The long usage history of sonobuoys and underwater decoys in submarine warfare seems reason to suppose that the use of similar sacrificial systems within the realm of possible tactics to further avoid detection of a submarine.
(2) A parabolic antenna, or any other very directional antenna, requires a stable platform. Either it's on a huge inflatable raft, or the sub is rigidly attached. Either way, the operation will be noticed.
(3) Sacrificial systems in submarine warfare are rare. They exist but, like aircraft launching flares, they draw attention and are therefor only used once the sub has been somehow detected. Subs don't like anything that draws attention unless things are already hitting the fan.
I'm not sure if you are suggesting that an antenna would have to be detrimental to the radar cross-section of a submarine or if you are suggesting that you can intercept radio waves from a high directivity antenna.
For the former, directional antennas are on all forms of modern day stealth vehicles without compromising the radar cross-section of the vehicle (eg. modern jet fighters).
For the latter I have already seen successful systems such as MADL [1] which use highly directional radio waves to communicate between stealth fighter jets (something you would hope would go undetected). So I highly doubt that submarines couldn't have a similar system in place.
> (2) A parabolic antenna, or any other very directional antenna, requires a stable platform. Either it's on a huge inflatable raft, or the sub is rigidly attached. Either way, the operation will be noticed.
As shown in [1], directional radio waves can be sent from one jet fighter to another. Both of these are not stable platforms.
[1] https://en.wikipedia.org/wiki/Multifunction_Advanced_Data_Li...
Fighter aircraft as remarkable stable platforms. They spend 95%+ of their time wings-level, say +/- 5*. And most of the motions of an aircraft are commanded by the pilot, allowing electronics a momentary heads up to make decisions re antennas. Compare that to a tiny raft in even moderate seas, constantly moving in every dimension, where the random motion never, ever, stops. Many a fighter jock has suffered sea sickness.