When a system work in radar mode, tracking radar track both, target and
missile and send correcting signals to missile through radio
transmitter. IR missile tracking system is part of optical sight and
work only in optical mode. If you have optical visibility to target, IR
missile tracking system will also have optical visibility to missile,
which is all the time between the launcher and target.
Quite true, though I think even in radar mode the optical tracking would still be useful as it would be more accurate than radar especially against very low flying targets.
The tracking of the missile in an engagement against aerial target would be effected if the target flys behind a cloud... the auto tracker will try to estimate the targets position based on its trajectory heading towards the cloud but that might not be accurate enough unless it is a small cloud.
In the fire control system for the Mig-29 the IRST and radar were linked so that a target acquired by the IRST could be handed over to the radar, or indeed used to align a missile seeker onto the target without the need for scanning.
In the case of say a TOR in optical mode this would greatly reduce the chance of electronic interference though it would not be electronically stealthy where a radar tracking beam (very narrow and not especially high power) could continue to track the target and a separate tracking beam for the missile to ensure a kill.
IR missile tracking system on optical sight is just part of optical mode
of working and that doesn't have any influence on their rule in air
What I am trying to get at is that the optical back up modes of these systems is not to protect them from HARMs, and other ARMs, it is more often to allow the system to operate under conditions of extreme jamming or malfunction.
The aircraft carrying HARM type weapons will be dealt with at longer ranges as will most of the missiles fired at these systems and the SAMs and radars they are protecting. At most these systems might have to deal with a few leaking missiles but that is well within their capability anyway.
But in helicopter like Ka-52, which have radar in its nose, radar could
track both target and missile and send correcting radio signals to
missile, what made ATGM all weather capable.
It is hard to say... the 35 GHz transmitter used for the ATAKA and SHTURM is a very high frequency, it really depends on the radar the Ka-52 uses. Remember the Mi-28N will use a MMW and CMW radar too yet it still sports the thimble nose transmitter for the ATAKA.
These missiles are very useful... cheap and accurate with the range to get the aircraft to the edge of MANPADs range and well out of small arms range, but they are only temporary and I think Hermes will be the primary ATGM used by Russian Helos. The ATAKA will likely remain in use for a while especially on the Mi-24s and Mi-28s as it is probably available in numbers with stocks of SHTURM likely available too. Once they are used up however the ATAKA might remain in low rate production for export and as a cheap alternative where HERMES is not needed or is too large like with light helos, and of course UCAVs.
Anyway... what I am trying to say is I think pictures showing Ka-52s with what appear to be ATAKA tubes is likely a temporary measure and that its primary weapon will likely be Hermes, Rockets for marking targets the old fashioned way and boxes of UAVs it can launch to explore at low risk.