Abstract: A ground-penetrating radar (GPR) scanner for investigating a sub-surface, wherein the GPR scanner comprises an antenna assembly configured for transmitting and receiving ultra-wide band (UWB) signals. The GPR scanner further comprises a directional coupler, a UWB signal generator configured for providing outgoing UWB signals through the directional coupler to the antenna assembly, a UWB signal sampling unit configured for receiving incoming UWB signals from the antenna assembly through the directional coupler, and an impedance. The directional coupler is configured as a balanced UWB directional coupler. It comprises a first port configured for receiving positive outgoing UWB signals from the UWB signal generator and a second port configured for receiving negative outgoing UWB signals from the UWB signal generator, wherein the second port is balanced with the first port.