A Ka-band low noise amplifier (LNA) is presented that improves the traditional source-degeneration LNA by utilizing broadband transformer matching and gate-drain feedback technology. The proposed LNA achieves an ultra-wideband LNA while maintaining the advantages of high integration and low power consumption of the traditional source-degeneration LNA. In addition, cascade technology is adopted to further improve peak gain. The proposed LNA is implemented in 55nm CMOS process. The simulated results show that the LNA achieves stable gain response in the 21.7-36.5 GHz frequency band, with a peak power gain of 20.8 dB. The minimum noise coefficient is 4.4 dB, and the DC power consumption is 15 mW. The LNA achieves a compact chip area of 0.33 mm ².