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

• Applicant: Professor Dr.-Ing. Martin Vossiek
• Subject Area: Communication Technology and Networks, High-Frequency Technology and Photonic Systems, Signal Processing and Machine Learning for Information Technology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 506408783

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.

• DFG Programme: Research Grants