In this paper, we investigated the random phase rotation problem for multi-band orthogonal frequency-division multiplexing (MB-OFDM) ultrawide-band (UWB) systems. Random phase rotations need to be calibrated for coherent combining of MB channel information for high resolution time-of-arrival estimation. Our analysis indicates that in the presence of random phase rotations, resolution of MB-OFDM signals degrades which is reflected by increased energy leakage in the channel estimate. Based on this, we propose to calibrate random phase rotations across subbands by minimizing energy leakage. Simulation results show that the proposed technique performs well in 802.15.4a UWB channels.