This article demonstrates a power-efficient frequency doubler with an integrated ADNFET-based two stage PA for a D-band FMCW imaging radar transmitter. The frequency doubler extracts the second harmonic through a push-push differential pair with superior amplitude and phase imbalance performance compared to conventional doubler designs. The two-stage PA applies ADNFETs for high output power and efficiency. The doubler-PA is fabricated in 45nm RFSOI with better than 12% peak drain efficiency and 10 dBm or greater output power performance from 114 - 126 GHz.