3D near-field (NF) passive radar imaging approach for complex environments is presented. It utilizes frequency domain inverse source solutions and spatial image generation by coherent superposition of the automatically phase corrected single-frequency images. 3D near-field (NF) passive radar imaging approach for complex environments is presented. It utilizes frequency domain inverse source solutions and spatial image generation by coherent superposition of the automatically phase corrected single-frequency images.A The fields scattered from the imaging scene together with the fields radiated from the illuminating transmitter (Tx) are captured through NF measurements. The single-frequency inverse source solutions reconstruct simultaneously equivalent surface sources for the (Tx), the targets of interest (TOIs), and possibly present echo scatterers, which are subsequently separated due to its spatial localization. Spectral representations are computed for the Tx and TOI sources and single-frequency 3D images are obtained by hierarchical disaggregation. Finally, the single-frequency images are coherently superimposed utilizing an appropriate phase correction methodology. The phase correction is derived from the reconstructed Tx sources and compensates for the spatially varying phase shifts between the Tx and the scatterers, as well as for delays caused by the measurement instrumentation. Both numerical simulations and experimental measurement results are shown to validate the feasibility of the approach.

The quality of antenna and radar cross section measurement chambers is strongly dependent on the absorption behavior of the installed wave absorbers. It is demonstrated that the behavior of the absorbers can be assessed and illustrated with excellent spatial resolution by powerful microwave imaging techniques. When the absorbers are subjected to an illumination source, the fast irregular antenna field transformation algorithm (FIAFTA) enables simultaneous reconstruction of equivalent sources for both the illuminating source and the scatterers from near-field measurements. This process effectively implements echo suppression, allowing for the isolation of weakly scattered fields, primarily caused by the wave absorbers. Building upon this foundation, the application of microwave imaging technology enables the visual representation and examination of the absorbers. Experimental measurement results are shown to validate the feasibility of the approach.