A unique-planar vialess Marchand balun for V-band application is presented. The balun can achieve less than 2 • phase imbalance and 0.3 dB amplitude imbalance from 54 GHz to 66 GHz, with the insertion losses of −3.6 dB and −3.9 dB for the two balanced ports and the return loss of less than −15 dB in the unbalanced port. The novel back-to-back measured method has been proposed and analyzed, the amplitude and phase imbalances can be derived from the measured back-to-back two-port scattering results. The extracted results achieve good agreement with the single balun simulation, with no more than 0.15 dB and 1 • amplitude and phase differences. This balun configuration and the measurement method can simplify the fabrication, achieve good yield, ease the assembling and decrease the cost.