Near-Field Focusing Operators for Planar Multi-Static Microwave Imaging Using Back-Projection in the Spatial Domain

Abstract

Based on a plane-wave expansion of the observation data in quasi-planar multi-static scattering scenarios, an improved formalism for image creation utilizing back-projection in the spatial domain is derived. The underlying integral expressions for different focusing operators are derived analytically leading to magnitude correction factors, which are mostly relevant for reconstructing microwave images when the distance from the scattering object to the aperture plane is small. It is shown that the derived imaging procedure is superior to the traditional back-projection only compensating the phase delay of the measurement signals and validate our findings based on simulated as well as measured data. Since the derived focusing operators correspond to a low-pass filtering of the spatial images, the resulting modified multi-static back-projection algorithms effectively suppress imaging artifacts as well.

Figures (9)

• Figure 1: Visualization of the first imaging scenario containing 14 isotropic point scatterers. The simulation data in this case was synthetically generated using Hertzian dipoles for the Tx and Rx.
• Figure 2: Reconstruction results for the first simulation including 14 discrete point scatterers and ideal Hertzian dipole probes for the transmitting and receiving antennas. (a) Standard BPA without magnitude correction, (b) improved BPA.
• Figure 3: Scattering scenario simulated in CST MWS utilizing planar measurements and the perfectly electrically conducting HFT logo.
• Figure 4: Reconstruction results for the HFT logo. (a) Spatial image of the unfiltered MIMO-$\omega$-$k$-algorithm utilizing the code provided with Wang.Jul.2020, (b),(c),(d) back-projection algorithm.
• Figure 5: Visualization of the utilized Tx and Rx positions in the GO based ray-tracing simulation (a) as well as of the metallic plate containing several evaluation patterns (b).