I'm not sure but if you place the antenna on bottom side, you can place data signals on top side without degradation of RF signal.
If i've understand correctly, this is true only in theory.
The data signals could affect RF signals, and viceversa, depends on the "strenght" of that kind of signals.
In generally you can say, for low poer application, that GND and PWR plane shield enough the data/RF signals.
Just a curiosity, which device needs an RF antenna with GND plane underneath ?