How to modelling an antenna in water in HFSS？

Hi all，
I??m designing an antenna which is working in the water.How can I modelling it in hfss if an antenna is imerged in water?Should I change the air box into water box?And will the size of it change?
Many thanks

Yes, wavelength changes heavily in water:
https://www.nature.com/articles/srep13535/figures/1

Also note the frequency dependent losses.

Thanks for your kindness.Also I found HFSS -> Boundaries -> Edit Global Material Properties,should I change this ?

Yes. This will affect the radiation boundaries' behavior such that they are matched to water, and not a vacuum.