This picture has also one of the clearest shots of the 051B's ESM units which is on the right of the picture. This particular unit is not found in the 054A, but is with the 052C and 052D destroyers, and is identical to those units found in the 052C/D. The location though is different on the 052C/D, as this ESM unit is found next and behind to the Type 366 radar on top of the bridge, and ahead, and at the base of the mast.
While the SAM fit of the 051B refit is much like the 054A, the ECM/ESM fit of the 051B refit is more like the 052C/D.
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Its been a sub hobby of mine, but I have been looking for an OTH (Over the Horizon) ESM type DF (Directional Finder) on the ship. What this does, the Chinese equivalent to the US called Combat DF, or similar to AN/SRS-1A or COBLU; or to the Russian MINERAL ME or Bandstand antiship targeting system.
AN/SRS-1A
COBLU
Mineral ME
What these systems do, and what the passive component (Mineral ME-2) does is to target a ship via its emissions over the horizon for antiship missiles.
The Chinese have a copy of the MINERAL ME system called Type 366. There are modifications on the Type 366-1 to allow it for spotting sea skimmers, and Type 366-2 does OTH directional finding and targeting via passive detection. Type 366 system equips every Type 054A, 052C and 052D ship. Even the 051C has this. But its absent on the 051B and the refit did not add this. Yet the ship is equipped with all these long range YJ-12 missiles, and I am not certain it completely relies on helicopter and plane spotting for this. The ship also lacks the CEC unit that's been retrofitted to other destroyers including 051C, but maybe its not the 051B's turn yet to get one.
My theory is that these ESM units near the antiship missiles and below the Type 364 radar, serves that purpose. They are separate from the Type 726-1 and 726-2 ESM units located on the mast, and which is meant to support the Type 726-3 ECM and Type 726-4 decoy units. They are also located approximately in the same relative location the Type 366-2 appears on the 054A which below the Type 364 radar and the 052C/D, which is below the Type 517M radar. These units are also present on the 052C/D, located behind right and left of the Type 366 radar, which confuses me a bit, since this would suggest the 052C/D uses two separate sets of OTH directional finding.
Second and third batch of 052D shows a new ESM antenna, and the new antenna has been retrofitted in most 052C and on the Liaoning. Its installed on the 055 but radar deflectors above the bridge hides much of this unit except the top.