Abstract
Microwave and millimeter-wave measurements acquire total-field responses from measurements, yet imaging algorithms instead require the data in the form of scattered-field responses. Two approaches exist for the extraction of the scattered-field data from the total-field responses, namely, the Born and the Rytov data approximations. It is well known that, depending on the target’s size, contrast, and structural complexity, one approximation can achieve an improved accuracy over the other. Yet, the Rytov approximation is rarely used in microwave and millimeter-wave imaging, likely due to phase-unwrapping problems occurring in the case of strongly heterogeneous electrically large targets. Here, we propose a method to utilize the Born and the Rytov approximations simultaneously in a single inversion step for real-time imaging with quantitative microwave holography (QMH). We show through examples with simulated and experimental data that in near-field imaging scenarios, including the imaging of a breast-tissue phantom, there are significant benefits in employing the new method.
Highlights
M ICROWAVE and millimeter-wave imaging methods have been extensively developed over the last halfcentury, with the more recent focus being on close-range imaging, such as concealed weapon detection and security inspection, through-the-wall imaging, nondestructive testing, and biomedical imaging [1]–[11]
Consider the application of the forward model (6) to the case of monostatic and/or bistatic scenarios, where the Rx and Tx antennas in each j k pair are in a fixed mutual position, i.e., rTx and rRx can be described by a single position vector r relative to the scanned object under test (OUT)
We propose a method of utilizing the Born and Rytov approximations in tandem in a single reconstruction step where unwrapping the total-field data is not necessary
Summary
M ICROWAVE and millimeter-wave imaging methods have been extensively developed over the last halfcentury, with the more recent focus being on close-range imaging, such as concealed weapon detection and security inspection, through-the-wall imaging, nondestructive testing, and biomedical imaging [1]–[11]. The mathematical models of electromagnetic (EM) scattering are critically important for accurate image reconstruction They utilize a variety of approximations in their kernels, i.e., the total electric field and/or Green’s function, to reduce the computational complexity [9]. Errors in this extraction are as detrimental to the image quality as measurement noise and uncertainties or errors in the total-field and Green’s function distributions This has motivated significant research effort in comparing the Born and Rytov approximations as strategies for scattered data extraction [15]–[17]. We note that the proposed approach of combining Born’s and Rytov’s data approximations is in principle applicable to any image reconstruction method where the scattered-field response is extracted from total-field measurements. An experimental example further demonstrates the benefits of utilizing both approximations in tandem
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