IR homing sensors before the digital age where a piece of analog signalpath art. Its mostly rotating a singular ir sensor in 45degree and then mapping the inputs rotation compensated to the control surfaces. Simple at core but cant tell the difference between a jet exhaust, the sun, or a flare.
Modern version are boring is a High resolution ir cam and some blackmagic AI picking targets apart from flares.
source for the information in the title: i made it up, or did i?
Shellgame time