Baseband and Super-Resolution-Passband Reconstructions in Microwave Imaging

Resolution of depth imaging depends on the bandwidth of the signal used for illumination. The differences between using baseband and passband signals have not been adequately investigated in the literature. It is shown in this contribution that only baseband signals, whose spectra include all frequency components from a certain upper limit down to zero (dc), are capable of depth-image reconstruction for arbitrary variations of the imaged material property (e.g., permittivity in microwave imaging). On the other hand, the technically more feasible passband illumination, with both lower and upper frequency limits, is only suitable for the reconstruction of images that contain abrupt, or at least very sharp, changes in the imaged material property. Fine gradual variations between such abrupt changes are not accurately captured in this case. For objects with material abrupt changes only, as, e.g., stratified media, a recently developed super-resolution technique in conjunction with passband illumination is applied for image reconstruction. Resolutions far beyond the Rayleigh limit have been obtained for both noiseless and noisy data.