Don't know... perhaps.
There are too many unknowns with the antenna. The terminal velocity in water would be dependent on several factors:
1: initial velocity of the antenna on impacting the water.
2: Mass of the antenna.
3: Presenting cross section of the antenna related to orientation of fall.
4: The viscosity of the seawater.
5: Volume of the antenna (volume and mass may result in a specific density that is less than that of seawater giving the object bouyancy.)
6: Temperature of the various layers of seawater and any rising or falling currents.
It is possible for an object that is sufficiently heavy AND sufficiently thin (streamlined) to reach a very high velocity in almost any fluid (for this purpose air and water are both fluids)... but we need to know this and other information to calculate a terminal velocity.
Didn't know I was talking to somebody so edumacated.