An Elliptical Bipolar Cylindrical Coordinates Based Mixed Domain Near-Field Imaging Algorithm for Scanning 1-D Non-uniform Sparse MIMO Arrays

The millimeter-wave (MMW) 3-D imaging technology with mechanically scanned 1-D non-uniform sparse multiple-input-multiple-output (MIMO) arrays has been extensively researched due to its advantages in near-field applications. In this paper, an accurate and efficient spatial-frequency mixed domain imaging algorithm based on the elliptical bipolar cylindrical coordinates is proposed. The algorithm relaxes the array constraints present in the traditional frequency domain algorithms by decomposing the MIMO synthetic aperture radar (MIMO-SAR) system into bistatic SAR subsystems. Furthermore, an elliptical bipolar cylindrical coordinate system is proposed to address the space-variant characteristics of the spectrum in the bistatic SAR subsystems, thereby enabling efficient imaging of the subsystems using frequency domain techniques without further approximations. The final imaging result is obtained through coherent accumulation of the reconstructed subimages of all bistatic SAR subsystems in the spatial domain. Compared with existing algorithms, the proposed algorithm is applicable to MIMO-SAR systems with scanning 1-D non-uniform sparse MIMO arrays and large field-of-view while maintaining high computational efficiency and image quality. The performance of this algorithm is validated through numerical simulations and experimental results.