Radio Science Bulletin 313 - June 2005 - URSI

Backward Scattered Field0.010.0080.0060.0040.0020-0.002-0.004-0.006-0.008jωa /c43.532.521.510.5MPMSS1SS2-0.010 10 20 30 40 50 60 70 80 90 100Time [nsec]Figure 18. Back-scattered time-domain field for adielectric sphere ( ε r = 4 and a 0.5-m radius).Gaussian window are σ = 0.56 and ct0 = 5σ. The inversetransformedtime-domain data, which provides anapproximate band-limited impulse response for the structure,is shown in Figure 18.The extracted poles are almost the same for all threemethods, with small differences apparent for SS2 (NSIG =10 in Figure 19). The -80 dB threshold is satisfied with 10damped sinusoids for each method (Figure 20). The averageCPU times for the MPM, the SS1, and the SS2 are 18.1 s,25.8 s, and 341.1 s. Since the time for the MPM is about70.11% of that for the SS1 and 5.30% of that for the SS2,the MPM performs faster than the SS1 and SS2.0-0.25 -0.2 -0.15 -0.1 -0.05 0α a /cFigure 19. Extracted poles for NSIG = 10 for adielectric sphere with ε r = 4 and a 0.5-m radius.The x-axis and y-axis represent the real and theimaginary values of the pole, normalized withrespect to the radius a of the sphere, and c is thespeed of light in free space.positive x-axis and is y-polarized. In this example, theGaussian window is specified by σ = 0.45 and ct0 = 5.1σ.The inverse-transformed time-domain data is shown inFigure 22.5.5 Composite Metallic-DielectricSphereThe last example is a composite sphere of radius 0.5m (Figure 21). The bottom half of the sphere is a perfectconductor, and the top half is a dielectric with ε r = 4 . Theback-scattered field has been calculated using WIPL-Dfrom 10-1500 MHz. The incident field arrives along theFigure 21. A composite dielectric sphere withr = 0.5 m, a perfectly conducting bottom half,and a dielectric top half ( ε r = 4 ).-55-60MPMSS1SS20.040.03RMSE [dB]-65-70-75Backward Scattered Field0.020.010-80-0.01-851 2 3 4 5 6 7 8 9 10NSIGFigure 20. RMSEs of the reconstructed signal fora dielectric sphere.-0.020 10 20 30 40 50 60 70 80 90 100Time [nsec]Figure 22. Back-scattered field in the time domainfor a composite sphere.36TheRadio Science Bulletin No 313 (June, 2005)