A 3.1-10.6 GHz ultra wideband (UWB) low noise amplifiers (LNA) was designed in 0.35-mum SiGe BiCMOS technology. The circuit technique of multiple feedback loops was adopted to achieve the matched input terminal impedance and wide bandwidth simultaneously. In the focused band this LNA has a peak gain of 19dB with a ripple of less than 2dB, an input return loss of less than -12dB and a noise figure (NF) of less than 3.5dB. The power consumption is 30mW under a 3.0V supply. Compared with the recently reported CMOS UWB LNA, the simulation results show that this LNA has broader bandwidth, lower NF and simpler input matching network