Isn't the ISS supposed to be the most complicated machine ever built by humans?
I usually hear it as "one of the most expensive single projects" rather than the most complex. I'd bet there any many more complex, the LHC comes to mind.
ie there's lots of fun applications for radar, some of them have very complex math involved in manufacturing processes. Then you got automotive radar, you mainly need to get the position and velocity of some objects, the math is simpler. But you have to certify that stuff for ASIL-D, no one makes you ASIL-D radars, so you combine multiple radars. 3'Bs make a D as the saying goes.. Then you gotta worry about BOM costs because you want to ship 10 million cars..