Abstract
In radar systems, antenna arrays acquire direction-dependent information to localize targets or create images of the environment. However, because of unknown complex amplitudes per channel and mutual coupling, a calibration is necessary for good performance. Common calibration approaches measure to targets under known angles in a multipath-free far-field environment, which often can only be provided by anechoic chambers. Therefore, this process is not suitable for low-cost and frequent calibration. To overcome these limitations, this paper proposes a novel calibration approach using an unknown but sparse target scene. Multiple measurements at known relative positions of the radar are combined to a synthetic aperture. Then, the full mutual coupling matrix is estimated simultaneously with the unknown target scene. The method requires neither target position information, far-field conditions, nor an anechoic chamber because multipath propagation can be suppressed easily for targets located in the near-field. The proposed calibration approach is validated by measurements of a commercial 77GHz radar. The performance is evaluated by comparing the achieved image quality using the calibration results of this work and the radar’s ex-factory calibration data. The proposed novel calibration procedure improves the image quality, while considerably lowering the demands on the calibration measurements and environment.
Highlights
T ODAY, radar sensors are a key technology in many different fields such as the automotive sector [1], robotic applications [2], medical engineering [3], microwave imaging e.g. in security applications [4], and spaceborne radar [5]
In order to achieve a spatial resolution for radar imaging or angleof-arrival (AOA) estimation, synthetic aperture radars (SAR) [6], or antenna arrays in single-input multiple-output (SIMO), and multiple-input multiple-output (MIMO) systems are used [7]
In order to overcome the limitations of common approaches, we propose a low-effort near-field calibration for radar systems using a sparse but unknown target scene
Summary
T ODAY, radar sensors are a key technology in many different fields such as the automotive sector [1], robotic applications [2], medical engineering [3], microwave imaging e.g. in security applications [4], and spaceborne radar [5]. Mutual coupling was considered for online calibration in [30] and [31] These works assumed angle measurements, thereby implying multipath free far-field conditions. A low effort calibration procedure is necessary, which does neither require excessive multipath free far-field conditions, and an anechoic chamber, nor a reference system providing the target positions relative to the radar. In order to overcome the limitations of common approaches, we propose a low-effort near-field calibration for radar systems using a sparse but unknown target scene. This calibration significantly lowers the requirements on a multipath free environment and can be performed in most arbitrary environments. The measurement setup to validate the concept in a real world indoor setting as well as the calibration results are shown in Section IV, followed by a conclusion
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