Wow.

https://www.allaboutcircuits.com/news/teardown-tuesd
ay-hb100-doppler-radar-module/

"The PCB, itself, is a major component. Not only for the patch antennas
but also several RF filters, the local oscillator, and the mixer are all
largely made from peculiarly-shaped PCB tracks.

Apart from the PCB, there are only five "components" on the board.

Five passive components to implement a Doppler radar module. C'mon. You
have to be impressed by that!"

--
https://www.youtube.com/watch?v=9lSzL1DqQn0