Future driver assistance and autonomous driving systems require high-resolution 4D imaging radars that provide detailed and robust information about the vehicle's surroundings, even in poor weather or lighting conditions. In this work, a novel high-resolution radar system with 1728 virtual channels is presented, exceeding the state-of-the-art channel count for automotive radar sensors by a factor of 9. To realize the system, a new mixed feedthrough and distribution network topology is employed for the distribution of the ramp oscillator signal. A multilayer printed circuit board is designed and fabricated with all components assembled on the back side, while the radio frequency signal distribution is on a buried layer and only the antennas are on the front side. The array is optimized to enable both multipleinput multiple-output operation and transmit beamforming. A sparse array with both transmit and receive antennas close to the transceivers is realized to form a 2D array with a large unambiguous region of 130 • × 75 • with a maximal sidelobe level of −15 dB. The array features a 3 dB beamwidth of 0.78 • × 3.6 • in azimuth and elevation, respectively. Radar measurements in an anechoic chamber show that even the individual peaks of the absorber in the chamber can be detected and separated in the range-angle cut of the 4D radar image. The performance is validated by measurements of a parking lot, where cars, a pedestrian, a fence, and a street lamp can be detected, separated, and estimated correctly in size and position.INDEX TERMS Advanced driver assistance systems (ADAS), automotive radar, chirp sequence modulation, direction-of-arrival (DoA) estimation, frequency modulated continuous wave (FMCW), imaging radar, local oscillator (LO) feedthrough, mm-wave, multiple-input multiple-output (MIMO), time delay correction.This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.