Abstract
Multiple-input multiple-output (MIMO) radars and synthetic aperture radar (SAR) techniques are well researched and have been effectively combined for many imaging applications ranging from remote sensing to security. Despite numerous studies that apply MIMO concepts to SAR imaging, the design process of a MIMO-SAR system is non-trivial, especially for millimeter-wave (mmWave) imaging systems. Many issues have to be carefully addressed. Besides, compared with conventional monostatic sampling schemes or MIMO-only solutions, efficient image reconstruction methods for MIMO-SAR topologies are more complicated in short-range applications. To address these issues, we present highly-integrated and reconfigurable MIMO-SAR testbeds, along with examples of three-dimensional (3-D) image reconstruction algorithms optimized for MIMO-SAR configurations. The presented testbeds utilize commercially available wideband mmWave sensors and motorized rail platforms. Several aspects of the MIMO-SAR testbed design process, including MIMO array calibration, electrical/mechanical synchronization, system-level verification, and performance evaluation, are described. We present three versions of MIMO-SAR testbeds with different implementation costs and accuracies to provide alternatives for other researchers who want to implement their testbed framework. Several representative examples in various real-world imaging applications are presented to demonstrate the capabilities of the proposed testbeds and algorithms.
Highlights
The electromagnetic radio waves, which lie within the frequency range of 30 − 300 GHz, are typically known as millimeter-waves since they correspond to the wavelengths from 10 mm to 1 mm
We propose a practical multi-channel array calibration method to compensate for the gain and phase mismatches of the multiple-input multiple-output (MIMO) array elements
MIMO-synthetic aperture radar (SAR) SYSTEM MODEL we review the wave propagation model of the backscattered MIMO-SAR data, which forms the basis of the image reconstruction problem, present the geometrical setup for the proposed MIMO-SAR system, and introduce the mmWave sensor modules utilized in the testbeds
Summary
The electromagnetic radio waves, which lie within the frequency range of 30 − 300 GHz, are typically known as millimeter-waves (mmWaves) since they correspond to the wavelengths from 10 mm to 1 mm. The design process of a MIMO-SAR testbed must consider a wide variety of factors that will determine the quality of reconstructed images These include calibration, synchronization between the mechanical scans and radar transmissions, motion stability, lateral/range resolution, and accurate aperture sampling. In the presented MIMO-SAR imaging modality, which is implemented by scanning a MIMO mmWave sensor over a planar aperture, both amplitude and phase of the received signal over a wide bandwidth are recorded (coherent data) to mathematically reconstruct focused two-dimensional (2-D) or three-dimensional (3-D) (holographic) images. The image reconstruction techniques based on multistatic imaging modalities are necessary for the large MIMO apertures with spatially diverse transmit and receive antennas in SAR configuration In response to this major challenging requirement, we present and experimentally verify a series of state-of-the-art 3-D image reconstruction algorithms along with the mathematical derivations and demonstrate how to apply these algorithms to the testbed data.
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