Due to the fact that the imaging distance is similar to the dimension of synthetic aperture antenna in near-field, the Fourier imaging theory used in the traditional synthetic aperture imaging radiometer (SAIR), which is based on the far-field approximation, is invalid for near-field synthetic aperture imaging. This paper is devoted to establishing an accurate imaging algorithm for near-field millimeter wave SAIR. Firstly, the near-field synthetic aperture imaging theory is deduced and its relationship to the far-field imaging theory analyzed. Then, an accurate imaging algorithm based on the near-field imaging theory is established. In this method, the quadratic phase item and antenna pattern are taken into consideration, and the image reconstruction is performed by minimizing the Total-Variation norm of brightness temperature image, which reduces the influence of the visibility observation error and improves imaging precision. Finally, the effectiveness of the proposed imaging algorithm has been tested by means of several simulation experiments, and the superiority is also demonstrated by the comparison between it and the existing Fourier transform methods. The results demonstrate that the proposed method is an efficient, feasible imaging algorithm for near-field millimeter wave SAIR.
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