Measurement time-optimized calibration procedures for very large antenna arrays of millimeter-wave radars

• Applicant: Professor Dr.-Ing. Christian Waldschmidt
• 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 512892854

For a few years it has also been possible to implement angle-generating radar sensors with very large absolute measurement bandwidths in the upper millimeter wave range. The array designs of the sensors meet the desire for ever higher angular resolutions with larger apertures. These arrays, some of which are several hundred wavelengths in size, are very difficult to calibrate with conventional calibration approaches or can only be calibrated with extreme effort, since the calibration has to be carried out with very small measuring steps. Two-dimensional arrays often cannot be calibrated as a function of the angle at all. A further complication is that the individual parts or section resp. of an array can be resolved over the large absolute bandwidths or in other words the array is several range resolution cells in size, and thus a coupling of the angle and distance information occurs in radar operation. Therefore, the focus of this project is the investigation of a fundamentally new calibration method for electrically very large arrays in the millimeter and sub-millimeter wave range. For this purpose, the Institute of Microwave Technology (MWT) proposes a new approach that uses an analysis of the modal representation of the arrays. In contrast to conventional calibration methods, this approach incorporates the physical behavior of the antennas into the calibration. Through a highly efficient representation of the physical antenna behavior, the new approach promises calibrations that are based on very few calibration measurement points and yet allow deep insights into the mechanisms of action that make calibration necessary in the first place. This approach will be explored as a novel calibration method that significantly reduces the measurement effort of calibration at the expense of computational effort. Furthermore, the limits of the method will be investigated, which measurement effort is necessary for the calibration depending on the array and which calibration quality can be achieved with it. The evaluation will be performed on different demonstrators and will lead to a comparison with conventional calibration approaches. One of the key issues of this project is the calibration with compact measurement setups. Therefore, it will be investigated how the calibration can be performed using measurement data from the near field. Furthermore, concepts for the use of partial subcalibrations to synthesize complete calibration data sets will be investigated. With the help of subcalibrations, electrically very large arrays are to be calibrated while maintaining the far-field condition, even with compact measurement setups.

• DFG Programme: Research Grants