Yeah........ I should have just typed Sidewinder.
A former coworker of mine would be disappointed, he designed the first seeker for the original AIM-9 :)
They are now, but if you're making a stealth-seeking guidance package, you'd want to think outside the box a bit.
Physics gets in the way...tough to get reasonable gain, or any substantial directivity when the wavelength is 50x the diameter of the missile.