In this paper, the authors present a software defined radio six-port receiver for a novel broadband mobile communications system. The prototype covers the frequency range from 0.3 GHz to 6 GHz and operates with up to 100 MHz-wide channels. The multi-band and multi-mode demodulation capabilities of the six-port architecture have been experimentally demonstrated. The six-port receiver has been satisfactorily proved for high data rates (up to 93.75 Mb/s, limited by the available test instruments). An efficient six-port auto-calibration method suitable for large instantaneous bandwidth systems is presented and validated.