This brief reports a three-stage fully differential UWB amplifier with high and flat gain. It is proposed to be applied in the receiver part of a primary IR-UWB radar that is designed for real-time pedestrian localization. The amplifier was fabricated using 45 nm SOI CMOS technology and has been measured on a probe station and was demonstrated on a PCB. A differential cascode structure with positive feedback is employed and offers 45.8±0.5 dB gain (S 21 ) with a -3 dB bandwidth from 3.1 GHz to 10.6 GHz. The amplifier also achieves a wideband and flat input impedance matching with return loss smaller than -10 dB. The measured minimum noise figure is about 4 dB. The output power at 1 dB compression point is 10.2 dBm at 7 GHz. The amplifier occupies an active chip area of 0.4 mm 2 and consumes 125 mW from a 1.5 V supply. To the best knowledge of the authors, the proposed amplifier provides the highest gain and the best FOM in this frequency band in comparison with other designs that have been reported to date.