A Gm-compensated 46-101 GHz broadband power amplifier for high-resolution FMCW radars is presented. For bandwidth expanding, a Gm compensator-based negative feedback chain is applied to the PA, compensating the large gain ripple caused by a high-k transformer-based ultra-wideband interstage matching network. Based on the proposed feedback Gm-compensated technique, the proposed PA achieves a 55-GHz bandwidth and 74.8% of the fractional bandwidth is obtained with <0.3 dB gain ripple in 53-92 GHz. The PA reaches 17.1 dBm Psat and 27% peak PAE respectively, and the core area is 0.1mm2 in TSMC 40nm CMOS process.