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An ultra-wideband (UWB) low-noise amplifier (LNA) is proposed with a wideband input matching circuit consisting of a simple second-order Chebyshev filter which reduces the order of the filter, considering loaded parasitic elements. An equivalent circuit including an input matching network and loaded parasitics is analysed for an optimised input reflection coefficient in the UWB full band through calculation and parametric analysis. All loaded parasitics are carefully examined and a crucial parameter with a significant effect on the input matching is determined. The measured input matching corresponds well with the simulated result from the equivalent circuit. The proposed LNA achieves a -3-dB gain bandwidth from 2.5 to 10.5-GHz, a minimum noise figure of 2.8-dB, a maximum power gain of 15.3-dB and an input matching lower than -10-dB. The measured input-referred 1-dB compression is -17-dBm at 7.1-GHz and the measured group delay is about 150-60-ps while consuming 11.6-mW from 1.8-V and 6.4-mA. The LNA is fabricated in a 0.18--m complimentary metal-oxide semiconductor (CMOS) process and the total chip size including testing pads is 1.04-mm2.