Comment by sorenjan
BMW has a page describing the use of UWB (Ultra Wide Bandwidth) radio in key fobs and how it helps against relay attacks. In short it's because the wide bandwidth allows for very short pulses which lets them measure the distance between the car and the key, and using a relay will inevitably add distance and therefore time between the signal is sent and the reply is received.
https://www.bmw.com/en/innovation/bmw-digital-key-plus-ultra...
I believe this was ratified into a standard so it should show up in more new cars. https://carconnectivity.org/car-connectivity-consortium-publ...