An Improved Antenna Calibration Methodology for Microwave Diffraction Tomography in Limited-Aspect Configurations

This work underlines the importance of properly modeling the directivity of the antennas and proposes an improved calibration strategy in the framework of microwave diffraction tomography. Experiments to prove the effectiveness of the approach are carried out with a system comprising two ultrawideband linear antenna arrays. In the configurations presented herein, targets are in the near-field of the arrays and small aperture angles are considered ( ~ 40 deg). Multi-frequency multi-view multi-static quantitative inversions are performed using the modified
²
gradient method. The calibration approach reconstructs the directivity of the antennas using measured incident fields. The novelty consists in taking the reconstructed antenna pattern into account within the inversion algorithm both at transmission and at reception through a multipolar expansion of, respectively, the incident field and the data equation Green function. The results show that a fine modeling of the directivity of the antennas is paramount to image and separate scatterers, particularly when placed closer than the resolution limit of the system and beyond the Born approximation regime.