A 15.5-dB conversion gain 0.35-μm SiGe HBT Gilbert mixer with the lumped-element Marchand balun for 3.1 GHz to 10.6 GHz UWB applications is implemented using standard silicon processes. This mixer has the 1.5-GHz IF 3-dB bandwidth as well as the 15.8-dB noise figure. The balun size is only (1.25 mm × 0.5 mm. Because of the balanced structure of the Marchand balun, the magnitude imbalance and phase difference of outputs are below 1 dB and about 184°, respectively. In the present of a lossy substrate, the dissipated loss of the balun is still less than 4 dB thanks to the advantage of the lumped-element technique. The total current consumption of the entire mixer is 13.9 mA at 5 V voltage supply while the chip size including probing pads is 1 mm × 0.9 mm.