Neptune wrote:
The Flat Screen was a test. There's something special about it, but I can't really recall what at the moment. I THINK, it was a phased array like US SPY-1 type of radar (although this one is rotating of course). I'm not sure, but I think that was the special thing about it, it can take a lot more targets than the regular Top Plate or Fregat radars. Kerch and Azov were both used for testing later in their lives. Kerch is still there, she's receiving occasional upgrades as she's sponsored by the city of Kerch. For a long time, a lot of things were regulated and provided by the city which sponsored the ship (and I think that actually still stands as of now).
Flat screen antenna looks like a normal frequency scanned planar array with serpentine wave guide that loops back and forth across the face of the array similar to Top plate, or the likes of US SPS-48 and sps-39/52, just much bigger, so it either operate at much lower frequency, or have much higher resolution than similar but smaller radars.
Their predecessors Top sail/top pair were also frequency scanned set with much bigger antenna than their western counterparts and operated at much lower frequency than their western counterparts. So it wouldn’t be the first time if the Soviets used much lower frequency for their main 3D search radar than the west. There is a recently declassified early 1970 CIA assessment which suggest the Soviets may have chosen very low frequency for their main 3D search radar to enable them to take takes advantage of atmospheric phenomenon to gain some unusual capabilities such as seeing well below the horizon and extending their range by detecting turbulence or rising thermals in the air.