A broadband microstrip-to-coplanar waveguide (CPW) transition using two parallel folded balun structures with easy transmission band control for various RF circuits and integrated systems is proposed in this paper. Each balun is employed an open-circuited microstrip line and a short-circuited slotline with one quarter-wavelength long each. As the change of the length of the open and short circuits, the transmission band can be easily controlled. The measured return and insertion losses are better than 10dB and 1.4dB, respectively, over the bandwidth of 82.5% at the center frequency of 6GHz.