This paper reports a 45-GHz low-noise amplifier (LNA) covering the 22.2% -1-dB fractional bandwidth (BW). The transformer-based magnetically coupling resonators are exploited and gain response staggering techniques are applied to improve the BW efficiency and gain flatness. A three-coil transformer-based gm-boosting common-gate scheme is utilised as the input matching network in order to improve the noise results. The prototype, which was fabricated via a 65-nm CMOS process, demonstrated a maximum gain of 30.5 dB and a minimum noise figure of 4.1 dB, while the -3-dB BW was 15 GHz and the -1-dB BW was 10 GHz, meaning that the band range for IEEE 802.11aj was fully covered. The LNA consumed 63.6-mW power with a 1.2-V supply and occupied an area of 0.47 × 1.00 mm.