Increasing 4-D Imaging Radar Calibration Accuracy Using Compact Antenna Test Range

The automotive industry perceives high-resolution radar sensors as one of the backbones of autonomous driving technology. With human safety being at stake, the topic of calibration is of the utmost importance. Yet, realizing possibly large volumes of accurate measurements of devices at 77 / 79 GHz, with 15 cm radiation aperture or more, is a challenge. Applying the Fraunhofer formula in such case results in a prohibitive direct far-field range length of 11.5 m. To address that issue, this paper introduces a new measurement system, consisting of a short-size focal length offset-fed compact antenna test range (CATR), interfaced with an analog echo generator. With a chamber size of only 0.9 m × 2 m × 1.6 m, the setup is designed to test apertures up to 30 cm size. Measurements are presented which involve a 4-D imaging radar on chip (RoC). Results obtained in the CATR and in a reference 7 m far-field range are compared and show excellent agreement. Reducing the cost and size of the test environment offers the possibility to measure more, and in particular to perform full angular calibrations, with the target being swept through the complete azimuth and elevation region. Such procedure is compared to a typically used diagonal calibration approach and is demonstrated to bring significant improvement in the compensation of sensor biases, with a 10 dB increase in peak-to-side-lobe ratio.