Refinement Research On Algorithms And Applications Of High-frequency Electromagnetic Scattering From Complex Targets

As one of the key technologies of radar confrontation, the accurate prediction and interpretation of radar target characteristics has very important significance in the military field. Researches on radar target characteristics include two aspects:electromagnetic scattering and inverse scattering. To predict the target scattering characteristics through computer simulation has aroused great concern of many radar workers. Compared with the numerical methods such as MoM, the high-frequency methods have the advantage of quick computing speed and occupying less computing resources, thus they already have a wide application in feature prediction of electrically large radar targets and targets existing in complex environment. In addition to obtaining the electromagnetic characteristics of known targets, people also concern the problem of extracting geometry and physically relevant information from the characteristics of unknown targets, which can be used for the target classification and recognition. The high-frequency scattering of an electrically large target can be well approximated as a sum of response from individual scattering centers. The scattering center model can provide a concise and physically relevant description of the target radar signature. We use the attribute scattering center model to represent the targets’high frequency back scattering. In this model, the backscattered field of an individual scattering center is described as a function of frequency and aspect angle, and the total scattered field from a target is then modeled as the sum of these individual scatterers. It provides a physical description of target scattering centers via a set of parameters.Based on the hybrid geometric optics and physical optics (GO-PO) method, we present the research on ray tracing and field prediction method of multi-reflection rays. The radar cross section (RCS) and synthetic aperture radar (SAR) image characteristics of some targets are predicted by using the high-frequency method. We present a forward approach to establish parametric scattering center models for known complex radar targets. In this approach, an automatic technique based on ray tracing and clustering is first developed to extract scattering centers directly from the computer-aided design (CAD) model of the targets. Following this, a set of forward methods is developed to determine the physically relevant parameters of two-dimension (2-D) attributed scatterers, such as type, amplitude, position and length. Finally, this approach is validated through the parametric model establishment of two complex targets and good agreement has been demonstrated between the reconstructed and actual radar characteristics. Different from the familiar inverse extraction approaches, the proposed approach provides a new forward way of constructing radar targets’feature database based on2-D parametric scattering center model, which will ultimately facilitate the feature matching in the SAR automatic target recognition (ATR) system.The main content of this paper includes the following parts:1) We present the PO method and the hybrid GO-PO method which are used for the characteristic prediction of complex radar targets. Based on the high-frequency methods, we have simulated the RCS and SAR image characteristics of electrically large targets in free space and in sea environment.2) We present a new method based on ray tracing with PO to extract the scattering centers directly from the target CAD model. The scattering center extraction approach includes ray tracing and clustering, field prediction and scattering center sorting and selection. Backscattering of each scattering center can be analyzed separately by using the proposed method.3) We present a forward approach to establish parametric scattering center models for known complex radar targets. We develop a set of forward algorithms to determine the model parameters including relative amplitude, frequency dependence, position, and length. By locating the equivalent reflection point of each ray based on the optical path difference equivalence principle,3-D scattering center position can be calculated by weighting the reflection points of all contributive rays, which is an important innovation of this dissertation.4) We have studied the parametric models of flat targets owning different shapes. The modeling method is applied to the parametric modeling of a missile target in free space, which is used to inversion target flight attitude.