Near-Field Microwave Imaging Employing Measured Point-Spread Functions

Recently, real-time imaging methods have been proposed to quantitatively reconstruct the complex permittivity of an object. Two such methods, quantitative microwave holography (QMH) and scattered-power mapping (SPM), have been primarily used in near-field imaging; however, they are equally applicable to the less challenging scenario of far-field imaging. Both inversion strategies utilize linear approximations of scattering, which reduce the computation time to seconds even if the imaged volume contains millions of voxels—a feat not achieved by nonlinear quantitative inversion algorithms. The crux is in the system-specific point-spread function (PSF), which defines the transfer function of the linearized scattering model. A PSF measured with a known point scatterer supplies a quantitatively accurate transfer function, which enables the estimation of the complex permittivity distribution as a function of space. This work reviews the latest advances in quantitative real-time imaging along with simulation-based and experimental examples illustrating the methods’ accuracy and limitations.