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A new low noise amplifier (LNA) with broadband input matching and excellent gain flatness operating at the frequency range of 3.1-4.8 GHz is designed using a 0.18 μm CMOS process. Wideband input matching using common-gate at the input stage is proposed. From a supply voltage of 1.8 V, the two-stage LNA exhibits a noise figure (NF) of 3.95-4.3 dB within the required bandwidth. The LNA has S11 less than -15 dB over the entire 3.1-4.8 GHz band. A reversed isolation (S12) less than -43 dB was achieved. A power gain (S21) of 16.5 dB with only 0.6 dB variations was obtained within the 3.1-4.8 GHz band. Input IP3 and 1 dB compression points are not of much concern in the case of the UWB LNA, since transmit power is restricted to be less than -42 dBm/Hz.