In this paper a useful, simplex and broadband coaxial-to-microstrip transitions using GCPW, simple pre-transition, are designed and implemented. The GCPW, pre-transition section is utilized to provide a smooth transition from coaxial to microstrip. In this transition the effects of the field and impedance matching with considering possible fabrication errors in total performance are completely analyzed. Experimental results are very close with simulation results. The results of 50 mm length of Microstrip line with back-to-back transitions show that a ultra wideband transition with return loss better than −10 dB and in the worth case, total insertion loss is less than 1 dB up to 30 GHz. These good performances and its simplicity, easy fabrication and good performances make this proposed transition very useful in many applications such as UWB short range Radars up to 30 GHz and make it a very good candidate for higher frequencies.