Efficient 2-D Array Calibration of Radar Sensors in the Near Field by Modal Wave Expansion

In the pursuit of superb angular resolution, radar sensors with large-aperture antenna arrays are required. To ensure that the sensors deliver the best possible performance, high-precision angular calibrations are performed. However, the calibration effort increases with the aperture size, which is drastically aggravated in case of two-dimensional arrays which are required for four-dimensional imaging. Additionally, the far-field condition is violated due to the large aperture, introducing errors which cannot be neglected. In order to account for near-field effects, this paper proposes to expand the established, efficient modal wave expansion method. For that, prior knowledge about the antenna positions is employed, such that the measurement of only two planes is required. Limits are derived mathematically and demonstrated by simulations and measurements with a 79 GHz radar sensor. In this work, five radar measurements were sufficient to determine the phase centers of an 2-D array.