FR4 is not very much recommended substrate for beyond 1-2GHz even it looks like working.A high quality and high dielectric substrates should be choosen for precise and application specific structures.Balun is one of them because here Gain and Phase balance is important for a proper performance.FR4 has also poor fabrication tolerances and di-electric coefficient shows some variations between manufacturers.
For 3GHz, lambda/4 will be 11.9mm for FR4 ( Er=4.4) substrate, 7.9mm for Alumina ( Er=9.8 ) and losses will be much less than FR4.