Improving the Accuracy of Range Migration in 3-D Near-Field Microwave Imaging

Calibration measurements play a crucial role in improving the accuracy of both qualitative and quantitative microwave imaging. Ideally, in 3-D near-field imaging, a calibration measurement should be performed at each desired range (or depth) position, which can be very time-consuming. An analytical prediction of the range behavior of the resolvent kernel of scattering can reduce the calibration effort to a single measurement at a reference range position. Range-translation (or range-migration) analytical expressions are already widely used in far-zone radar and acoustic imaging; however, their accuracy deteriorates significantly in near-field scenarios. Here, we propose a range-migration technique for near-field microwave imaging with monostatic and bistatic measurement configurations. From a single measurement of the system point-spread function (PSF), the PSF magnitude and phase are accurately predicted at any desired range position. The proposed migration is performed in real space; however, it can also be applied with Fourier-domain (or k-space) inversion methods. Here, it is applied with quantitative microwave holography in simulation-based and experimental examples, which validate its performance and illustrate its limitations.