Folks are debating this latest Chinese AAM -- is a Chinese version of AIM120D or a PL-12 derivative optimized for internal-weapons-bay as featured by the J-20.
It was reported that 607 Institute has been developing a new activing radar homing AAM comparable to American AIM-120D (dubbed PL-15?). Recent photos showed a new type of missile being tested onboard a J-11B fighter. Compared to PL-12 of the same class, the missile features stablizing fins and tailfins with reduced wingspans, suggesting its design is optimized for internal carriage by the 4th generation fighter such as J-20. PL-1X may also features improved guidance system (including duplex datalink and new active/passive dual mode seeker with enhanced ECCM capability) as well as a bigger motor which gives it a longer range (~100km?). There was a speculation that PL-1X is actually a new anti-radiation AGM comparable to American HARM, but this has yet to be confirmed.
