Study On Wideband Electromagnetic Characteristics Of Stealth Targets In Low Frequency

The counterwork between stealth and anti-stealth is an important aspect in modern electric warfare. And the knowledge of radar targets scattering characteristics is the foundation to design stealth weapons and to develop anti-stealth radar systems. Based on the deduction that some wideband low frequency radars may have potential to detect stealth targets, the purpose of this dissertation is to investigate the wideband electromagnetic scattering characteristics of stealth targets in low frequency, using both prediction and measurement methods.Among the lots of electromagnetic scattering characteristics prediction methods, the finite-difference time-domain method (FDTD) was chose as the primary prediction method. Firstly, a versatile FDTD program for the calculation of wideband radar cross section (RCS) was developed. Than, aimed at the complex structure, electric large and low scattering characters of stealth targets, several memory and time efficient FDTD methods, conformal FDTD and auto meshing techniques were investigated exhaustively. The following are the key points: The reduced finite-difference time-domain method (R-FDTD) with a theoretic memory reduction of 33% in the storage of field components was used to solve scattering problems for the first time. Results generated by the R-FDTD method meet the regular FDTD's closely while saving about 33% computer memory. Thus, the capacity of PC to simulate electric large targets was greatly improved. The combination of R-FDTD with alternating direction implicit FDTD method (ADI-FDTD) to reduce both memory and time spending at the same time was discussed. The practical equations in 2-D domain were presented, while the 3-D's were under developing. The widely used FDTD meshing technique based on solid models with the aid of Auto CAD software was greatly accelerated using the octree representing method. As a supplement to the FDTD meshing technique based on solid models, which is not easy to combine with the FDTD program, a new meshing technique based on facet models was put forward. Using this technique, one can mesh most of the target models need not to care about what file format they use or where they come from.According to the model measurement aspect, we first introduced the electromagnetic similarities laws for scale measure, and than summarized several existing measurement methods when the ideal scaling relation is not satisfied because of the limitation of lossy frequency-dependent materials. At the same time, in the construction of the transientscattering measure system, a new method using a standard conductor sphere to calibrate the testing target's transmission function was used. Baesd on the transmission function, one can calculate the target's transient response under illumination of any pulsed plane waves. This method is very useful in practical engineering, because it avoids the trouble of measureing the real time waveform of the incident pulsed plane wave.Using the methods provided above, combined with the matured high frequency methods, the wideband harmonic and transient scattering characteristics of several typical stealth targets such as F-117A stealth fighter were investigated using both prediction and measurement methods. Perfect agreement between prediction results and measurement results could be observed. The research plays an important role in the development of anti-stealth radar systems: The wideband harmonic scattering data showed that stealth targets have very high RCS values in low frequency, and the ability of low frequency radars to detect stealth targets was proved; The wideband transient scattering data make it possible for low frequency radars to identify stealth targets.Finally, the wideband stealth effects of two new stealth techniques were studied. One is the non-specular scattering control by serrated edges; the other is the RCS reduction by plasma coating. For the former, a conductor plane was used as the example target, and the reduction of scattering from traveling wave and edge diffraction by geometric control of discontinuities...