Spatial Averaging Technique for Improved MIMO Radar Calibration in Compact Antenna Test Ranges

With the increasing number of channels in integrated radar MMICs, radar modules and networks, beamformer calibration techniques must adapt to the physical dimensions of these sensors. Typical far-field calibration requires measurements at the Fraunhofer distance. This ensures a maximum phase error of 22.5° over the aperture. However, literature shows that phase errors below 5° are required for acceptable side-lobe suppression. Compact Antenna Test Ranges (CATR) create virtual far-field conditions in limited space but unfortunately they introduce magnitude and phase errors in their measurement. A method for calibrating MIMO radars in CATR settings is presented using spatial averaging to reduce these errors systematically. Simulations with a $\mathbf{1 6}$-channel FMCW radar show maximum errors of below 0.25 dB for magnitude and less than 2° for the phase with a single-digit number of spatial averages. Calibration with a $77-\text{GHz}$ MIMO radar sensor in the CATR confirms the technique's ability to mitigate test zone non-idealities, improving radar imaging quality.