separate ground

Hi friends,
In my baseband system,it has three types ground:audio ground,digital ground and RF ground,my RF board is designed with another board that only have one type ground----all types of grounds are connected to the bottom ground layer(double side FR4 board),can be soldered on baseband board.My question is whether is necessary to sepatate ground into three types ground:audio ground,digital ground and RF ground?due to the ground is connected in RF part.Why?
Thanks,

in this forum you can find a detailed answer

https://www.edaboard.com/forum6.html

Any detail link to this topic?