typical car radar has very simple active RX array. A few, maybe up to 10, depending on the price of frontend and power of DSP, equally separated active receiving antennas. each is usually a passive microstrip patch array, usually taped for higher gain in horizontal direction.
Do you remember the incident with Tesla getting under the high trailer, with driver's head cut off. That was because the gain was too high, and the beam missing high obstacles.
I have not seen an automotive array with vertical scanning yet.
The TX is even simpler. It may be just one tapped element for wide angle excitation, or a pair for higher front gain, or a pair of pairs for sensing wide, and narrow space in front of the car. Since it is sometimes hard to separate and position targets, it can be done with different RX antenna profiles, for better certainty.
There may be one extra RX pair probably for power calibration, and/or interfering radar sensing.
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