Radar cross section prediction with finite difference time domain method


Thesis Type: Doctorate

Institution Of The Thesis: Gazi Üniversitesi, Fen Bilimleri Enstitüsü, Turkey

Approval Date: 2012

Student: FUNDA ERGÜN YARDIM

Supervisor: NURSEL AKÇAM

Abstract:

Radar Cross Section (RCS) is the measure of target' s ability to reflect radar signals in the direction of the radar receiver. In this study, the bi-static Radar Cross Section simulations of simple shapes such as a two dimensional square cylinder, a circular cylinder, an equilateral triangle and a complex aircraft model was carried out by using Finite Difference Time Domain (FDTD) method and Matlab 7.8 as the simulation environment. In order to obtain accurate and stable results in simulations, parameter selection is made by taking the numerical dispersion and the Courant stability conditions into account. FDTD problem space is terminated by Uniaxial Perfectly Matched Layer (UPML) which is one of the most flexible and effective absorbing boundary conditions described in the literature. For and cases, the reflection error is shown to be approximately at the level of -75 dB. Moreover in this study, the TF/SF formulation, one of the methods which effectively provide the contribution of the far field sources into FDTD method, is described in detail. The incident fields necessary for the implementation of Total Field/Scattered Field (TF/SF) formulation were obtained by using IFA method. For improving the performance of Incident Field Array (IFA) method, Matched Numerical Dispersion (MND) method was applied to two dimensional FDTD grid. Thus, by applying MND method to TF/SF wave source the field leakege into the scattered filed region is reduced by 200 dB for wide-band pulse excitations. Then it is shown that, by using a higher order cubic spline interpolation instead of linear interpolation in IFA method, the field leakage can be reduced about 70 dB. In RCS estimations, the far field radiations or scattered fields from the scatterers need to be found. In this study, the far filed electromagnetic fileds were calculated by using Near Field/Far Field (NF/FF) transformation technique from the near field FDTD data obtained by TF/SF formulation. In order to evaluate the effectiveness of scattering mechanisms depending on the frequency used, the target geometry and the electrical properties, first of all simple shapes such as a square cylinder, a circular cylinder and an equilateral triangle were studied. It is shown that, the RCS calculations can be done in Rayleigh, Resonance and Optical regions by the 2D-FDTD simulation. Finally, the RCS behaviour of an aircraft model composed of simple shapes as ellipse and triangle are investigated for different illuminations and different frequencies.