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[[Image:ART RCS3.png|thumb|left|480px|Figure 3: Variation of normalized back-scatter RCS (σ/λ<sup>2</sup>) of a thin metal square plate of dimensions 0.3λ<sub>0</sub> × 0.3λ<sub>0</sub> as a function of elevation angle θ for the case of an incident TEz (Eφ) polarization, solid red line: [[EM.Libera]] results, solid blue line: [[EM.Tempo]] results with a zero-thickness plate, solid green line: [[EM.Tempo]] results with a 0.01λ0 thick plate, red symbols: simulated data using the finite element method (FEM) presented by Ref. [1].]]
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Next, we investigate the variation of RCS of a metal plate with its lateral size or frequency. For this purpose, we consider a thin metal (PEC) plate of dimensions a × a (same as shown in Figure 1), and compute its backscatter RCS as a function of k<sub>0</sub>a, where k<sub>0</sub> = 2 π / λ<sub>0</sub> = 2 π f / c. A plot of RCS vs. k<sub>0</sub>a shows the variation of RCS with frequency when the plate's lateral size a is fixed, or alternatively, the variation of RCS with the lateral dimension at a fixed frequency. Figure 4 shows the variation of the backscatter RCS of the square PEC plate with k<sub>0</sub>a as simulated by [[EM.Libera]]. These results are compared with measured data reported by Ref. [2]. Excellent agreement is observed between the two sets of data. The figure also shows the backscatter RCS data computed by [[EM.Illumina]]'s Physical Optics (PO) solver. It is seen that the PO results do not agree well with the full-wave MoM results until the size of the plate grows to about a wavelength or more. This can also be interpreted as when frequency increases such that k<sub>0</sub>a > 6, which justifies the physical optics approximation.
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[[Image:ART RCS4.png|thumb|left|480px|Figure 4: Variation of normalized back-scatter RCS (σ/λ<sup>2</sup>) of a thin metal square plate of dimensions a × a as a function of k<sub>0</sub>a (normalized plate length or normalized frequency) for the case of a normally incident plane wave source, solid red line: [[EM.Libera]] results, solid blue line: [[EM.Illumina]] (PO) results, red symbols: measured data referenced by Ref. [2].]]
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