The  Alamo R-27P is a passive anti-radiation missile, similar to the US/NATO "Shrike" missile.  One more variant of the R-27 is an R-27P missile with a passive seeker.  Both The R-27P and R-27EP employ a 9B-1032 X-band passive anti-radiation seeker This is an anti-radar homing missile launched against aircraft using active radars, such as AWACS and jamming aircraft, as well as to force opposing fighters to secure their radars. The missile has a long-range variant with an extended range engine designated the R-27PE.


Source: http://military.wikia.com/wiki/Vympel_R-27_Alamo; http://defenceforumindia.com/forum/military-aviation/17393-plaaf-offensive-combat-readiness-against-india-2.html, Citing Janes.com; http://www.ausairpower.net/APA-PLA-AAM.html#mozTocId749996