Modern wireless communication equipment such as outphasing power amplifiers or systems like massive-MIMO rely heavily on transmission of complex wideband modulated radio frequency signals on parallel signal paths. As these signal bandwidths increase, wireless transmitters are more susceptible to amplitude and phase distortions across frequency. We propose a novel method to quantify the complex signal distortions in each transmit path and a technique to pre-compensate the transmitter over a wide bandwidth of interest. This work has been experimentally validated with measured results on two separate RF test benches using signal bandwidths up to 100 MHz. An outphasing power amplifier bench for WCDMA at S band requiring 4 signal paths and a satellite uplink modulator using 8- PSK at Ku band requiring two signal paths were tested in the experimental validation. Further, it is also validated that this method requires only one iteration to calibrate a set of parallel RF signal paths.