Читать книгу Inverse Synthetic Aperture Radar Imaging With MATLAB Algorithms - Caner Ozdemir - Страница 59

As given in Figure 2.4, the calculation of canonical‐shaped objects can be analytically approximately formulated. On the other hand, RCS calculation or prediction of complexly shaped objects is usually a difficult task. There exist some numerical approaches by which to estimate the RCS from arbitrarily shaped object. Some full‐wave approaches based on electric field integral equation (EFIE) or magnetic field integral equation (MFIE) techniques (Balanis 1982; Ergül and Gürel 2005) are used to calculate the scattering from electrically small targets. The common numerical technique used to implement such approaches is the well‐known method of moment (MoM) (Ekelman and Thiele 1980) technique. MoM‐based techniques are computationally effective when the electrical size of the target is on the order of, at most, a few wavelengths. At high frequencies when the size of the scatterer is much greater than the wavelength, however, the computation burden of MoM becomes problematic such that the computation time and the computation memory requirements are not manageable in simulating the scattering from electrically large and complex targets such as tanks, airplanes, and ships.

To cope with such targets whose electrical length is more than tens of wavelength, some asymptotic or hybrid methods (Kim and Thiele 1982; Ling et al. 1989) that combine different EM techniques in one simulator are used. The most famous one is called the shooting and bouncing ray (SBR) technique that can successfully estimate the scattering from large and complex platforms at high frequencies (Bhalla and Ling 1993, 1995). The SBR technique efficiently combines the geometric optics (GO) and the PO approaches (Knott 1993; Knott et al. 2004) to get the accurate estimation of the scattering (or the RCS) from large and complex objects at high frequencies and beyond (Ling et al. 1989; Weinmann 2006; Özdemir et al. 2014; Kırık and Özdemir 2019). An example of an RCS calculation from a complex airplane model is shown in Figure 2.5 where the RCS of a 14 m long airplane model is used for the simulation of the monostatic RCS. The calculation is done for the whole azimuth angles at the operating frequency of 2 GHz.