The YJ91 is a chinese made version of the Kh-31P (Type 77P) - passive radiation seeker head for use as an anti-radiation missile. Stays at high altitude throughout its flight, allowing higher speeds and increasing range to 110 km (60 nmi; 70 mi). The Kh-31P missile comes in three variants, each optimized against a different set of radiation sources, typically targeting enemy surface-to-air missile system

The Kh-31 (Russian: Х-31; AS-17 'Krypton') is a Soviet and Russian air-to-surface missile carried by aircraft such as the MiG-29, Su-35 and the Su-57. It is capable of Mach 3.5 and was the first supersonic anti-ship missile that could be launched by tactical aircraft.^[6]

There are several variants; the Kh-31 is best known as an anti-radiation missile (ARM) but there are also anti-ship and target drone versions. There has been talk of adapting it to make an “AWACS killer”, a long-range air-to-air missile