Applications to Real Measured Data - Introduction to Imaging from Scattered Fields - page 124

(a) (b)

60 mm 20 mm 80 mm

ε r = 1.45

ε r = 1.45

ε r = 3 ε r = 3

30 mm 30 mm

(c) (d)

20 mm 60 mm 80 mm

ε r = 1.45

ε r = 3 ε r = 3 ε r = 1.45

Metal

30 mm 30 mm 28.5 mm

Figure 9.9 Shape and relative permittivity of Institut Fresnel targets: (a) FoamDielInt, (b) FoamDielExt, (c)
FoamTwinDiel, and (d) FoamMetExt.

the scattered field by subtracting the complex incident field from the complex
total field The inverse Fourier transform of the scattered field data gives a first
Born approximation reconstruction.

9.2.1 FoamdielInt
The FoamDielInt consists of two cylinders: a “foam” of relative permittivity
ε r ≈ 1.45 and inside the “foam” there is another circular dielectric of relative
permittivity ε r ≈ 3.0. Figure 9.8 shows the reconstruction from the inverse
Fourier transform of scattered field data, that is, the first Born reconstruction
of FoamDielInt. The Born reconstruction is computed at 6 GHz operating fre-
quency for which the scattering strength of the object is | kVa | ≈ 22. The object
represents a fairly strong scatterer, | kVa | ≫ 1, as a result of which we see that
the first Born reconstruction is not all that good.
Figure 9.10b shows the reconstructed image of FoamDielInt using the Born
approximation method. The reconstruction shows several undesirable arti-
facts and it also fails to give any meaningful (i.e., quantitative) values for
relative permittivity. The homomorphic filtering method was then applied to