A novel technique for reducing the imaging domain in microwave imaging of two dimensional circularly symmetric scatterers

Abstract

A novel technique for reducing the imaging domain in microwave imaging of 2D circularly symmetric scatterers is presented. The degree of symmetry vector of the measured scattered field is employed for the purpose of localizing the scatterer. The degree of symmetry for a transmitter position is computed as a function of the difference between the first half and the spatially reflected second half of the measured scattered-field vector. The symmetry plots exhibit unique features of the direction and distance to the scatterer from the centre of the imtances from the centre, permittivities, and radii are studied, which enables the localization of the cylinder in the imaging domain I, thereby allowing the reduction of the imaging domain to I r . Some typical symmetry plots are considered in Figure 3, where the symmetry plots have been generated from noisy measurement data with an SNR of 30 dB. The symmetry positions are 19 and 44. The distances between the asymmetry positions through 19 and through 44 along the measurement circle are more different in Figure 3(b) than in Figure 3(a). The peak values at the asymmetry positions are much smaller in Figure 3(a) than in Figure 3(b), indicating that the circularly symmetric scatterer is very close to the origin in the first example and farther away from the origin and closer to the transmitter position 44 in the second case. In the case of Figure 3(c), the degree of symmetry values for all the transmitter positions are very small, thus indicating that the object centre and the centre of the imaging domain coincide. The reduced imaging domains in the three cases are chosen accordingly, as indicated in Figure 4. The Newton-Kantorovich procedure has been employed for the imaging of the approximately located scatterer. Figure 5(a) shows the actual profile of a 2D circularly symmetric dielectric scatterer. Its degree of symmetry values for the different transmitter positions are plotted in Figure 5(b). Figure 5(c) shows the reconstructed image after the sixth iteration of the Newton-Kantorovich procedure when the entire imaging region is employed. The reconstructed image when the reduced imaging region is employed, as shown in Figure 5(d). The result obtained using the proposed technique is seen to be much better. There is also a considerable reduction in computation time, as compared to the case where the entire imaging domain is employed.