This method provides an efficient way to analyze the electromagnetic scattering characteristics of electrically large target over half-space.