FR4 would be a terrible material to use. It is not the er that matters, it is the loss tangent. Even at 1 GHz the loss tangent is above 0.01, which is very poor. See the wikipedia article on FR4, and read the references.
Greetings, obviously no. kindly check the data sheets of the material to be used before any design, where you could find the frequency range up to which the material could be used.