Fundamental investigations concerning the analysis, detection, and compensation of calibration errors in MIMO radar and MIMO SAR imaging systems

在雷达系统领域，MIMO-SAR概念(MIMO=多输入多输出；SAR=合成孔径雷达)变得越来越重要。在这个概念中，具有多个发射和接收天线的雷达传感器或目标沿弹道移动。在下文中，在沿轨迹的多个点记录的来自所有发射和接收组合的测量信号集被重建为图像。MIMO-SAR的应用可以在遥感、地面和空中车辆周围的成像，或在安全和医疗技术中找到。MIMO雷达的测量总是受到MIMO阵列中的缺陷的影响，例如，由于天线单元之间的相互耦合，或者不正确地假设天线位置和相位中心。为了将这些损害降至最低，在调试之前对阵列进行了校准。除了高质量校准成本高且并非总是可能的事实外，参数还会随温度、环境和老化而变化。因此，MIMO雷达系统总是处理容易出错的测量。在典型的MIMO合成孔径雷达测量中，MIMO阵列以大约恒定的间隔移动到不同的位置。当考虑得到的总体测量数据集时，它现在受到由不完美校准的MIMO阵列引起的周期性测量误差的影响。因此，来自每个目标的信号被调制，产生确定性误差，从而导致在雷达图像中出现幽灵目标。类似的误差也出现在用于未来成像雷达系统的大规模MIMO阵列中。虽然图像质量和目标检测概率可能会显著下降，但到目前为止，这种影响几乎没有文献记载和理论分析。因此，本项目的目的是系统地研究定标误差对MIMO SAR系统的基本影响。这将通过分析、模拟和测量来完成。将推导出允许精确描述由校准误差引起的幽灵目标的模型和计算方法。从而为在实际条件下更好地评估成像MIMO SAR系统的测量结果提供了基本依据。此外，还将研究如何设计多输入多输出合成孔径雷达孔径和测量程序，以便即使存在校准误差，也能最大限度地减少幽灵目标的出现。另一个方面是研究如何将校准误差的确定性结构作为一种新的度量，一方面在进行中的雷达运行期间评估天线阵列的现场校准质量，另一方面改进或评估校准过程。

In the field of radar systems, MIMO-SAR concepts (MIMO = multiple-input multiple-output; SAR = Synthetic Aperture Radar) become more and more important. In this concept, radar sensors with multiple transmit and receive antennas or the target move along a trajectory. In the following, the sets of measurement signals from all transmit and receive combinations, recorded at multiple points along the trajectory, are reconstructed to an image. Applications of MIMO-SAR can be found in remote sensing, in the imaging of the surroundings of ground and air vehicles, or in security and medical technology. MIMO radar measurements are always impaired by imperfections in the MIMO array, for example because of mutual coupling between the antenna elements or incorrectly assumed antenna positions and phase centers. To minimize these impairments, the arrays are calibrated prior to commissioning. Apart from the fact that high-quality calibration is costly and not always possible, parameters change depending on temperature, environment and aging. As a result, MIMO radar systems always process error-prone measurements. In a typical MIMO SAR measurement, the MIMO array is moved to different positions with approximately constant spacing. When considering the resulting overall measurement data set, it is now affected by periodic measurement errors caused by the imperfectly calibrated MIMO array. As a consequence, the signals from each target are modulated, yielding deterministic errors that result in the appearance of ghost targets in the radar images. Similar errors also occur in large scale MIMO arrays, that are intended for future imaging radar systems. Although the degradation of image quality and target detection probability can be significant, this effect has so far hardly been documented and theoretically analyzed. Therefore, the aim of this project is to systematically investigate the fundamental effects of calibration errors on MIMO SAR systems. This will be done analytically, in simulations, as well as by measurement. Models and calculation methods will be derived that allow an exact characterization of the ghost targets induced by calibration errors. The targeted results thus provide a fundamental basis to enable the better assessment of measurement results of imaging MIMO SAR systems under realistic conditions. In addition, research will be conducted on how MIMO SAR apertures and measurement procedures should be designed so that the occurrence of ghost targets is minimized even if calibration errors are present. Another aspect is to investigate how the deterministic structure of calibration errors can be used as a novel metric to assess the quality of the calibration of an antenna array in situ during the ongoing radar operation on the one hand, and to improve or evaluate calibration procedures on the other hand.